JP2017516190A - Reduction of controller update in control loop, method for controlling controlled device, process control system, process controller - Google Patents

Abstract

The control technique reduces the number of changes by the controller provided to the controlled device, thereby reducing the power consumption of the controlled device along with the load of the process control communication network located between the controller and the controlled device. Control the process in a reduced manner. This technique is very useful in many cases in control systems with wirelessly connected field devices such as sensors and valves that operate on battery power. Furthermore, the control technique is useful in implementing control systems where control signals are prone to communications that are intermittent, asynchronous, or significantly delayed and / or used as feedback signals in closed-loop control. Useful in control systems that receive intermittent, asynchronous, or significantly delayed process variable measurements. [Selection] Figure 4

Description

  This patent relates to performing control in a control loop that has low speed, intermittent or aperiodic communication, and more specifically, in a manner that reduces the number of controller updates provided to the controlled device. And control routines using aperiodic signaling.

Cross-reference of related applications

  This application is a normalized application claiming priority over US Provisional Patent Application No. 61 / 968,159, filed March 20, 2014, entitled “Reduce Controller Updates in a Control Loop”. The entire disclosure of which is expressly incorporated herein by reference. This application is also a continuation-in-part of U.S. Patent Application No. 13 / 351,802, filed January 17, 2012, entitled "Compensating for Setpoint Changes in a Non-Periodic Updated Controller". The entirety is expressly incorporated herein by reference. This application is also related to US patent application Ser. No. 11 / 850,810, filed on Sep. 6, 2007, entitled “Wireless Communication of Process Measurements,” which was filed on Aug. 4, 2006. US patent application Ser. No. 11 / 499,013, a continuation-in-part of the name “Process Control With Unreliable Communications”, issued as US Pat. No. 7,620,460, which was published in 2005. No. 11 / 258,676, filed Oct. 25, entitled “Non-periodic Control Communications in Wireless and Other Process Control” In continuation-in Systems ", which was issued as U.S. Patent No. 7,587,252, the entire disclosures of each of which is incorporated expressly herein by reference.

  Process control systems such as distributed or expandable process control systems, such as those used in chemical, petroleum, or other processes, typically via an analog bus, a digital bus, or a combined analog and digital bus. One or more process controllers communicatively coupled to each other, to at least one host or operator workstation, and to one or more field devices. For example, field devices, which can be valves, valve positioners, switches, and transmitters (eg, temperature, pressure, and flow sensors) function in processes such as opening or closing valves and measuring process parameters. I do. The process controller receives signals indicating process measurements created by the field device and / or other information about the field device and uses this information to implement a control routine to generate a control signal and Signals are sent to the field device over a line or bus to control the operation of the process. Information from field devices and controllers is typically available to one or more applications executed by an operator workstation. Allows the operator to perform any desired function on the process, such as checking the current state of the process, modifying the operation of the process, etc.

  Some process control systems, such as the DeltaV ™ system sold by Emerson Process Management, control using a functional block or group of functional blocks, called modules, located on a controller or different field devices. Performing operations and / or monitoring operations. In these instances, the controller or other device may include and execute one or more functional blocks or modules, each of which is another functional block (either in the same device or in a different device). Input and / or provide output to other functional blocks, such as process parameter measurement or detection, device monitoring, device control, or implementation of a proportional-integral-derivative (PID) control routine, etc. Perform some process operation, such as performing a control operation. Different functional blocks and modules within a process control system are generally configured to communicate with each other (eg, via a bus) to form one or more process control loops.

  A process controller is typically defined in terms of a process or included in a process such as a flow control loop, temperature control loop, pressure control loop, etc., for each of a number of different loops, different algorithms, subroutines. Or programmed to execute a control loop (these are all control routines). Generally speaking, each such control loop has one or more input blocks, such as analog input (AI) function blocks, one or more controls, such as proportional-integral-derivative (PID) or fuzzy logic control blocks. And output blocks such as analog output (AO) functional blocks. Control routines and functional blocks that implement such routines are configured according to a number of control techniques, including PID control, fuzzy logic control, and model-based techniques such as Smith Predictor or Model Predictive Control (MPC). Yes.

  To support the execution of control routines, a typical industrial plant or process plant has a centralized control room that is communicatively connected to one or more process controllers and process I / O subsystems, The process I / O subsystem is connected to one or more field devices. Traditionally, analog field devices are connected to the controller by a two-wire or four-wire current loop for both signal transmission and power supply. An analog field device such as a sensor or transmitter that transmits a signal to the controller modulates the current flowing through the current loop so that the current is proportional to the sensing process variable. On the other hand, an analog field device that performs an action under the control of the controller is controlled by the magnitude of the current passing through the loop. Numerous digital field devices or analog and digital field devices receive or transmit control signals or measurement signals via digital communication networks or analog and digital communication networks.

  As data transfer increases, one particularly important aspect of process control system design is that field devices are communicatively coupled to a controller in the process control system or process plant, and to other systems or devices. Including the style. In general, the various communication channels, links, and paths that enable a field device to function within a process control system are generally referred to collectively as an input / output (I / O) communication network.

  The communication network topology and physical connections or paths used to implement an I / O communication network can make field device communication robust or sound, especially when the network is subjected to harmful environmental factors or harsh conditions. Can have a significant impact. These factors and conditions can compromise the soundness of communication between one or more field devices, controllers, and the like. Communication between the controller and the field device is particularly sensitive to any such disruption because the monitoring application or control routine typically requires periodic updates of process variables for each iteration of the routine. . Thus, impaired control communication can result in reduced efficiency and / or profitability of the process control system, excessive wear or damage to the equipment, and any number of potentially harmful failures.

    In order to ensure robust communication, I / O communication networks used in process control systems have historically been hardwired. Unfortunately, hardwired networks introduce numerous complexity, challenges, and limitations. For example, the quality of a hardwired network can degrade over time. In addition, a hard-wired I / O communication network, particularly when the I / O communication network is associated with a large industrial plant or facility that is distributed over a large area, such as a refinery or chemical plant that consumes several acres of land. Are typically expensive to install. The long wiring installation required is typically labor intensive, material and expensive, and may introduce signal degradation resulting from wiring impedance and electromagnetic interference. For these and other reasons, hardwired I / O communication networks are generally difficult to reconfigure, modify, or update.

  A more recent trend has been to use wireless I / O communication networks to mitigate some of the problems associated with hardwired I / O communication networks. For example, U.S. Patent Application Publication No. 2003/0043052, the name “Appratis for Providing Redundant Wireless Access to Field Devices in a Distributed Control Wire”, the entire disclosure of which is expressly incorporated herein by reference. Disclosed is a system that utilizes wireless communications to increase or supplement the use of wireless communication.

  However, reliance on wireless communications for control-related transmissions is traditionally limited due to reliability concerns, among other things. As explained above, modern monitoring and process control applications rely on reliable data communication between the controller and field devices to achieve optimal control performance. In addition, a typical controller executes a control algorithm at high speed to quickly correct undesirable deviations in the process. Undesirable environmental factors or other adverse conditions can cause intermittent interference that interferes with or prevents the high speed or periodic communications necessary to support such execution of the monitoring and control algorithms. Fortunately, wireless networks have become much more robust over the past decade and have allowed reliable use of wireless communications in several types of process control systems.

  However, power consumption is still a complicating factor when using wireless communications in process control applications. Since wireless field devices are physically separated from the I / O network, the field devices typically need to provide their own power source. Thus, the field device can be battery powered, extract solar energy, or extract environmental energy such as vibration, heat, pressure. For these devices, the energy consumed for data transmission may occupy a significant portion of the total energy consumption. In fact, it is more during the process of establishing and maintaining a wireless communication connection than during other important operations performed by the field device, such as steps taken to detect or detect the process variable being measured. It may consume a lot of power. In order to reduce the power consumption of the wireless process control system and thus extend battery life, it has been proposed to implement a wireless process control system in which field devices such as sensors communicate with the controller in an aperiodic manner. In one case, the field device may communicate with the controller or send a process variable measurement to the controller only when a significant change in the process variable is detected, leading to aperiodic communication with the controller. it can.

  One control technique developed to handle non-periodic process variable measurement updates provides an indication of the expected process response to control signals generated by the controller during rare aperiodic measurement updates. Use a control system to provide and maintain. The predicted process response can be developed by a mathematical model that calculates the predicted process response for a control signal for a given measurement update. An example of this technique is described in US Pat. No. 7,587,252, entitled “Non-Periodic Control Communications in Other Process Control Systems,” the entire disclosure of which is expressly incorporated herein by reference. ing. Specifically, this patent generates an indication of the expected process response to a control signal upon receipt of an aperiodic process variable measurement update, until the arrival of the next aperiodic process variable measurement update Discloses a control system having a filter that maintains a generated indication of an expected process response. As another example, US Pat. No. 7,620,460, the title “Process Control With Unreliable Communications”, the entire disclosure of which is expressly incorporated herein by reference, is an expected response to control signals. Including a filter that further modifies the filter to incorporate a measurement of time elapsed since the last aperiodic measurement update to produce a more accurate indication of the expected process response The system is disclosed.

  Over the last five years, however, field instrument manufacturers have introduced a wide variety of WirelessHART® transmitters. Initially, these transmitters were only used to monitor the process. However, with the introduction of the techniques described above, it is possible to use radio measurements for closed loop control applications. Based on the wide acceptance of wireless transmitters, many manufacturers are developing and introducing wireless on / off valves and throttle valves.

  However, there are several technical challenges that must be addressed so that such wireless valves can be used in closed loop control. Specifically, a wireless valve typically only uses a limited amount of power, and, for example, to drive the valve to its target position in response to receiving a control signal, It is expected that most of the available power will be needed to change the target position of the valve. However, typical control techniques attempt to send multiple control signals to the device being controlled in order to ensure robust control performance. However, the high number of controller-based movements performed by these techniques can quickly drain battery resources in the controlled device. Therefore, if possible, it may be desirable to reduce the number of valve movements performed during the closed loop control, for example, in response to changes in set points, process disturbances, and the like.

  Further, in many instances, control system actions are synchronized with gateway communications that must occur to provide communication between the controller and other actuators located within the wireless valve or wireless communication network. I can't let you. For example, current designs of wireless gateways, such as WirelessHART® gateways, cannot function immediately upon request to communicate valve position changes to the valve actuator, so the valve or actuator is controlled by the controller. After generating the signal, it may take some time to receive the control signal. Furthermore, the controller may only receive an acknowledgment from the valve or actuator for a longer time after a change in valve position is transmitted by the controller. Thus, in this case, wireless communication of the target valve position (eg, control signal) and valve response introduces a significant variable delay into the control loop, and this delay affecting PID control is controlled by the controlled variable. Makes robust control more difficult.

  For example, control techniques that can be used in a PID control loop significantly reduce the number of communications from a controller (eg, a PID controller) in a process plant to a radio valve or other control element while still being controlled. Provides robust control of process variables. In this way, less power has to be reacted at the target valve position, so less power is used by the radio valve or other control elements, while still being acceptable and robust. Provide control. In addition, the present technique allows for less communication to the radio valves or other controlled elements, so this control in a plant where the controller is communicatively connected to the controlled device via a gateway to the radio network. Using the technique reduces the communication load of the gateway. The control technique can be used in conjunction with other intermittent or aperiodic control methods, thereby using one or both of a radio transmitter and a radio valve (or other radio control element) in the control loop. And can be controlled. In addition, the technique may be unnecessary or otherwise, such as valve position hunting, typically experienced in noisy control systems where the feedback measurements are noisy or where the noise results in a relatively random process disturbance. It can be used to control in wired or other periodic control systems to reduce invalid valve movement.

  In addition, new control signal commands are used to control over wireless or other intermittent, aperiodic, or asynchronous communication networks to support the control performance of the control techniques described herein. A signal can be transmitted. The new controller signal can include a target value and a time to implement the target value. This command signal or other signal allows the controller to more accurately calculate the implied valve position, and therefore can be used to (for example, between a process controller and a controlled device such as a valve) Better or more robust control can be achieved with systems that experience significant communication delays in process control loop communications.

  Generally speaking, a control loop that implements a new aperiodic communication technique is a wireless, between a controller that implements a control routine (such as a PID control routine) and a controlled device such as a valve or valve actuator. It may include slow, aperiodic, or asynchronous communication connections or paths. This link can be implemented using a wireless or wired communication infrastructure. In this case, the control technique uses an aperiodic communication block that is placed between the controller and the controlled device, which reduces the number of control signals sent to the controlled device. To act to minimize the number of changes made to the target position of the controlled device.

  More specifically, in order to minimize the power consumed by the valve actuator, the controller's calculated PID output is transmitted to the wireless valve only when certain criteria determined by the aperiodic communication block are met. can do. Since the controller is typically scheduled to run to generate a control signal much faster than the minimum period at which the target value can be communicated to the wireless controlled device, the application of these criteria is Reduce the number of controller signals sent to the controlled device, thereby reducing controller movement performed by the controlled device. However, the application of the criteria within the communication block still ensures that sufficient control performance is achieved with a reduced number of control signals and in the presence of communication delays of the control signals for the controlled device. To work. As an example, an aperiodic communication block operates to communicate a new target position (via a wireless, intermittent, asynchronous, or aperiodic communication path) to a controlled device in the following manner: Can do. Initially, the aperiodic communication block is controlled for the last change in the target position transmitted from the last communication to the wireless controlled device that is greater than or equal to the configured communication period and sent to the controlled device. A control signal is transmitted only when a device acknowledgment communication is received. When these conditions were met, the aperiodic communication block exceeded the configured deadband value (threshold) as the absolute value of the difference between the calculated controller output and the last target value communicated to the controlled device Communicate new or updated control signals when and / or when the time since the last communication to the controlled device exceeds the configured default reporting time.

  The target position communicated to the wireless controlled device is usually an output calculated by a controller such as a PID controller. However, as an option, the magnitude of the change in the target position is the last when the absolute value of the change in the controller output since communicating the last target is determined to exceed the configured maximum change value. It can be limited to add or subtract the communicated value and the maximum change value.

  When minimal delay is introduced by communication between the wireless controlled device and the controller, a feedback signal in the form of a valve position is communicated to the controller by the wireless controlled device (eg, actuator / valve). For example, it can be used in the controller positive feedback network to create a reset contribution of the PID control signal. However, if communication with the wireless controlled device is lost or is not updated in a periodic manner, the last target position of the controlled device communicated by the wireless valve (e.g., the valve actuator operates to achieve). Can be used to determine the reset contribution of the controller operation. In order to assist the control system feedback loop in determining the valve position for use in calculating the reset contribution, the control system (or wireless gateway) allows the control valve (eg, the position that the valve must move to). ) And the time that the valve must make such a movement. Such control signals are useful in situations where the control signal takes a significant amount of time to reach the controlled device (eg, caused by a wireless gateway or a low speed or asynchronous communication link). As the time specified in the control signal, for example, an absolute time or an offset time from the time stamp of the control signal can be specified. If the offset time is configured to be longer than the time it takes for the control signal to reach the controlled device from the controller, the controlled device receives the control signal and implements the change at the specified time. In this case, the controller can be considered to have received and implemented a control signal by the controlled device at a specified time, thereby providing a feedback signal from the controlled device indicating that the controller movement has been performed. At that time, the valve position can be updated in the controller's feedback loop. This operation can result in better control performance of the PID controller.

1 is a block diagram of a typical, periodically updated, hardwired process control system. FIG. 6 is a graph illustrating a process output response to a process input of one embodiment of a periodically updated hardwired process control system. A controller that transmits a control signal to a controlled device in an aperiodic or wireless manner via a wireless gateway device and / or receives a feedback signal that is aperiodically, asynchronously or significantly delayed via a wireless network FIG. 1 is a block diagram illustrating an example of a process control system having Control is performed using a communication module of a periodic control signal disposed between the controller and the controlled device, communication between the controller and the controlled device occurs through a wireless communication network, and the communication module is FIG. 3 is a block diagram of one embodiment of a controller that operates to reduce the number of controller signals transmitted to a controlled device. Implement a non-periodic control communication technique to reduce the number of control signals transmitted to a controlled device via a wireless communication network or intermittent, low speed, or asynchronous communication network, and further, wireless, low speed, or 1 is a block diagram of a process control system that receives a feedback signal via an intermittent communication path. FIG. 1 is a block diagram of a process control system that implements an aperiodic control communication technique that reduces the number of control signals transmitted to controlled devices in a communication network that uses wired or synchronous communication. FIG. FIG. 7 is a block diagram illustrating a process of using a write request and a write response to achieve the periodic control communication of FIGS. 4-6. Used to achieve control signal communication from the controller to the controlled device using the control communication techniques described herein, including control signals that specify the time to apply control movement. FIG. 6 is a diagram illustrating a timing diagram of a set of signals. Various parameters associated with two process control simulations performed using the control communication techniques described herein, and the same parameters in similar control systems using typical wired or periodic control communication It is a figure which illustrates a graph. Various parameters associated with two process control simulations performed using the control communication techniques described herein, and the same parameters in similar control systems using typical wired or periodic control communication It is a figure which illustrates a graph.

  Control techniques reduce the number of actuator movements achieved by the actuator, while the controller is aperiodic, wireless, slow, significantly delayed to provide robust control performance, otherwise Allows control signals to be communicated or transmitted to the controlled device of the process, such as a valve actuator, in an asynchronous manner. Thus, the present control technique implements a control method that drives an actuator or other controlled device in a manner that reduces the power consumption of the controlled device, and frequently occurs in control loops that experience significant noise or process disturbances. Reduce the frequent changes of controlled devices that result in the “hunting” phenomenon that occurs, and reduce the communication load on communication devices in the wireless network used to implement the control loop, such as in wireless gateway devices.

  Specifically, the control communication block in the control loop is a newly created control generated by the controller in an aperiodic fashion based on a number of components such as communication deadband, control signal change threshold, and communication period. Operates to send signals. Furthermore, in order to adapt to the control of the device in the presence of a delay control signal, the continuously updated filter in the controller repeats each control routine of the controller based on the actual or implicit position of the controlled device. In the meantime, an indication of the expected process response (also called feedback contribution) is generated. This feedback contribution is made in the controller to ensure proper control in the presence of significant delays between the controller that generates the control signal and the controlled device that receives the control signal and acts accordingly. used. In some cases, the continuously updated filter is expected, in part, from the last control routine iteration to generate an indication of the expected response during each control routine iteration. Instructions generated prior to response and control routine execution cycles can be used.

  In addition, when the process measurement feedback signal is provided to the controller in an intermittent, aperiodic, or delayed manner, the current output of the filter that is continuously updated receives a new measurement indication Only sometimes it can be used as a feedback contribution, such as an integral (also known as reset) and / or derivative (also known as rate) contribution in the controller. Generally speaking, in this case, the integration output switch is an anticipation generated by a continuously updated filter when the controller receives the last measurement update as an integral or reset contribution to the control signal. Maintained process response. When a new measurement update is available, the integral output switch will change to a new indication of the expected process response generated by the continuously updated filter (based on the new measurement update indication). Clamp and provide the new expected process response as an integral or rate contribution of the control signal. As a result, during each controller iteration, the controller uses a continuously updated filter to determine the new expected response of the process, and each new expected process response controller updates the new feedback value. Reflects the effect of changes made in the time between measurement updates, even if the integral or reset component of the control signal generated by the controller changes only when it is available at Affects the controller output during the development of the control signal.

  A process control system 10 illustrated in FIG. 1 that can be used to implement the control methods described herein includes a data historian 12 and each a display screen via a communication line or bus 9. A process controller 11 is connected to one or more host workstations or computers 13 having 14 (which can be any type of personal computer, workstation, etc.). The communication network 9 can be, for example, an Ethernet network, a WiFi network, or any wired or wireless network. The controller 11 is also connected to field devices 15-22 via input / output (I / O) cards 26 and 28 and also uses one or more hardwired communication networks and communication schemes. 15 to 22 are illustrated as being communicably connected. Data historian 12 is any desired type of data collection unit with any desired type of memory for storing data and any desired or known software, hardware, or firmware. Can do.

  In general, field devices 15-22 can be any type of device such as sensors, valves, transmitters, positioners, etc., while I / O cards 26 and 28 may be any desired communication. Or any type of I / O device that conforms to the controller protocol. The controller 11 includes a processor 23 that performs or supervises one or more process control routines (or any module, block, or subroutine thereof) stored in the memory 24. Generally speaking, the controller 11 communicates with the devices 15-22, the host computer 13, and the data historian 12 to control the process in any desired manner. In addition, the controller 11 implements a control strategy or scheme using what is commonly referred to as a function block, each function block (link and link) for implementing a process control loop within the process control system 10. An object or other part (eg, a subroutine) of the overall control routine that operates with other functional blocks (via called communication). The functional block is typically an input function, PID, fuzzy logic control, such as associated with a transmitter, sensor, or other process parameter measurement device to perform some physical function within the process control system 10. One of the control functions, such as associated with a control routine that performs, or the like, or an output function that controls the operation of some devices such as actuators or valves. Of course, hybrid and other types of functional blocks exist and can be utilized herein. The functional blocks can be stored and executed by the controller 11 or other device, as described below.

  As illustrated in decomposition block 30 of FIG. 1, controller 11 may include several single loop control routines, illustrated as control routines 32 and 34, and if desired, control loops. One or more advanced control loops, exemplified as 36, can be implemented. Each control loop is typically referred to as a control module. Single loop control routines 32 and 34 are suitable analogs that can be associated with process control devices such as valves, measurement devices such as temperature and pressure transmitters or sensors, or any other device within the process control system 10. Perform single loop control using single input / single output fuzzy logic control block and single input / single output PID control block connected to input (AI) and analog output (AO) functional blocks respectively It is illustrated as follows. The advanced control loop 36 is illustrated to include an advanced control block 38 having an input communicatively connected to one or more AI function blocks and an output communicatively connected to one or more AO function blocks. However, the inputs and outputs of the advanced control block 38 may be connected to any other desired functional block or control element to receive other types of inputs and provide other types of control outputs. Can do. The advanced control block 38 can implement any type of multi-input, multi-output control scheme, and is also a model predictive control (MPC) block, neural network modeling or control block, multi-variable fuzzy logic control block, real-time optimizer. Blocks or the like can be configured or included. The functional blocks illustrated in FIG. 1, including the advanced control block 38, can be executed by the stand-alone controller 11, or alternatively, one of the workstations 13 or of the field devices 19-22. It will be understood that it can be located and executed in any other processing device or control element of the process control system, such as one. As an example, field devices 21 and 22 can be transmitters and valves, respectively, and can execute control elements to implement control routines, such as one or more functional blocks, etc. , Processing components for implementing a portion of the control routine, and other components. More specifically, the field device 21 can have a memory 39A for storing logic and data associated with the analog input block, while the field device 22 is configured as illustrated in FIG. An actuator having a memory 39B for storing logic and data associated with a PID or other control block in communication with an analog output (AO) block may be included.

The graph of FIG. 2 is generally of control loops 32, 34, and 36 (and / or any control loop that incorporates functional blocks present in field devices 21 and 22 or other devices). FIG. 6 illustrates a process output that is deployed in response to a process input of a process control system based on one or more implementations. The implemented control routine is generally executed in a cyclic manner through a number of controller iterations, depending on the number of executions of the control routine shown along the time axis by the thick arrow 40 in FIG. In the conventional case, each control routine iteration 40 is supported by updated process measurements, indicated by thin arrows 42, provided by a transmitter or other field device, for example. As illustrated in FIG. 2, there are typically a plurality of periodic process measurements 42 made and received by the control routine during each of the periodic control routine execution times 40. In order to avoid the limitations associated with synchronizing measurements and control execution, many known process control systems (or control loops) attempt to oversample process variable measurements by a factor of 2 to 10 times. Designed to. Such oversampling helps to ensure that process variable measurements are up-to-date for use in the control scheme during the execution or iteration of each control routine. Also, to minimize control variation, conventional designs stipulate that feedback-based control should be performed 4-10 times faster than the process response time. Still further, in conventional designs, control signals deployed at the output of the controller during each controller execution period affect or achieve the operation of the controlled device to ensure the best control performance. To be sent to the controlled device. The process response time depends on the process time constant (τ) (eg 63% of the process variable change), the process delay or dead time (T _D ) after the step change 44 of the process input (on the lower side of FIG. It is represented in the process output response curve 43 of the graph of FIG. 2 to be the time associated with the addition of (shown by line 45). In any case, to meet these conventional design requirements, the process measurement update (indicated by arrow 42 in FIG. 2) is much more than the control routine execution rate (indicated by arrow 40 in FIG. 2). Fast and therefore sampled at a rate that is much faster than the process response time or higher and is provided to the controller.

  However, in some control system configurations where the controller transmits a control signal or receives process variable measurements wirelessly from one or more field devices, in a synchronous manner or with control signal transmission and reception. Sending control signals to the controlled device in a manner that ensures that each output of the controller reaches the controlled device with only minimal time delay between receipt of the signal at the controlling device May not be possible. Further, in these types of systems, it may not be practical or possible to obtain measurement samples from the process at high frequency and frequency. Specifically, in these cases, the controller may only be able to receive aperiodic process variable measurements and / or between aperiodic and even periodic process variable measurements. The time may be longer than the control routine execution rate (indicated by arrow 40 in FIG. 2).

  FIG. 3 may present the problems discussed above, and therefore may not be able to perform acceptable or desired control using the exemplary control techniques described with respect to FIG. 1 illustrates an exemplary partial wireless process control system 10. However, the new control techniques described herein with respect to FIGS. 4-10 provide control in a manner that minimizes control movement of the controlled device, while process control between the controller and the controlled device. The plant configuration of FIG. 3 for controlling in the presence of signals and / or aperiodic, wireless, and / or significantly delayed communications of process variable measurements between sensors or transmitters and controllers Can be implemented. Specifically, the control system 10 of FIG. 3 is essentially similar to the control system 10 of FIG. 1, and the same elements are labeled with the same numbers. However, the control system 10 of FIG. 3 includes a number of field devices that are communicatively coupled to each other in a wireless network 72 such as a WirelessHART® communication network and that are coupled to the controller 11 via a gateway device 73. 60-70 included. As illustrated in FIG. 3, wirelessly connected field devices in network 72 cooperate with each other and antenna 76 (coupled to gateway device 73) to communicate wirelessly within network 72. Or including the antenna. In one instance, some of the field devices illustrated as devices 61-64 are connected to a wireless gateway or conversion device 76 via hardwired lines and communicate within the wireless network 72 for the field devices. . Of course, other devices in the wireless network 72 can be wireless devices, and each can have its own wireless communication module for wireless communication within the network 72. Further, the field devices 60-70 can be any type of field device including, for example, a transmitter, an actuator (such as a valve actuator), a valve, and the like.

  As will be appreciated, each of the transmitters 60-64 and 66-69 of FIG. 3 may be used for wireless communication network 72, gateway devices for use in one or more control loops or control routines implemented in controller 11. 73 and the network 9 can be used to transmit signals indicating the respective process variables (eg, flow, pressure, temperature, or level signals) to the controller 11. Other wireless devices referred to as controlled devices, such as the valves or valve actuators 65 and 70 illustrated in FIG. 3, may be wireless (eg, via network 9, gateway 73, and wireless network 72) or The process control signal can be received from the controller 11 partially wirelessly. In addition, these devices send other signals (eg, signals indicating any other process parameters, such as the current position or status of the device, an acknowledgment signal) through the wireless network 72 in the plant 10. It can be configured to transmit to the controller 11 and / or other devices. Generally speaking, as illustrated in FIG. 3, the controller 11 detects a communication stack 80 that executes in the processor 23 to process the incoming signal, and when the incoming signal included a measurement update. A module or routine 82 that executes on the processor 23 to detect or detect other signals within or associated with the control loop, and a processor to control based on the measurement update One or more control modules 84 executing at. The detection routine 82 can generate a flag or other signal to indicate that the data provided via the communication stack 80 includes new process variable measurements or other types of updates. New data and update flags can then be provided to one or more of the control modules 84 (which can be functional blocks), which are then described in more detail below. And executed by the controller 11 at a predetermined periodic execution rate. Alternatively or in addition, new data and update flags may be provided to one or more monitoring modules or applications that are executed at the controller 11 or elsewhere in the control system 10.

  Thus, as described above, the process control system 10 of FIG. 3 generally performs other controls, such as transmitters 60-64 and 66-69, or field devices 65 and 70, to provide control. Uses wireless communication of control signals and data measured, detected or calculated by the element. As an example, in the control system 10 of FIG. 3, a new control signal from the controller 11 to a controlled device such as one of the valves 65 or 70 is transmitted to that device via the gateway device 73 and the wireless network 72. Is done. Further, in some cases, new process variable measurements or other signal values used to calculate the feedback of controller 11 are aperiodic, intermittent, or slow only when certain conditions are met. Can be transmitted to the controller 11 via the wireless network 72 by the devices 60 to 64 and 66 to 69 based on. For example, a new process variable measurement can be sent to the controller 11 when the process variable value changes by a predetermined amount with respect to the last process variable measurement sent by the device to the controller 11. Of course, other ways of determining when to transmit process variable measurements in an aperiodic manner can be implemented as well or alternatively.

  In any case, between the controller 11 (which performs control calculation) and the controlled device (eg, a valve or actuator device) that receives the control signal, and the sensor (which measures a variable of the controlled process) and the controller 11 The presence of the wireless communication network 72 in the communication path and / or the use of the gateway device 73 (using the sensor signal in the control calculation feedback loop) makes the communication in the control loop asynchronous, non-periodic. And / or experience significant delays during communication. For example, a typical wireless gateway to a WirelessHART® network may delay control communications for 3-6 seconds, making high speed synchronization control difficult when using these networks. Such a delay may also occur when signals are transmitted from a sensor or transmitter device in a wireless communication network to a controller outside the network.

  Accordingly, the presence of wireless communication between the controller 11 and devices in the wireless network 72 of FIG. 3 generally results in asynchronous, significantly delayed, and / or aperiodic communication, and thus the controller 11. And field devices 60-64 and 66-69, and / or vice versa, also results in irregular or otherwise infrequent data transmission. However, as mentioned above, the communication of control signals to and from the wired field devices 15-22 has traditionally been done in a periodic manner and then the control routine (s) within the controller 11 Yes) has been built to support periodic execution. As a result, the typical control routine of the controller 11 is generally designed to periodically update the process variable measurements used in the controller 11 feedback loop.

  In order to adapt to control and measurement signals, for example aperiodically or otherwise significantly delayed in the control loop, introduced by radio communication hardware arranged between the controller 11 and at least some of the field devices , The control and monitoring routine (s) of the controller 11, as described below, and particularly when using non-periodic or other intermittent or significantly delayed communication signals, When transmission occurs less frequently than the execution rate (eg, periodic execution rate) of the controller 11, it can be reconfigured or modified to allow the process control system 10 to function properly.

  An exemplary control scheme or control system 400 configured to operate using aperiodic control-related communications is illustrated in more detail in FIG. A controller 100 is schematically shown. More specifically, the controller 100 is coupled to the wireless actuator 102 of the process 101 via a wireless communication link 103 (illustrated with a dashed line in FIG. 4). In this case, the actuator 102 is a controlled device and can be an actuator for a valve that controls fluid flow within the process 101, for example. The control scheme implemented by the controller 100 (which may be the controller 11 of FIGS. 1 and 3 or a control element of a field device, such as one of the wireless field devices of FIG. 3, etc.) generally , Including the functionality of one or more of the communication stack 80, update detection module 82, and control module 84 illustrated and described in connection with FIG.

  In the exemplary system of FIG. 4, the controller 100 may be connected to, for example, one of the workstations 13 (FIGS. 1 and 3) or any other source within or in communication with the process control system 10. From the output of the controller 100 via the wireless communication link 103 and operates to generate one or more control signals 105 (or movement of the controller) that are provided to the wireless actuator 102. In addition to receiving the control signal 105, the process 101 (or the actuator 102, which can be within the process 101) may be subjected to measured or unmeasured disturbances. Depending on the type of process control application, the set point signal can be changed at any time during control of the process 101, such as an adjustment routine, by a user or the like. Of course, the process control signal can control an actuator associated with a valve or any other type of movable control element, or control any other field device to cause a change in the operation of the process 101. be able to. The response of process 101 to a change in process control signal 105 is measured or sensed by a transmitter, sensor, or other field device 106, such as one of transmitters 60-64 or 66-69 illustrated in FIG. It can correspond to any one. The communication link between the transmitter 106 and the controller 100 is illustrated in FIG. 4 as being a hardwired communication link that provides the controller 100 with a synchronous, periodic, or immediate feedback signal, although most or It can be any other type of communication link that provides a feedback signal without any delay.

  In a simple embodiment, the controller 100 can implement a single / input, single / output closed loop control routine, such as a PID control routine, which is one form of a PID type control routine. As used herein, PID type control routines are proportional (P), integral (I), derivative (D), proportional-integral (PI), proportional-derivative (PD), integral-derivative (ID). Or a proportional-integral-derivative (PID) control routine. Thus, the controller 100 includes a control signal generation unit having a summing block 108 that generates an error signal between the set point and the measured process variable, a proportional gain element 110, a further summing block 112, and a high and low limiter 114. , Including some standard PID controller elements. The control routine 100 also includes a direct feedback path that includes a filter 116. The filter 116 in this case receives the implicit actuator position signal and uses the high and low limiter 114 for use in calculating the reset (or other) control component of the control signal generated by the process controller 100. It can be coupled to the output or can be coupled to the actuator 102 as illustrated in FIG. Generally speaking, the output of the filter 116 is connected to an adder 112 that adds a reset (integral) component generated by the filter 116 to a proportional component generated by the gain unit 110. In addition, as illustrated in FIG. 4, the controller 100 can include a derivative component calculation block 132 that receives an error signal from the summing block 108 simultaneously with elements dedicated to calculating proportional and integral contributions. Here, the adder 134 adds the differential component of the control signal to the output of the adder 112 to generate a PID control signal having proportional, differential, and integral components. Of course, if desired, adders 112 and 134 can be combined into a single unit. In addition, other PID configurations (eg, series configurations) can be utilized, but proportional, integral, and derivative contributions can be combined in summing blocks 112 and 134 to generate non-limiting control signals. Illustrated.

More specifically, during operation of the controller 100, the summing block 108 compares the setpoint signal with the process variable measurements provided from the transmitter 106 just received to generate an error signal. . Proportional gain element 110 to generate a proportional contribution or component of the control signal, for example, by multiplying the proportional gain value K _p to the error signal, operating on the error signal. The summing block 112 then combines the output of the gain element 110 (ie, the proportional contribution) with the integral or reset contribution or component of the control signal generated by the feedback path, specifically by the filter 116. Adder 134 adds the derivative component generated by block 132 to generate a non-limiting control signal. The limiter block 114 then places a high and low limit on the output of the adder 134 to generate a control signal 105 that is used to control the process 101, specifically the actuator 102.

  Further, as illustrated in FIG. 4, the filter 116 is from the actuator 102 via a wireless communication link (which can be the same link 103 used to communicate control signals to the actuator 102). Concatenated to receive implicit positions. Filter 106 uses this implicit position value to determine the reset (integral) component of control signal 105 in the manner discussed in more detail below. Generally speaking, valve position feedback (ie, implicit) sent back to the controller 100 by the wireless actuator / valve 102 when communication between the controller 100 and the wireless valve or actuator 102 introduces a minimum delay. Can be used in a positive feedback network (ie, in filter 116) to create a reset contribution for PID controller 100. Here, if communication with the wireless valve 102 is lost or not updated in a periodic manner, the last target valve position communicated by the wireless valve or actuator 102 (i.e., the valve actuator 102 will work to achieve). The last known target position) feedback is used as the implicit position, which is the input to the continuously updated filter 116.

  Significantly, as illustrated in FIG. 4, the control routine implemented by the controller 100 also includes a control communication block 135 that significantly increases the transmission of control signals to the controlled device. Minimizing the number of changes made at the target position used by or provided to the actuator 102 when control is implemented using a radio valve or any other communication network that causes a significant delay Can be used to Specifically, in order to minimize the number of control signals transmitted to the actuator 102, thereby minimizing the power consumed by the valve actuator 102, the block 135, when certain criteria are met, It only transmits the calculated controller output or control signal 105 (as generated by the control routine in a periodic manner) to the wireless actuator 102. In a general sense, the use of these criteria reduces or minimizes the number of control signal changes sent to the actuator 102 while still providing robust control of the process.

  Generally speaking, the PID controller 100 is typically scheduled to run at a rate much faster than the highest rate at which the actuator 102 target value is communicated to the wireless actuator 102 using block 135. . More specifically, block 135 communicates an acknowledgment communication of the actuator to the last change in the target position where the time since the last communication sent to the wireless actuator 102 is greater than or equal to the configured communication period. If it is received at, the new value of the control signal 105 is only sent to the actuator 102. If desired, the configured communication cycle can be less than or equal to the execution rate of the communication block 135 that performs communication with the controlled device, so that the operation or execution of the communication block 135 has passed the configured communication cycle. (Ie, the elapsed time since the previous control signal was sent to the controlled device is longer than the minimum time threshold). In any case, if these conditions are met, the block 135 sets a new target position (ie, a new or updated control signal 105) when either or both of the two additional signaling criteria are met. Transmit to the actuator 102. Specifically, the absolute value of the difference between the newly calculated control signal and the last control signal communicated to the actuator 102 exceeds a configured deadband value (ie, threshold) and / or to the actuator 102. If the time since the last communication exceeds the configured default reporting time, the control communication block 135 communicates the newly calculated control signal 105 to the actuator 102. When these conditions are not satisfied, the control communication block 135 does not transmit the newly calculated control signal 105 to the actuator 102.

  Thus, generally speaking, the routine performed by the control communication block 135 is at most once per configured communication period (typically set to a controller execution period or higher) and the controller is The control signal is only transmitted when an acknowledgment that the actuator has actually received the last control signal transmitted to is received. The default setting for this condition is that the controller sends a control signal without exceeding a specific rate, and the actuator receives a previous control signal (as determined by the actuator's acknowledgment of a previously sent control signal). If not, it is guaranteed that no new control signal will be transmitted. Furthermore, these conditions are met (ie, the time since the last control signal was sent to the actuator 102 is longer than the configured or preset time, and the actuator 102 acknowledges receipt of the last control signal). If the new control signal magnitude differs from the previously transmitted control signal magnitude by a predetermined threshold, and / or the time since the last communication to the actuator 102 is the configured default reporting time. A new control signal is transmitted only when the value is exceeded.

  Thus, the communication block 135 confirms that a previous control signal has been received by the actuator 102 and a certain minimum amount of time has elapsed since the last control signal (determined by the configured communication period) has been transmitted. Only when the magnitude of the new control signal transmitted and the magnitude of the control signal just received differ by a certain threshold amount, or (the difference in control signal magnitude is a threshold value). It ensures that a new control signal is sent to the actuator 102 only if the time since the last control signal was sent and the current time exceeds a certain threshold (even if not the case). This operation generally reduces the number of control signals sent to the actuator 102 so as to reduce the number of actuator movements required by the controller, but in a manner that allows for robust control in the process. To reduce.

  Further, if desired, the valve target position communicated to the wireless actuator 102 by the block 135 as part of the control signal is usually the output calculated by the control routine (ie, the value of the previous control signal 105). Can do. However, as an option, the magnitude of the change in the target position (ie, the magnitude of the change in the control signal during the communication of successive control signals to the actuator 102) is the maximum change with the last communicated control value or target value. It can be restricted to add or subtract values. Therefore, if the absolute value of the control signal change between the new control signal and the last communicated control signal exceeds the configured maximum change value, the newly transmitted control signal (or target value) Limited to signal values with changes. In this manner, the control communication block 135 can limit the amount of change in the control signal between successive control signal communications to the actuator 102. Such limiting action is desirable when the last communicated control signal feedback or acknowledgment experiences significant delays to prevent large jumps in the control signal that may lead to poorer control performance. obtain.

  The advantage of this communication method is that the last communicated control value or target position feedback (ie, the implicit actuator position) provided by the wireless actuator 102 to the controller 100 is communicated with minimal delay. This value can be used in a positive feedback network to calculate the PID reset component (eg, by filter 116). This action automatically compensates for any delays or variations introduced by communication to the wireless actuator 102, thereby compensating for the delay in communicating the target position to the valve during PID adjustment. Does not require any change. As a result, the adjustment of the PID controller is strictly established by the gain and dynamics of the process, regardless of the delay introduced by the communication.

  More specifically, using the control communication routine described above still allows the filter 116 to provide robust control of the process while simultaneously communicating between the controller 100 and the actuator 102. It is possible to operate to generate an integral or reset contribution component of the control signal in a reduced manner. Specifically, the filter 116 coupled to receive an implicit actuator position (e.g., transmitted from the actuator 102 via a wireless communication path) includes the implicit actuator position and the execution period or time of the control algorithm 100. To generate an indication of the expected process response to the control signal 105. In this case, the implicit actuator position can be the control signal just received by the actuator 102 (or the target position of the previous control signal), which indicates the position where the actuator 102 moves. When executed, the filter 116 provides the expected process response signal to the adder 112, as illustrated in FIG. If desired, the expected process response to changes in the output of summer 108 generated by filter 116 can be approximated using a first order model, as described in more detail below. More generally, however, the expected process response can be generated using any suitable model of process 101 and the process associated with determining the integral or reset contribution of the control signal. Not limited to models. For example, a controller that utilizes a process model to provide an expected process response may or may not incorporate a derivative contribution so that the control routine 100 can implement a PID or PI control scheme.

Before discussing the operation of the filter 116 of FIG. 4 in more detail, it is useful to note that a conventional PI controller can be implemented using a positive feedback network to determine the integration or reset contribution. is there. Mathematically, it can be shown that the transfer function for conventional PI implementation is equivalent to the development of a standard for control that is unconstrained, ie, the output is not limited. In particular:

As illustrated in FIG. 4, one advantage of using a positive feedback path from the actuator 102 to provide an implicit actuator position is that when the controller output is high or low limited by the limiter 114. In addition, the reset contribution is automatically prevented from ending.

  In any case, the control techniques described herein can use a positive feedback path to determine the reset contribution when the controller receives a periodic or aperiodic update of a process variable. While still allowing a robust controller response in the event of a setpoint change or feedforward change that occurs during receipt of a new process variable measurement, while also allowing the process control loop to operate Limit the number of actuator movements. Specifically, in order to provide robust setpoint change behavior, the filter 116 may calculate a new indication or value of the expected process response during each run of the controller 100 or from run to run. Composed. As a result, the output of filter 116 is newly regenerated during each execution cycle of the control routine, even if the input to filter 116 (implicit position of actuator 102) is not updated on such a periodic basis. .

In general, the new indication of the predicted process response as generated by the filter 116 is the implicit actuator position, the prediction generated by the filter 116 generated during the last (ie, immediately preceding) controller run cycle. It is calculated during each controller execution cycle from the response instruction and the controller execution cycle. As a result, filter 116 is described herein as continuously updated as it is executed during each controller run cycle to generate a new process response estimate. An exemplary equation that can be implemented by continuously updated filter 116 to generate a new expected process response or filter during each controller run cycle is described below.

Here, the new filter output F _N is equal to the previous filter output F _N−1 (that is, the current filter output value), or the controller output value immediately before received by the actuator O _N−1 (implicit actuator value) (or The target position) and the current filter output value _FN−1 are multiplied by a factor that depends on the reset time T _Reset and the controller execution period ΔT, and iteratively You will notice that it is decided.

  Using a filter that continuously updates in this manner, the control routine 100 better determines the expected process response when calculating the integral control signal component each time a new process variable measurement is received. Can be made more sensitive to setpoint changes or other feedforward disturbances that occur during the reception of two process variable measurements. More specifically, a change in the set point (without the receipt of a new process measurement) changes the proportional contribution component of the control signal, thus changing the control signal, the error signal at the output of the adder 108. You will notice that this change will happen immediately. As a result, filter 116 immediately begins to generate a new expected response of the process to the changed control signal, and thus its output before controller 100 receives a new process measurement that is measured in response to the change. Can be updated. When the controller 100 receives a new process measurement and the sample of the filter output is then clamped to the input of the adder 112 for use as an integral or reset contribution component of the control signal, the filter 116 At least in part, it repeats the expected process response in response to, or incorporated in, the process 101 response to a set point change.

  Thus, as is well understood, the control technique illustrated in FIG. 4 is expected through a continuously updated filter 116 (eg, a reset contribution filter) for each execution of the control block or routine 100. Process response instructions are calculated. In the embodiment of FIG. 4, the controller 100 configures a continuously updated filter 116 to calculate a new indication of expected response for each execution of the control block. Thus, the continuously updated filter 116 continues to calculate an expected response indication for each iteration of the control routine based on the implicit actuator position (eg, the control signal received immediately prior to the actuator 102). This new expected response indication is delivered to summing block 112 during each execution cycle.

  This control technique is a continuously updated filter 116 regardless of whether new measurements are communicated and without having to determine whether to send the current controller output to the actuator 102. Makes it possible to continue to model the expected process response. If the control output changes as a result of a feed-forward action based on a set point change or a measured disturbance, the continuously updated filter 116 will repeat each control routine based on the implicit position of the actuator 102. Correctly reflects the expected process response by calculating a new indication of the expected response.

  The simple PID controller configuration of FIG. 4 directly uses the output of the filter 116 as a reset contribution to the control signal, and in this case the reset contribution of the closed loop control routine (eg, the continuously updated presented above). Note that the filter equation) can provide an accurate representation of the process response in determining whether the process exhibits steady state behavior. However, other processes, such as dead time dominant processes, may require the incorporation of additional components of the controller of FIG. 4 to model the expected process response. For processes that are well represented by a first order model, the process time constant can generally be used to determine the reset time of the PI (or PID) controller. More specifically, if the reset time is set equal to the process time constant, the reset contribution generally overrides the proportional contribution so that the control routine 100 reflects the expected process response over time. . In the example illustrated in FIG. 4, the reset contribution can be achieved by a positive feedback network with a filter 116 having a time constant that is the same as the process time constant. While other models can be utilized, a positive feedback network, filter, or model provides a convenient mechanism for determining the expected response of a process having a known or approximate process time constant.

  5 and 6 provide robust control in response to set point changes, while also communicating control described above with respect to FIG. 4 to minimize controller movement in the controlled device. And some other embodiments of control systems that can use filtering techniques. Specifically, in some applications, various different combinations of wired or wireless transmitters or sensors and wired or wireless controlled devices such as valves may be used in the control scheme. More specifically, in a control loop that includes a wireless transmitter and a wired valve or actuator, such as in a control loop that includes a wired transmitter and a wireless valve or actuator (as illustrated in FIG. 4). Or, it may be desirable to implement the control techniques described above to minimize controller movement in a control loop that includes an actuator and / or in a control loop that includes a wired transmitter and a wired valve or actuator. is there. Here, the wireless communication path of the embodiments described herein may be slow, intermittent, asynchronous, between the controller and the actuator and / or between the transmitter (sensor) and the controller, It is envisaged that these communication networks or control systems are essentially the same concept or control technique described herein for these networks, and that it is envisaged to introduce aperiodic and / or significantly delayed transmissions. It will be appreciated that even if not wireless, it can be applied to a control system having any communication network having one or more of these characteristics.

  FIG. 5 illustrates one embodiment of a control system 500 or control loop that includes both a wireless transmitter (and thereby a wireless feedback communication path) and a wireless valve or actuator (and thereby a wireless control signal communication path). Significant delays, lost signals, aperiodic or asynchronous communications are considered to be introduced by one or both of these wireless communication paths. The control system 500 illustrated in FIG. 5 is essentially similar to the control system of FIG. 4, but the controller 100 of FIG. 5 may cause a potential delay or loss of communication and / or the sensor 106 and the controller 100. Except to include additional control elements that need to deal with the loss of synchronous or periodic communication in the feedback communication path between. As will be appreciated, this path is now shown as a dotted line in FIG. 5 to indicate that this communication path is wireless, aperiodic, asynchronous, and / or exhibits significant delay. .

  As illustrated in FIG. 5, the controller 100 includes a control signal generation unit having an addition block 108, a proportional gain element 110, a further addition block 112, a derivative calculation block 132, a still further addition block 134, and a high / low limiter 114. Including the standard PID controller elements described above with respect to FIG. The control routine 100 also includes a feedback path that includes the filter 116, but in this case, additionally includes an integration output switch that includes the communication stack 80 and a selection block 118 coupled to the filter 116. As illustrated in FIG. 5, the filter 116 is still coupled to receive the implicit actuator position, but at this point it provides the output of the filter 116 to the block 118, and then by the controller 100. An integral or reset component of the generated control signal is provided to summing block 112.

During operation of the controller 100, the summing block 108 compares the setpoint signal with the last received process variable measurement (provided from the communication stack 80 in the controller 100) to generate an error signal. . Proportional gain element 110 to generate a proportional contribution or component of the control signal, for example, by multiplying the proportional gain value K _p to the error signal, operating on the error signal. The summing block 112 then combines the output of the gain element 110 (ie, the proportional contribution) with the integral or reset contribution or component of the control signal generated by the feedback path (including the filter 116 and block 118). The differential component block 132 operates on the output (error signal) of the adder 108 to generate a differential component of the control signal that is added by the adder 134 to the output of the adder 112. The limiter block 114 then places a high and low limit on the output of the adder 134 to generate a control signal 105 that is provided to the control communication block 135. Block 135 is in the manner described above with respect to FIG. 4 to determine when to send a new control signal 105 to actuator 102 via wireless link 103 (which may experience significant delay). Operate.

  In this case, the filter 116 and block or switch 118 in the feedback path of the controller 100 operate to generate an integral or reset contribution component of the control signal in the following manner. A filter 116 coupled to receive the output of the limiter 114 is expected for the control signal 105 based on the implicit actuator position and the execution period or time of the control algorithm 100, as described above with respect to FIG. Generate a process response indication. However, in this case, the filter 116 provides this expected process response signal to the switch or block 118. Each time the controller 100 receives a new process variable measurement (determined by the communication stack 80), the switch or block 118 samples and clamps the output of the filter 116 at the output of the switch or block 118, and the communication stack 80 This value is maintained until the next process variable measurement is received. In this way, the output of switch 118 remains the output of filter 116 that was generated when controller 100 received the last process variable measurement update.

  More specifically, the control technique illustrated in FIG. 5 provides for the expected response of each execution of the control block or routine 100 through a continuously updated filter 116 (eg, a reset contribution filter). Calculate the instructions. However, to determine whether the output of filter 116 should be used as an input to summing block 112, communication stack 80 and, in some embodiments, update detection module 82 (FIG. 3) When a new process variable measurement is received, the incoming data from transmitter 106 is processed to generate a new value flag for integral output switch 118. This new value flag informs switch 118 to sample and clamp the output of filter 116 for this controller iteration and provide this value to the input of adder 112.

  Regardless of whether a new value flag is communicated, the continuously updated filter 116 continues to calculate an expected response indication for each iteration of the control routine. This new indication of expected response is delivered to the integral output switch or block 118 of each execution of the control block. In response to the presence of the new value flag, the integral output switch 118 allows the expected response from the continuously updated filter 116 to pass the new indication to the summing block 112 and the final control block. Between maintaining a signal previously delivered to summing block 112 during the execution of. More specifically, when a new value flag is communicated, the integral output switch 118 passes an indication of the expected response just calculated from the continuously updated filter 116 to the summing block 112. Make it possible. Conversely, if there is no new value flag, the integration output switch 118 retransmits an indication of the expected response from the last control block iteration to the summing block 112. In this manner, the integral output switch 118 clamps to a new indication of the expected response each time a new value flag is communicated from the stack 80, but is generated by the filter 116 if no new value flag exists. Also, any indication of the newly calculated expected response does not allow the summing block 112 to be reached.

  Thus, as will be appreciated, the use of block 118 allows continuously updated filter 116 to continue to model the expected process response, regardless of whether new measurements are communicated. To do. If the control output changes as a result of a feed-forward action based on a set point change or a measured disturbance, the continuously updated filter 116 is repeated at each control routine iteration, regardless of the presence of a new value flag. Correctly reflects the expected process response by calculating a new indication of the expected response. However, a new indication of the expected response (ie reset contribution or integral component) is only incorporated into the controller calculation when a new value flag is communicated (via the integral output switch 118).

  Thus, generally speaking, the control routine 100 of FIG. 5 generates an expected process response by based on the aperiodic, delayed or asynchronous measurements received at the communication stack 80, and On the other hand, in addition, it is expected between the reception of two measurements to compensate for changes caused by changes in the set point, or any measured disturbance used as a feedforward input to the controller 100. Determine the response. In this way, the control techniques described above can be adapted to setpoint changes, feedforward actions on measured disturbances, etc. that can affect the expected process response, and thus at the controller 100 A more robust control response can be provided in the presence of communication delays associated with both communication of control signals to the actuator 102 and feedback or reception of measured process variable signals.

  Further, as shown in FIG. 5, the communication stack 80 provides the adder 108 with the feedback signal just received, for use in calculating the error signal at the output of the adder 108. As also illustrated in FIG. 5, a new value flag generated by the communication stack 80 is also provided to the derivative calculation unit 132, which must be recalculated or operated to generate the derivative control component. Can be used to indicate what must be done. For example, the derivative contribution block 132 can be reconfigured to be based on the elapsed time since the last measurement update. In this manner, spikes in the differential contribution (and the resulting output signal) are avoided.

More specifically, as indicated by a new value flag from communication stack 80 to accommodate unreliable or delayed transmission in the feedback communication path, and more generally, no measurement update is available. The differential contribution can be maintained at the last determined value until a measurement update is received. This technique allows the control routine to continue periodic execution according to the normal or established execution rate of the control routine. Upon receipt of the updated measurement, the differentiation block 132 can determine the derivative contribution according to the following equation, as illustrated in FIG.

In the technique for determining this differential contribution, measurement updates to process variables (ie, control inputs) can be lost over one or more execution cycles without generating output spikes. When communication is reestablished, the differential contribution equation term (e _N −e _N−1 ) may produce the same value as that generated in the standard calculation of the differential contribution. However, for standard PID techniques, the divisor in determining the differential contribution is the execution period. In contrast, the control techniques described herein utilize the elapsed time between two successfully received measurements. With an elapsed time longer than the run period, the present control technique produces a smaller differential contribution than the standard PID technique, reducing spikes.

  To facilitate the determination of the elapsed time, the communication stack 80 sets the new value flag described above to the derivative block, as shown in FIG. 5, along with the elapsed time between the two previous received values. 132 can be provided. Furthermore, process measurements can be used instead of errors in the calculation of the proportional or derivative component. More generally, the communication stack 80 can be any software, hardware, or to implement a communication interface with the process 101, including any field devices within the process 101, process control elements external to the controller, etc. , Firmware (or any combination thereof) can be included or incorporated.

  As a further example, FIG. 6 implements the control communication block 135 as described above, but a wired communication path between the controller 100 and the actuator 102 and between the transmitter 106 and the controller 100 ( Or a process that is essentially similar to the process control system described above with respect to FIGS. 4 and 5 in that it is implemented in a control system configuration that includes other synchronous, periodic, or non-delayed communication paths). The control system 600 is illustrated. In the system of FIG. 6, the continuously updated filter 116 can be connected directly to receive the implicit actuator value and can be connected to provide its output directly to the adder 112. it can. Furthermore, process variable measurements from transmitter 106 can be directly connected to summer 108. Here, the control communication block 135 can be provided to reduce the number of controller updates (control signals) sent to the actuator 102 to reduce actuator movement. Thus, as illustrated in FIG. 6, the control communication block 135 eliminates the “hunting” phenomenon seen in many situations, even when synchronous, periodic, or non-delayed control and feedback communication is present. To reduce and to reduce other excessive movement of the actuator 102, it can operate in the manner described above in a wired or non-delayed communication network. In yet another example not illustrated in the figure, the control communication block 135 may be used to communicate wirelessly (and thus potentially slow, asynchronous, delayed, or aperiodic communication) between the transmitter or sensor and the controller. Can be used in situations where wired (or synchronous, periodic, or non-delayed) communication is provided between the controller and the actuator in the control loop.

    In addition, although the control communication block 135 is illustrated as being in the controller block 100, the control communication block 135 (or the function associated therewith) is responsible for the controller output and the aperiodic controller generated by the block 135. It can be implemented at any point between the controlled device receiving the output. For example, block 135 can be incorporated into the control loop or at any point along the control signal path after calculating the PID output and before receiving this signal at the actuator or other controlled device. For example, the non-periodic control communication of block 135 is to the output block according to the PID controller at the gateway device or at any other device located in the control signal communication path between the controller and the actuator being controlled. Can be incorporated. If desired, this function can be performed even in the actuator itself.

  The key to utilizing the aperiodic control communication block 135 as described herein is to use a positive feedback network based on the implicit valve position that is then communicated from the actuator to the controller, preferably with minimal delay Then, PID reset calculation is performed. Ideally, implicit valve position feedback (ie, the target position that the valve actuator is accepting and operating to achieve) is sent back to the wireless gateway by the wireless actuator in response to the target position write request. . Such a system is illustrated in FIG. Specifically, as illustrated in FIG. 7, during operation, the control communication block 135 is routed over a wireless path (eg, a delayed or asynchronous communication link), as illustrated by dashed line 200a. A write request including a new control target is transmitted to the wireless actuator 102. Subsequently, when the wireless actuator 102 receives a new control signal or target, the wireless actuator 102 is wireless (as illustrated by dashed line 200b) with a write response indicating that the actuator 102 has received the control signal. Respond to block 135 (via a link). The write response is basically an acknowledgment of reception of the control signal. Further, the write response (to the write request) can reflect the accepted control or target value. Upon receipt of the write response, block 135 can change the implicit actuator position to the position indicated by the control signal transmitted in the write request or by the accepted target value indicated in the write response. Thus, the control block 135 can be involved in sending the implicit actuator position to the filter 116 of FIGS. 4-6 for use as the implicit actuator position. Of course, any device in the communication link between the controller and the actuator, such as a gateway device (eg, gateway 73 in FIG. 3), is used to implement the write request or acknowledgment in the form of a write response. Can do.

  In some implementations of wireless communication, there is a significant delay between the actuator 102 that receives the command to change the target position and the actuator response that is returned to the controller (or block 135) and that the controller can access. May exist. In this case, the controller is restricted from sending a new control signal until after receiving an acknowledgment from the actuator by the action of block 135. To enable the controller 100 to automatically compensate for this significant and varying delay in write response wireless communication, a new control signal data format is used to enable wireless actuators such as wireless valve actuators. The control used can be supported.

  Specifically, when transmitting the control output value to the wireless actuator, a time field until application can be added to the control signal. This field can specify a future time when the output value must be enforced or executed by the actuator. Preferably, the delay time should be set so that both the output communication to the actuator and the readback communication to the controller are completed before this future time. In other words, the future time at which the actuator performs the change to effect the movement to the control signal target value is preferably the communication of the new control signal to the actuator by block 135 and / or from the actuator to block 135 or The time is greater than the expected delay introduced into the communication by one or both of acknowledgment or write response communication to the controller 100. However, using this command, the implicit actuator position can be accurately determined based on the target position communicated to the actuator and the time that specifies when the actuator must act on the new target position. Enable to calculate. For example, if the time specified in the output is always a fixed number of seconds Y in the future, the implicit actuator (or valve) position simply delays the target position by Y seconds, thereby causing the controller 100, gateway, etc. Can be calculated. Thus, the calculated implicit actuator position is used to communicate the new target position to the actuator with the delay time specified in the new command (and possibly to receive an acknowledgment that the target has been received from the actuator). B) If the required time is exceeded, the target value used by the actuator is met. In order to ensure that the calculated implicit actuator position accurately reflects the target position of the actuator, a new output can be issued to the actuator only when the last communication confirmation is received.

  Thus, generally speaking, the new command can include one or more new target value (s) and time (s) that the actuator or valve must take action on the new request. . In this case, when a new request is received, the valve or actuator waits until a scheduled time for taking action on the new target value (s). However, when a valve or actuator receives a new command, even before the valve takes action on the new target value (s) (so as to confirm receipt and change the new implicit actuator position). Attempt to send a response immediately (to generate) with an acknowledgment and / or with new target value (s). This command alleviates or alleviates the problems associated with block 135 (or controller using filter 116) receiving implicit actuator position values that are significantly delayed, and is therefore good in these situations. Provide complete control. In fact, to minimize the impact of this communication delay, using such new commands when controlling with a wireless valve, and the implicit actuator position used in the controller's feedback loop, Based on the target value sent to, it is proposed to delay by a time between the time of action in the command and the time buffered to send the new target value to the valve. Thus, the external reset value used in the controller can be calculated at the communication layer or control module, and “implicit valve position for use as a PID external reset value (eg, as an input to the filter 116). Can be provided. In either case, however, it is desirable to wait for a new control command to be issued until the valve or actuator receives confirmation from the valve that it has received a previous command sent to the valve.

  Of course, the time value used in this command can be based on the time the new target value was accepted in block 135 plus a preconfigured delay time. The delay time can be set by, for example, a user, a configuration engineer, a manufacturer, or the like, or statistical characteristics of the communication link (eg, average delay measured or observed in the communication link over a specific period, central delay) , Maximum delay, one or more standard deviations of expected delay based on multiple delay measurements, etc.).

  As an example of the operation of such a command, FIG. 8 is processed so that the AO output block generates a control signal having a new target value, the new target value is communicated to the valve (or actuator), and then the valve or Illustrated is a timing diagram 800 of various signals involved in a communication procedure acted upon by an actuator. In the example of FIG. 8, line 801 represents a control signal developed by the control routine and provided as input to the control communication block 135. Line 802 represents the generation of a target output or output control signal provided to the actuator by control communication block 135. Line 804 represents the receipt of a new target value at the actuator and may correspond to a return of the target value acknowledgment receipt by the actuator (valve) to the controller. Line 806 represents the timing of the operation of the actuator or valve in response to the control signal and illustrates the delay time of the control signal that is longer than the time it takes for the target value change on line 802 to reach the actuator. . The last line 808 represents the latest valve response received by block 135. Block 135 does not issue a new or changed control signal until the actuator (valve) receives a write response indicating that it has received a previous control signal, due to the operations described above, and therefore Note that the change in line 808 corresponds in time (or nearly in time) to the change in issuance of a new signal from block 135 (indicated by line 802).

  In any case, using this delay time as part of the control signal means that if the controller has a significant communication delay between the controller and the actuator, the actuator will actually Changing the implicit actuator position used in the calculation of feedback (eg, with the filter 116 described above) at or near the same time as acting on the control signal to move toward Enable. This operation more closely synchronizes the calculation of the control feedback and the actual operation of the valve, thereby providing a better or more robust control operation.

Table I below provides an example of a WirelessHART custom command definition defined for radio location monitoring that implements this delay time concept. The command illustrated in Table I writes one or more output values (defined in bytes 3 and 4 for one or more parameters identified in bytes 0 and 1) to a monitor (eg, actuator). , And also includes a time field to apply (to bytes 6-13). The time to apply field is synchronized across different devices in the process control communication network, offset or delay time from some specified time stamp (eg, time stamp associated with transmission of control signal from block 135) The absolute time determined by the system clock that can be used, the offset time from the system clock, etc. can be indicated. Further, if desired, the new command can transmit multiple control signals that are applied simultaneously or sequentially at different offset times or at the same offset time. The number of commands can be provided in the second byte, for example, as shown in Table I.

Table I

  In any case, as long as the control system and the wireless network have a common sense or measurement of time for this command, and the delay time specified in the command is longer than the one-way or round-trip delay of the write request and response. For example, using this data format for valve or other actuator control would result in zero or equivalent readback or acknowledgment delay.

  To demonstrate the functionality of the control and communication systems described herein, two sets of tests were performed. The first set of tests is performed assuming a minimum response (acknowledgment) delay, and the second set of tests is based on the concept of time to application as part of the control signal, as explained above. Made to include a significant response delay, relaxed using. Each test described herein was performed using a simulated process control system.

In a set of tests using minimum response delay, in order to demonstrate that PID control using aperiodic communication to a wireless valve is an effective means to reduce the number of communications to the valve, in total Eight tests were performed. Control, communication, and process response simulations allow the performance of a control system with aperiodic control communication sent to a wireless valve to be compared to a conventional PID control system that uses a wireless valve. Created. In these tests, communication from the controller to the valve included a significant delay, but confirmation that the valve received the message was received with minimal delay. Process gain and dynamics, and PID adjustment were the same for these eight tests and were used as follows.

Process PID adjustment gain = 1 Gain = 1
Time constant = 6 seconds Reset = 8 seconds / Repeat DT = 2 seconds Rate = 0

Each of these tests introduced the same set point change (10%) and unmeasured load disturbance change (10%). The test conditions are summarized in Table II.

Table II

The results of these tests are summarized in Table III.

* Use of wireless transmitter with wireless valve Table III

  By using the proposed changes to the PID as shown in Table III (ie, the reset calculation uses aperiodic communication for the radio valve based on the implicit valve position communicated by the radio valve ) The number of communications to the valve has been greatly reduced. In most cases, control performance was still acceptable. The response during test 4 is illustrated in graph 900 of FIG. 9 and is typical of the responses seen during these tests. Specifically, the first set of lines in the graph 900 is a setpoint value 901, a measured controlled value obtained using a wireless valve (according to the control and communication procedures described herein). Variable 902 and measured controlled variable 903 (and a typical PID control routine) obtained using a wired valve are shown. The second set of lines is the valve movement or valve position 910 for wireless valves (using the control and communication procedures described herein), and the valve for wired valves (using a typical PID control routine). Position 911 is shown. The lower line 915 is an unmeasured disturbance introduced for simulation purposes. Thus, the graph 900 shows the comparative performance of the process control loop using the control and communication procedures described herein with respect to Test 4 in response to both set point changes and unmeasured disturbances in the process. .

  In addition, as a further test, the control and communication simulations performed in some of the tests described above can be performed with significant communication delays between the controller and the valve, and significant delays in valve response or acknowledgment communication. Modified to use new control signal data format to enable. Tests 9-12 were performed using this modified simulation that included significant communication delays in the feedback path between the actuator and the controller. These additional tests used the same process gain and dynamics and controller adjustments used in previous tests.

In Test 9 and Test 10, the wired measurement and the wireless valve are compared with the wired measurement and the wired valve. In Test 11 and Test 12, a wireless measurement value having a wireless valve is compared with a wired measurement value and a wired valve. During these tests, the same changes in set point and unmeasured disturbance were introduced into both control loops. The aperiodic communication setup to minimize valve movement, the communication delay for the valve, and the communication delay in the valve response are shown in Table IV.

Table IV

Table V summarizes the results achieved for the relationship between wireless control using modifications to the wireless valve and wired transmitters and valves using typical PID control.

Table V

  The test results show that the effect of communication delay can be minimized by using the proposed new output data signal format in conjunction with the implicit valve position calculated for the external reset. Stable control was observed for set point changes and load disturbances using wireless valves. The number of valve target changes has been reduced by a factor of 23. The responses during test 10 are illustrated in graph 1000 of FIG. 10 and are typical of the responses seen during these tests. The first set of lines in the graph 1000 uses set point values 1001, controlled variables 1002 measured using wireless valves (according to the control and communication procedures described herein), and wired valves. The controlled variable 1003 (and a typical PID control routine). The second set of lines are valve movement or valve position 1010 for wireless valves (according to the control and communication procedures described herein) and valve position 1011 for wired valves (using a typical PID control routine). Indicates. The lower line 1015 is an unmeasured disturbance. Thus, the graph 1000 shows the comparative performance of the process control loop using the control and communication procedures described herein with respect to test 10 in response to both set point changes and unmeasured disturbances in the process. .

    In another experiment, a WirelessHART network was simulated using a laboratory-set WirelessHART module to act as both a sensor and an actuator. The simulated process was performed inside the module to correlate sensor and actuator values. Since an actual wireless network was used, this experiment is considered to closely represent the actual application.

  To better understand this experiment, the relevant components of a DCS (Distributed Control System) with a WirelessHART network and the modifications made to perform the experiment are described. Specifically, the test DCS included a WirelessHART network using all WirelessHART devices that were input devices. The device issued data to the gateway, which cached the data upon request and forwarded the data to the host. In the DCS system used, the component that communicates with the gateway was called PIO. A control module containing the PID communicated with the PIO. Whenever the gateway could not send the requested response, it immediately responded to any other request from the PIO with a delayed response (DR) status. The gateway then forwarded this request to the controlled device in the WirelessHART network. Thus, until the response from the controlled device was received by the gateway, and then finally responded without a DR signal, the PIO had to repeatedly query the gateway and repeatedly obtain the DR. This mechanism was applied to output writing to the actuator. However, future WirelessHART standards may allow negative response requests from the PIO to the device, ie downstream issue.

Control communication components similar to those described above for block 135 were implemented in the PIO of this experiment. In addition, the HART write command was used to write the output to the valve using the time-to-apply concept described above. Therefore, the target valve position maintained by the radio valve was changed using a HART command with a delay component or a time component to apply. If the target valve position specified in the command was different from the valve position included in the previous change request issued to the gateway, this command was considered a new request. If the gateway had previously received a radio valve response to the last requested position change, it acted on the new change request. Otherwise, a new change request was buffered by the gateway. In order to ensure that the latest PID output is used and communicated to the valve with minimal delay, the aperiodic communication performed by the controller (PIO block) was designed to observe the following conditions:
(1) The new target value was communicated to the valve and the PID block was executed much faster than the time required for the gateway to receive a response.
(2) Each time PID is executed (at least once per second), a change request command is sent to the PIO. However, if the same command (same target value) was sent to the PIO, the associated valve response was returned. The associated target value was reflected in the READ_BACK parameter of the AO block.
(3) When the status of the READ_BACK parameter of the AO block changes to a defective communication failure, the same change request is continuously transmitted to the gateway and is regarded as a new command.

A communication diagram illustrating the change in PID output after application of the aperiodic control communication block in this experiment is illustrated in Table VI.


Table VI

  As illustrated in Table VI, in Step 2, a new change request was issued by the controller AO / Out block and by the PIO to change the valve target to 50. The gateway's immediate response was a response with a DR (Delayed Response) signal. One second later, in step 4, the same change request was issued again to the gateway. The gateway then issued a HART command to the valve at step 6 (to change the valve target at the valve) but did not receive a response (write response) until step 9. However, in step 8, after the delay time provided to the valve in the original control command, the change request was reflected in the AO / READBACK value for use in the controller's PID positive feedback network as an implicit valve position. In step 11 (in response to the control command reissued in step 10), the target valve position returned by the valve to the gateway (in step 9) was returned to the PIO. Thereafter, in step 12, a new change in PID output was issued by the PIO, all shown in Table VI.

  Assuming that the communication from the gateway to the valve is lost in the next step 6, the loss of the valve response has been detected by the gateway after a certain period of time, and this failure is in response to the next controller write request. Would have been shown. This failure would then be indicated by the AO / READBACK status changing to bad communication. The next controller write after detecting communication would then be treated as a new write request. However, the AO / READBACK would continue to indicate a bad communication status until a response from the valve was received in response to the repeated change request.

  In a general sense, the controller or PID modifications discussed above for control using wireless valves also make the wired valve to minimize valve wear by reducing the frequency of target valve position changes. It can also be applied to the PID controller used. To address such applications, aperiodic communication functions can be incorporated into the PID or IO function block, and the implicit valve position can be based on the control signal value output to the valve. Furthermore, the criteria used to determine whether the calculated PID output must be communicated to the radio valve can also include or take into account the rate at which the calculated control output is changing. In some cases, this feature allows for a faster response of unmeasured process disturbances. Still further, as part of the non-periodic control communication function described herein, before applying the control communication criteria discussed herein to determine whether a new control value must be communicated. In addition, filtering can be applied to the calculated control output. Similarly, a metric indicating the number of changes in valve position and total valve actuation amount, to determine the effect of non-periodic control communication in reducing the frequency of change in target valve position, wireless gateway, wireless valve, etc. Can be incorporated into any control system.

  In general, the control techniques practiced herein are not limited to use with single-input, single-output PID control routines (including P, PI, and PD routines) Rather, it can be applied in many different multiple input and / or multiple output control schemes, cascaded control schemes, or other control schemes. More generally, the control techniques described herein are also based on any closed-loop model that involves the use or generation of one or more process output variables, one or more process input variables, or other control signals. The present invention can also be applied to the situation of control routines such as model predictive control routines.

  The term “field device” as used herein refers to any device or combination of devices (ie, a device that provides multiple functions, such as a hybrid transmitter and actuator), as well as any function that performs a function in a control system. Used broadly to include other device (s). In any case, field devices include, for example, input devices (eg, devices such as sensors and equipment that provide status, measurements, or other signals indicating process control parameters such as temperature, pressure, flow rate) and controllers And / or may include a control operator or actuator that takes action in response to commands received from other field devices such as valves, switches, flow control devices, and the like.

  It should be noted that any control routine or module described herein may have a portion thereof that is implemented or executed in a distributed manner across multiple devices. As a result, the control routines or modules can have portions implemented by different controllers, field devices (eg, smart field devices) or other devices, or other control elements, as desired. Similarly, the control routines or modules described herein that are implemented within a process control system may take any form, including software, firmware, hardware, and the like. Any device or element involved in providing such functionality may be software, firmware, or hardware associated therewith, located on a controller, field device in a process control system, or any other In the present specification, it may be generally referred to as a “control element” regardless of whether it is disposed on a device (or a collection of devices). A control module, routine, or block is any part or portion of a process control system, including, for example, a routine, block, or any element thereof stored in any computer-readable medium and executed by a processor. can do. Such a control module, control routine, or any portion thereof (eg, a block) can be implemented or executed by any element or device of a process control system, generally referred to herein as a control element. . Control routines that can be modules or any part of a control procedure such as a subroutine, part of a subroutine (such as a series of code), using object-oriented programming, or ladder logic, sequential functions It can be implemented in any desired software format using charts, functional block diagrams, or using any other software programming language or design paradigm. Similarly, the control routine can be hardcoded into, for example, one or more EPROMs, EEPROMs, application specific integrated circuits (ASICs), or any other hardware or firmware element. Still further, the control routine can be designed using any design tool, including a graphical design tool, or any other type of software / hardware / firmware programming or design tool. Accordingly, the controller 11 described herein can be configured to implement a control strategy or control routine in any desired manner.

  Alternatively or additionally, the functional blocks can be stored and implemented by the field device itself or other control elements of the process control system, when the system utilizes a fieldbus device. obtain. The description of the control system is generally provided herein using a functional block control strategy, but the control techniques and systems may also use other rules such as ladder logic, sequential function charts, or Any other desired programming language or paradigm can be used or implemented.

  When implemented, any of the software described herein may be any computer readable memory, such as a magnetic disk, laser disk, or other storage medium, computer or processor RAM or ROM, flash memory, etc. Can be memorized. Similarly, the software includes a communication channel such as, for example, a computer readable disk or other portable computer storage mechanism, or a telephone line, the Internet, the World Wide Web, any other local area network or wide area network. Any known or desired delivery method can be used to deliver to a user, process plant, or operator workstation. In addition, the software can be provided directly without modulation or encryption, or can be modulated using any suitable modulated carrier and / or encryption technique before being transmitted over the communication channel. And / or can be encrypted.

  Thus, while the present invention has been described with reference to specific embodiments, which are intended to be illustrative only and not limiting, those skilled in the art will appreciate the spirit of the invention. It will be apparent that modifications, additions, or deletions may be made to the control techniques described herein without departing from the scope and scope.

Claims (61)

A method for controlling a controlled device in a process using a control signal, comprising:
Performing the multiple iterations of the control routine at a process controller computing device to generate a control signal value for controlling the controlled device during each of the multiple iterations;
During each of a number of iterations of the control routine,
Determining whether a predetermined minimum communication period has elapsed; and determining whether an acknowledgment has been received from the controlled device indicating that the controlled device has received a previous control signal;
Whether at least a further signaling condition is satisfied when the predetermined minimum communication period has elapsed and an acknowledgment is received from the controlled device indicating that the controlled device has received the previous control signal. To determine whether
When the predetermined minimum communication period has elapsed and an acknowledgment is received from the controlled device indicating that the controlled device has received the previous control signal, and the further signaling condition is satisfied Implementing a communication routine in a computer processing device coupled to the process controller computing device, the method comprising: transmitting a new control signal to the controlled device only over a communication link.   Determining whether the further signaling condition is satisfied is that a difference between the control signal value generated for repeating the control routine and the value of the previous control signal transmitted to the controlled device is a threshold value. The method of claim 1, comprising determining if greater than.   Determining whether the further signaling condition is satisfied includes determining whether a time since the previous control signal was transmitted to the controlled device exceeded a maximum threshold time value. Item 4. The method according to any one of Items 1 to 3.   Determining whether the further signaling condition is satisfied is that a difference between the control signal value generated for repeating the control routine and the value of the previous control signal transmitted to the controlled device is a threshold value. The method of claim 1, further comprising: determining whether the time is greater than or a time since the previous control signal was transmitted to the controlled device exceeds a maximum threshold time value. The method according to claim 1.   Implementing the communication routine in a computer processing device coupled to the process controller computing device includes performing the communication routine during each of a number of successive iterations of the control routine. The method as described in any one of Claims 1-4.   Sending a new signal over the communication link to the controlled device means that the difference between the control signal value for repeating the control routine and the value of the previous control signal sent to the controlled device is maximum. A difference between the control signal value for repeating the control routine and the value of the previous control signal transmitted to the controlled device is greater than the maximum change threshold value. 6. The method according to any one of claims 1 to 5, comprising transmitting the new control signal as a limited version of the control signal value for repeating the control routine when.   7. The method of claim 1, wherein transmitting the new control signal to the controlled device via a communication link includes transmitting the new control signal to the controlled device via a wireless communication link. The method according to one item.   7. The method of claim 1, wherein transmitting the new control signal to the controlled device via a communication link includes transmitting the new control signal to the controlled device via a wired communication link. The method according to one item.   Transmitting the new control signal to the controlled device via a communication link includes transmitting the new control signal as a new control signal value and time to implement the new control signal value on the controlled device. The method according to claim 1, comprising:   The method of claim 9, wherein transmitting the time to implement the new control signal value comprises transmitting the time as an offset time.   The method of claim 9, wherein transmitting the time to implement the new control signal value comprises transmitting the time as an absolute time.   12. A method according to any one of the preceding claims, wherein performing multiple iterations of a control routine on a process controller computing device comprises performing a proportional, integral, derivative type control routine. .   The method of claim 12, wherein performing the proportional, integral, derivative type control routine includes using a feedback signal indicative of an attribute of the controlled device to generate the control signal value. .   Transmitting the new control signal to the controlled device over a communication link includes transmitting a new control signal value and a predetermined time to implement the new control signal value at the controlled device; and a feedback signal Using the controlled device as having implemented the new control signal value at the predetermined time to implement the new control signal value to determine the feedback signal. Item 14. The method according to any one of Items 12 to 13.   15. The method according to any one of claims 13 to 14, further comprising receiving the feedback signal via a wireless communication link.   15. The method according to any one of claims 13 to 14, further comprising receiving the feedback signal via a wired communication link. A process control system for use in controlling a controlled device in a process using a control signal, comprising:
A process controller that stores the control routine and implements the control routine during the multiple iterations to generate a control signal value for controlling the controlled device during each of the multiple iterations;
A communication routine implemented in a computer processing device coupled to the process controller for receiving the generated control signal value for each of the multiple iterations of the control routine; and
To determine whether a predetermined minimum communication period has elapsed and to determine from the controlled device whether an acknowledgment has been received indicating that the controlled device has received a previous control signal Run,
Further, when at least the predetermined minimum communication period has elapsed and an acknowledgment is received from the controlled device indicating that the controlled device has received the previous control signal, a further signaling condition is set. Run to determine if it meets,
When the predetermined minimum communication period has elapsed and an acknowledgment is received from the controlled device indicating that the controlled device has received the previous control signal, and the further signaling condition is satisfied A communication routine that only transmits a new control signal to the controlled device over a communication link.   The communication routine determines whether the difference between the control signal value generated for repeating the control routine and the value of the previous control signal transmitted to the controlled device is greater than a threshold value; 18. The process control system of claim 17, wherein it is determined whether the further signaling condition is satisfied.   The communication routine determines whether the further signaling condition is satisfied by determining whether the time since the previous control signal was transmitted to the controlled device has exceeded a maximum threshold time value. The process control system according to claim 17.   Whether the difference between the control signal value generated by the communication routine to repeat the control routine and the value of the previous control signal transmitted to the controlled device is greater than a threshold, or the previous 18. Determine whether the further signaling condition is satisfied by determining whether a time since a control signal was transmitted to the controlled device exceeded a maximum threshold time value. Process control system as described in.   21. A process control system according to any one of claims 17 to 20, wherein the communication routine is implemented by a computer processing device in the process controller.   The communication routine determines whether a difference between the control signal value for repeating the control routine and a value of the previous control signal transmitted to the controlled device is greater than a maximum change threshold; When the difference between the control signal value for routine iteration and the value of the previous control signal transmitted to the controlled device is greater than the maximum change threshold, a limited version for the control routine iteration The process control system according to any one of claims 17 to 21, wherein the new control signal is generated as the control signal value.   23. The process control system according to any one of claims 17 to 22, wherein a communication routine transmits the new control signal as a wireless communication signal to the controlled device.   24. A method as claimed in any one of claims 17 to 23, wherein the communication routine generates the new control signal to include a new control signal value and a time to implement the new control signal value at the controlled device. Process control system.   The process control system of claim 24, wherein the time to implement the new control signal value is an offset time.   25. The process control system of claim 24, wherein the time to implement the new control signal value is an absolute time.   When the control routine uses a feedback signal indicating an attribute of the controlled device to generate the control signal value, and the control routine generates the control signal for at least one control routine iteration; 27. A process control system according to any one of claims 24-26, wherein the controlled device is considered to have implemented the new control signal value at the predetermined time to determine the feedback signal.   28. A process control system according to any one of claims 17 to 27, wherein the control routine is a proportional, integral, derivative type control routine.   The control routine is a proportional, integral, derivative (PID) type control routine, and the process controller receives a feedback signal used as a feedback signal in the PID type control routine via a wireless communication link; The process control system according to any one of claims 17 to 28. A process control system for controlling a process,
A process controller including one or more processors, memory, and a communication interface;
A communication link;
A controlled device disposed within the process and communicatively coupled to the process controller via the communication link;
Stored in the memory, wherein the process controller executes on the one or more processors during each of a number of iterations to generate control signal values for use in controlling the controlled device. Control routines that are
(1) determining whether a predetermined minimum period has elapsed since the previous control signal was transmitted to the controlled device by the one or more processors;
(2) determining whether an acknowledgment is received from the controlled device indicating that the controlled device has received the previous control signal; and (3) whether further signaling conditions are met. An interface routine stored in the memory for performing the determining,
When the predetermined minimum period has elapsed since the interface routine (1) has transmitted a previous control signal to the controlled device, (2) the controlled device has received the previous control signal from the controlled device. The communication link based on the control signal value generated by the control routine during repetition when an acknowledgment is received indicating that a control signal has been received, and (3) when the further signaling condition is satisfied A new control signal is transmitted to the controlled device via (1) when the predetermined minimum period has not elapsed since the previous control signal was transmitted to the controlled device (2 ) When no acknowledgment is received from the controlled device indicating that the controlled device has received the previous control signal, or (3) the further When not meet the signaling conditions, on the basis of the control signal value which is generated by the control routine in a repeating, via the communication link, it does not transmit a new control signal to the controlled device, a process control system.   The further signaling when the difference between the control signal value generated by the interface routine to repeat the control routine and the value of the previous control signal transmitted to the controlled device is greater than a threshold value. The process control system according to claim 30, wherein the process control system determines that the condition is satisfied.   31. The interface routine determines that the additional signaling condition is satisfied if a time since the previous control signal was transmitted to the controlled device exceeds a maximum threshold time value. Process control system.   The difference between the control signal value generated by the interface routine to repeat the control routine and the value of the previous control signal transmitted to the controlled device is greater than a threshold value or the previous control 31. The process control system of claim 30, wherein the process control system determines that the additional signaling condition is met if any time since a signal was transmitted to the controlled device exceeded a maximum threshold time value. .   The interface routine further determines whether a difference between the control signal value for repeating the control routine and the value of the previous control signal transmitted to the controlled device is greater than a maximum change threshold; and When the difference between the control signal value for repeating the control routine and the value of the previous control signal transmitted to the controlled device is greater than the maximum change threshold, 34. A process control system according to any one of claims 30 to 33, wherein the new control signal is created as a limited version of the control signal value.   35. The process control system according to any one of claims 30 to 34, wherein the communication link is a wireless communication link.   35. The process control system according to any one of claims 30 to 34, wherein the communication link is a wired communication link.   37. A process control system according to any one of claims 30 to 36, wherein the interface routine creates a new control signal as a signal including a target value and a time to execute the target value on the controlled device.   38. The process control system of claim 37, wherein the time for implementing the target value is an offset time.   39. A process control system according to any one of claims 30 to 38, wherein the control routine is a proportional, integral, derivative (PID) type control routine.   40. A process control system according to any one of claims 30 to 39, wherein the control routine uses a feedback signal indicative of an attribute of the controlled device to generate the control signal value.   41. The process control system of claim 40, wherein the control routine uses a further feedback signal indicative of a measured process variable to generate the control signal value.   The interface routine creates a new control signal as a signal including a target value and a time to execute the target value on the controlled device, and the control routine generates the control signal value to generate the controlled signal value. Using a device attribute, the control routine assumes that the controlled device implements the target value at the time when the controlled device implements the target value to determine the attribute of the controlled device. Item 42. The process control system according to any one of Items 30 to 41.   And further comprising a sensor disposed within the process for measuring a process variable, and a further communication link disposed between the process controller and the sensor, wherein the control routine determines the control signal value. 43. A process control system according to any one of claims 30 to 42, wherein the process variable measured by the sensor is used for this purpose.   44. A process control system according to any one of claims 30 to 43, wherein both the communication link and the further communication link are wireless communication links.   44. The process control system according to any one of claims 30 to 43, wherein the communication link and the further communication link are both wired communication links.   44. The process control system according to any one of claims 30 to 43, wherein the communication link is a wired communication link and the further communication link is a wireless communication link.   44. A process control system according to any one of claims 30 to 43, wherein the communication link is a wireless communication link and the further communication link is a wired communication link. A process controller for use in controlling a controlled device in a process,
A processor;
Memory,
A process control routine stored in the memory that is executed by the processor during each of a number of iterations to generate a control signal value for controlling the controlled device in the process; A process control routine comprising a feedback type control routine, wherein the process control routine uses an attribute of the controlled device as a feedback variable to generate the control signal value;
A communication routine stored in the memory that is executed by the processor during one or more of the multiple iterations to transmit a new control signal to the controlled device based on the control signal value; A communication routine, wherein the new control signal includes a target value of the controlled device and a time to execute the target value;
The process control routine assumes that the controlled device has implemented the target value at the time of performing the target value during one or more of the multiple iterations, and as the feedback variable, A process controller that determines the attribute of the controlled device.   The process control routine implemented the target value at the time when the controlled device implements the target value before receiving an indication of the measured attribute value of the controlled device from the controlled device 49. The process controller of claim 48, wherein the process controller determines the attribute of the controlled device as the feedback variable.   50. A process controller according to any one of claims 48 to 49, wherein the process control routine comprises a proportional, integral, derivative type control routine.   51. A process controller according to any one of claims 48 to 50, wherein the process control routine uses the feedback variable to determine a reset contribution to the control signal value.   52. A process controller according to any one of claims 48 to 51, wherein the communication routine transmits the new control signal to the controlled device via a wireless communication link.   53. A process controller according to any one of claims 48 to 52, wherein the time for implementing the target value is an offset time.   53. A process controller according to any one of claims 48 to 52, wherein the time to implement the target value is an absolute time. A method for controlling a controlled device in a process using a control signal, comprising:
Performing the multiple iterations of a control routine at a process controller computing device to generate a control signal value for controlling the controlled device during each of multiple iterations, the control Implementing further comprising using an attribute of the controlled device as a feedback variable to generate the control signal value during each of the multiple iterations of a routine;
Generating one or more new control signals of the multiple iterations, wherein the new control signals include a target value of the controlled device and a time to execute the target value; ,
Transmitting the new control signal over a communication link to the controlled device;
During one or more of the multiple iterations of the control routine, the controlled device is considered to have implemented the target value at the time at which the target value is to be implemented, and as the feedback variable, the controlled variable Determining the attribute of the device.   Determining the attribute of the controlled device as the feedback variable, assuming that the controlled device implements the target value at the time when the controlled device implements the target value, the process controller computing device Performing the target value at the time when the controlled device implements the target value in at least one of the multiple iterations before receiving an indication of the measured attribute value of the controlled device from the controlled device 56. The method of claim 55, comprising determining the attribute of the controlled device as the feedback variable.   57. The method according to any one of claims 55 to 56, wherein performing the control routine comprises performing a proportional, integral, derivative type control routine.   58. A method according to any one of claims 55 to 57, further comprising using the feedback variable to determine a reset contribution to the control signal value.   59. A method according to any one of claims 55 to 58, wherein transmitting the new control signal over a communication link to the controlled device comprises transmitting the new control signal over a wireless communication link. .   60. A method according to any one of claims 55 to 59, wherein generating a new control signal comprises generating the time to implement the target value as an offset time.   60. A method according to any one of claims 55 to 59, wherein generating a new control signal comprises generating the time to implement the target value as an absolute time.