DE102016119421A1 - Speed-based control in a non-periodically updated controller - Google Patents

Abstract

One technique for controlling a process using slow or non-periodically received process variable measurements enables a more robust controller response to set point changes and disturbance changes even when the process variable feedback signals are at a rate on the order of the response time of the process dynamics or variable associated rate. The control technique implements iterations of a control routine to generate a control signal having a reset or rate contribution component that in one sense defines an expected process response to the control signal. If the controller does not have a new process variable reading available, then the reset or rate contribution component is held at zero or another previous level when the control signal is generated. However, the reset contribution component is iteratively recalculated each time a controller expires, even if no new process variable reading has been received, such that the output of the reset contribution component includes expected process changes that occur as a result of a setpoint or upshift change affecting the process input or output affects the control signal between times when actual process variable measurements are received at the controller. This technique renders the controller more robust in generating control signals in the presence of setpoint or upshift changes received between times when nonperiodic process variable measurements are received at the controller, and for better operation of the controller as the process variable feedback time interval increases , is the same or the same order of magnitude as the process response time.

Description

TECHNICAL PART

 The present patent relates to compensating for a method and system for providing speed-based control in a process control system that utilizes non-periodic control or slow feedback process variable communications, and more particularly, an apparatus and method configured for robustly controlling a process of implementing control. when receiving process variable feedback at a rate that is slow compared to process dynamics.

DESCRIPTION OF THE RELATED TECHNIQUE

 Process control systems such as distributed or scalable process control systems such as those used in chemical and mineral oil processing or other processes typically include one or more process controllers that communicate with each other, with at least one host or operator workstation and with one or more field devices via analog, digital or combined Analog / digital buses are paired. The field devices, which may be, for example, valves, valve actuators, switches and transmitters (e.g., temperature, pressure and flow rate sensors) perform functions such as opening or closing valves and measuring process parameters in the process. The process controller receives signals indicative of process measurements performed by the field devices and / or other information related to the field devices and uses this information to implement a control routine for generating control signals sent to the field devices via the buses to regulate the operation of the process. Information from the field devices and the controller are typically provided to one or more applications that are executed by the operator workstation to enable an operator to perform a desired function with respect to the process, such as viewing the current state of the process, modifying the process flow, etc.

Some process control systems, such as the DeltaV ^® system sold by Emerson Process Management, use function blocks or groups of function blocks called modules located in the controller or in different field devices to perform control and / or monitoring operations. In these cases, the controller or other device may have one or more functional blocks or modules each receiving inputs from and / or providing outputs to other functional blocks (either in the same device or in different devices), and a process operation such as measuring or Recognize a process parameter, monitor a device, or perform a control operation such as the implementation of a PID (Proportional-Differential-Integral) control routine. The different functional blocks and modules in a process control system are generally configured to communicate with each other (eg via a bus) to form one or more process control loops.

Process controllers are typically programmed to execute a different algorithm, subroutine, or control loop (which are all control routines) for each of a number of different loops defined for or included in such flow-rate loops, temperature control loops, pressure control loops, and so on , Generally speaking, each such control loop includes one or more input blocks, such as an analog input (AI) function block, a single output control block such as proportional-differential-integral (PID) or a fuzzy-logic-function block, and an output block such as Example an analog output (AO) function block. Control routines and the functional blocks that implement such routines have been configured according to a variety of control techniques, including PID control, fuzzy logic control, and model-based techniques such as a Smith Predictor or Model Predictive Control (MPC).

To support the execution of routines, a typical industrial or process plant has a centralized control room communicatively connected to one or more process controllers and process I / O subsystems, which in turn are connected to one or more field devices. Traditionally, analog field devices have been connected to the controller through two-wire or four-wire signal transmission and power current loops. An analog field device transmitting a signal to the control room (e.g., a sensor or transmitter) modulates the current flowing through the current loop so that the current is proportional to the sensed process variable. On the other hand, analog field devices that perform an action under the control of the control room are governed by the magnitude of the current through the loop.

As the amount of data transfer increases, a particularly important aspect of the process control system design includes the manner in which field devices are communicatively coupled to each other, to controllers and other systems or devices in a process control system or process plant. In general, the various communication channels, routes and paths that enable operation of the field devices within the process control system, collectively referred to collectively as the input / output (I / O) communication network.

The communication network topology and the physical connections or paths used to implement an I / O communication network can have a significant impact on the robustness or integrity of field device communications, especially when the network is exposed to adverse environmental factors or difficult conditions. These factors and conditions may include the integrity of communications between one or more field devices, controllers, and so on. The communications between the controllers and the field devices are particularly sensitive to such interruptions in that the monitoring applications or control routines typically require periodic updates of the process variables for each iteration of the routine. Therefore, compromised regular communications could result in reduced efficiency and / or profitability of the process control system as well as increased wear or damage to equipment as well as any number of potentially harmful failures.

In the interest of ensuring robust communications, I / O communication networks used in process control systems have traditionally been hardwired. Unfortunately, hardwired networks involve a number of complexities, challenges and limitations. For example, the quality of hardwired networks may decrease over time. Furthermore, hard-wired I / O communication networks are typically expensive to install, especially in cases where the I / O communications network is associated with a large industrial facility or facility that is distributed over a large area, for example, an oil refinery or a chemical Plant that extends over several 1000 m ^{2 of} land. The required long wiring paths typically involve significant amounts of labor, material, and cost, and can result in signal degradation due to wiring impedance and electromagnetic interference. For these and other reasons, hardwired I / O communication networks are generally difficult to reconfigure, modify, or update.

It has been proposed to use wireless I / O communication networks to alleviate some of the difficulties associated with hardwired I / O networks. For example, US Patent Application Publication No. 2003/0043052 entitled "Apparatus for Providing Redundant Wireless Access to Field Devices in a Distributed Control System," the entire disclosure of which is expressly incorporated herein by reference, discloses a system using wireless communications to enhance or supplement the use of hardwired communications.

The reliance on wireless communications for rule-based transmissions has traditionally been limited, among other things, due to reliability concerns. As described above, modern monitoring applications and process control rely on reliable data communication between the controller and the field devices to achieve optimal control levels. Furthermore, typical controllers perform control algorithms at high speeds to quickly correct unwanted deviations in the process. Undesirable environmental factors or other adverse conditions may create intermittent disturbances that may hinder or prevent the rapid communications needed to support such execution of monitoring and control algorithms. Fortunately, wireless networks have become much more robust over the last two decades, so that wireless communications can be reliably used in some types of process control systems.

However, power consumption continues to be a complicating factor in the use of wireless communications in process control applications. Because wireless field devices are physically isolated from the I / O network, the field devices typically must have their own power source. Accordingly, field devices may be battery powered, draw solar power, or branch ambient energy such as vibration, heat, pressure, and so on. For these devices, the energy consumed for data transmission can make up a significant proportion of the total energy consumption. In fact, during the process of establishing and maintaining a wireless communication link, more power may be consumed than in other important operations performed by the field device, such as the steps performed to acquire or recognize the measured process variables. To reduce power consumption in wireless process control systems, and thus to extend battery life, it has been proposed to implement a wireless control system in which the field devices, such as sensors, communicate with the controller in a non-periodic, slow or intermittent manner. In one case, the field devices may only communicate with the controller or send process variable measurements to it when a significant change in a process variable has been detected that results in non-periodic communications with the controller.

A control technique developed for handling non-periodic process variable measured value updates utilizes a control system that provides and maintains an indication of an expected process response to the control signal generated by the controller between the rare or non-periodic measured value updates. An expected process response can be developed with a mathematical model that calculates an expected process response to a control signal for a given measurement update. An example of this technique is in U.S. Patent No. 7,587,252 entitled "Non-Periodic Control Communications in Wireless and Other Process Control Systems", the disclosure of which is expressly incorporated herein by reference. In particular, this patent discloses a control system with a filter which generates an indication of an expected process response to a control signal upon receipt of a non-periodic process variable measurement value update and results in the generated expected process response indication until the arrival of the next non-periodic process variable measurement value update. As another example, that U.S. Patent No. 7,620,460 entitled "Process Control With Unreliable Communications," the entire disclosure of which is expressly incorporated herein by reference, discloses a system that includes a filter that provides an indication of an expected response to the control signal but further modifies the filter to provide a measurement the time that has elapsed since a last non-periodic measurement update to produce a more accurate indication of the expected process response.

However, in many control applications, a process control system may receive a setpoint change during a process operation. In general, when a setpoint is changed when operating a periodically updated control system (eg, a hardwired control communication system), a controller configured to perform a proportional action on the fault between the setpoint and the measured process variable immediately changes the controller output drive the process variable towards the new steady-state value. However, in a wireless control system that receives infrequent, non-periodic measurement updates that operates as described in the two examples above, the measured process response reflected by each new measurement update reflects changes made to the controller output that was made based on the last measurement update; in addition to changes in the output resulting from the setpoint change that was made sometime after receiving the last measured value update. In this case, the calculation of the controller reset component may be based on the controller output and the time since the last measurement update (as in U.S. Patent No. 7,620,460 described above) overcompensate the changes made after the last measurement update. The process response to a setpoint change may therefore differ depending on when the setpoint change was made after the last measured value update. Consequently, this system does not respond so quickly and robustly to a setpoint change as the controller continues to rely on a previously generated (and now outdated) indication of the expected response in the development of the control signal after a setpoint change. To overcome this problem, US Patent Application Publication No. 2013/0184837, entitled "Compensating for Setpoint Changes in a Non-Periodically Updated Controller," the entire disclosure of which is expressly incorporated herein by reference, discloses a system that uses a continuous flow system updated filter is used in a feedback loop in the controller to keep track of the controlled variable's operation during times when no new process variable reading is received, and uses that controller's output when a new process variable reading is received at the controller, but otherwise, it uses the output of the filter from the most recent time a measurement value of the process variable was received to generate a control signal. In this system, the generated control signal responds better and works better when there are changes in the setpoint of the process variable split times in which process variable measurements are received.

In addition, when using battery powered transmitters in wireless control systems, it is desirable to set up the system to maintain a long battery life. For example, to achieve battery life of 3-5 years, with current transmitter and battery technology, it is generally necessary to use a communication update rate of 8 seconds or more. However, using such a slow refresh rate limits the application of PID (Proportional-Integral-Derivative) -based wireless control to processes that have a process response time of 30 seconds or more because it is important to continue to have process feedback measurements is received at a rate at least four times the rate associated with the response time of the process (ie, reversing the process response time) to maintain control of the process.

In addition, there are various types of PID algorithms that can be used to address wireless control, including those that produce a position output, eg, a 4-20 ma signal or digital signal, to the valve or other controlled element is created to tell the element the final position to move to. However, other PID algorithms exist that provide speed-based control signals that instruct the valve or other controlled element to move a certain amount in a particular direction, for example, by exciting the movable element for a certain period of time. Such velocity-based control signals are commonly used with electric motors and generate control signals in the form of pulsed signals (having a pulse width that is modulated to indicate the amount of time the valve must be energized for the movable element to move for a certain period of time). Speed-based controllers tend to produce a change in the position signal relative to a signal indicating an actual position to be occupied by the movable element. Thus, rate-based control algorithms are often used to apply an incremental (increase / decrease) output to an actuator, and thus may be used in controlling actuators that may not provide position feedback.

SUMMARY

 A control technique allows the robust control of a fast dynamics process or loop with respect to the rate at which measured values of a controlled process variable are provided to the process controller as feedback. In particular, the control technique uses a position or velocity form of a PID algorithm to control processes in which the controller is provided with process variable measurements or feedback signals in a time interval equal to or even greater than the process response time. In particular, the control technique may be used to provide robust control in processes having a response time that is two to four times less than the feedback time interval. Such situations may arise, for example, when wireless control is used in which the process variable feedback measurements are provided to the controller wirelessly, intermittently, or at a time interval that is less than or even greater than the response time of the process.

The disclosed speed PID control routine may be used in many different situations, such as to perform control with wireless measurement when the actuator requires incremental input and no position feedback is available to the controller to perform closed loop control if there is an interface to an actuator that requires position or incremental input, and to address traditional installations as well as newer installations that use wireless measurements in the control. In addition, tuning the speed of the PID algorithm can be done based on process gain and dynamics, and is independent of the wireless communication rate. In addition, the PID control routine's speed mode automatically maintains the last delivery position in the event of a loss of communication and allows bumpless recovery when the communications are restored.

In one case, the controller implementing the new control technology includes a different structure in that different proportional, integral, and derivative control signal components are generated and used to generate a differential or motion based control signal, which is then sent to the regulated device, such as the Example, a valve is sent to regulate the operation of the controlled device and thus the process. This differential or velocity based control generates a control signal that works better than standard PID control in the presence of slow process variable feedback measurements. In particular, at each controller iteration, the controller applying this control technique generates a differential proportional value representing the difference between a previous proportional control signal component and a recalculated proportional control signal component, and this differential proportional value is used as the basis for each new control signal from the controller , However, various other control signal components, for example, a differential and / or an integral control signal component may also be added or combined with the differential proportional control signal component when a new process variable measured value signal is available at the controller. These two control signal components can also be based on differentials between recalculated values and previously calculated values. In particular, a new differential component may be calculated during the controller iterations in which a newly received value of a process variable measurement is available at the controller. Also, a new integral component may be developed with a continuously updated filter that generates a new indication of an expected response of the process for each controller routine iteration of the controller. However, the output of the continuously updated filter is used to generate a new integral component only when a new value of process variable measurement is received. At other times, the integral control signal component is set to zero.

The velocity-based PID control technique disclosed herein uses the differential waveform to generate a control signal that rapidly adapts to changes in the set point (even between times when a process variable feedback signal is applied to the input of the controller) while still providing robust and stable control in the presence of slowly received (eg intermittent) feedback signals, including feedback signals received at a rate smaller (eg, even two to four times smaller than) close to or greater than the inverse of the response time of the regulated process.

BRIEF DESCRIPTION OF THE DRAWINGS

1 FIG. 10 is a block diagram of an exemplary periodically updated hardwired process control system.

2 FIG. 10 is a graph illustrating a process output response to a process input for an exemplary periodically updated hardwired process control system including the process response time. FIG.

3 Figure 10 is a block diagram illustrating an example of a wireless process control system with a controller receiving slow or non-periodic feedback inputs.

4A FIG. 10 is a block diagram of an example controller that provides robust compensation for setpoint changes or disturbance inputs in a non-periodically updated wireless process control system.

4B is a graph showing the process output response of an example controller of 4A illustrated while the controller responds to multiple setpoint changes.

5 FIG. 10 is a block diagram of an example controller that performs setpoint change compensation in a non-periodically updated process control system in which the controller compensates for a process and / or measurement delay in the feedback signal.

6 10 is a block diagram of an example controller that performs setpoint change compensation in a non-periodically updated process control system in which the process controller uses a differential, or rate, contribution to determining a control signal.

7 FIG. 10 is a block diagram of an example controller that performs setpoint change compensation in a non-periodically updated process control system in which the process controller receives additional controller input data provided by a field device, controller, or other downstream device to provide a response in the process flow to influence.

8th FIG. 10 is a block diagram of an example controller that performs setpoint change compensation in a non-periodically updated process control system in which the process controller receives the use of actual or implied controller input data for a field device.

9 FIG. 10 is a block diagram of an exemplary rate-based PI controller that allows for robust compensation of setpoint changes or disturbance inputs in a process control system in response to slowly received process variable measured value signals.

10 FIG. 10 is a block diagram of an exemplary rate-based PID controller that allows for robust compensation of setpoint changes or disturbance loading in a process control system in response to slowly received process variable measured value signals.

11A FIG. 10 is a graph illustrating the simulated process response of an exemplary prior art velocity-based PID controller in both a wired and a wireless configuration in response to a setpoint change in the primary control variable and with a process response time of 8 seconds. FIG.

11B FIG. 10 is a graph illustrating the simulated process response of an exemplary rate-based PID controller according to the present invention in both a wired and a wireless configuration in response to a setpoint change in the primary control variable and with a process response time of 8 seconds. FIG.

12A FIG. 10 is a graph depicting the simulated process response of an exemplary prior art velocity-based PID controller in both a wired and a wireless configuration in response to a setpoint change in the primary control variable. FIG and illustrated with a process response time of 3 seconds.

12B FIG. 10 is a graph illustrating the simulated process response of an exemplary rate-based PID controller according to the present invention in both a wired and wireless configuration in response to a setpoint change in the primary control variable and a 3 second process response time. FIG.

13A FIG. 10 is a graph illustrating the simulated process response of an exemplary rate-based PID controller in both a wired and wireless configuration in response to a fault change and with a process response time of 8 seconds. FIG.

13B FIG. 10 is a graph illustrating the simulated process response of an exemplary rate-based PID controller according to the present invention in both a wired and wireless configuration in response to a change in interference and with a process response time of 8 seconds. FIG.

14A FIG. 10 is a graph illustrating the simulated process response of an exemplary prior art velocity-based PID controller in both a wired and wireless configuration in response to a disturbance change and with a 3 second process response time. FIG.

14B FIG. 10 is a graph illustrating the simulated process response of an exemplary rate-based PID controller according to the present invention in both a wired and wireless configuration in response to a disturbance change and with a 3 second process response time.

DETAILED DESCRIPTION

 A control technique may be used to perform closed loop control in a process loop in which process measurement feedback signals are received slowly or intermittently, and is particularly useful when receiving the process measurement feedback signals at a rate lower than, or similar how or only slightly higher than the rate at which the process dynamics are controlled, such as reversing the process response time. This controller may be used, for example, in controllers that receive process measurement signals as feedback signals in a slow and / or non-periodic manner, and more particularly at a rate that is lower or the same magnitude or otherwise similar to the process response rate of the controlled process dynamics (ie, reverse the process response time for the controlled process variable). In one case, the control technique generates a control signal for use in controlling a process device, such as a valve, by combining a proportional contribution signal with one or more of a differential contribution signal and an integral contribution signal. In a case where a rate-based PID algorithm is used, the controller generates a proportional contribution value from a difference between a setpoint and a last received process variable feedback feedback signal. This error signal is then multiplied by a gain signal and applied to a difference unit which determines the change in that signal since the last execution cycle of the controller. Further, a differential unit may receive the error signal and performs a differential calculation on the error signal substantially involving a differential of the error signal over time since the receipt of the last measurement value signal at the controller. The output of the differential module or calculation is also provided to a change detection unit or a difference unit which determines the difference between the current output of the differential calculation and the previous value used in the calculation of a control signal. Likewise, an integral calculation unit receives and integrates (e.g., sums) the difference of the control signal as generated by the proportional and differential units. The output of the summer is applied to a filter which filters the summer output to produce an integral contribution signal. However, this integral contribution is applied to a summer, which sums this contribution to the output of the control signal only when a new feedback value is provided to the controller, i. the integral contribution is set to zero for all controller iterations except those where the controller has a new feedback signal.

Generally speaking, the continuously updated integral contribution filter in the controller generates an expected process response indication (also referred to as feedback contribution) at each controller routine iteration, despite the slow or non-periodic receipt of process variable measurement value updates from field devices. The continuously updated filter partially utilizes a previously generated indication of an expected response from the last routine iteration and the policy routine expiration period to generate the indication of an expected response at each routine iteration. In addition, an integral output switch in the controller provides an output of the continuously updated filter as a feedback contribution, such as an integral (also called Reset) contribution based on the most recent readings to the control signal. Generally speaking, the integral output switch produces an expected process response as from the continuously updated filter at the time the last measurement update was received from the controller, or a zero value in a velocity form of the PID controller as the integral or Reset contribution to the control signal at each iteration of the controller ready, in which no new measured value signal is available. When a new measurement update is available, the integral output switch snaps to a new indication of the expected process response generated by the continuously updated filter (based on an indication of the new measurement update) and provides the new expected process response as the integral contribution of the control signal. Thus, using the continuously updated filter, the controller determines a new expected response of the process at each controller iteration, with each new expected process response reflecting the impact of a set point change or upshift that occurred between measured value updates and the controller output during development of the control signal, although the integral or reset component of the control signal is changed only when a new measured value is available at the controller.

1 illustrates a process control system 10 that can be used to implement the described policy methodologies. The process control system 10 includes a process controller 11 that with a data history 12 and with one or more host workstations or computers 13 (which may be PCs, workstations, etc.) of any type, each with a display screen 14 connected is. The controller 11 is also with field devices 15 - 22 via input / output (I / O) cards 26 and 28 connected. The data history 12 may be any desired type of data collection unit having any desired storage type and any desired or known software, hardware or firmware for storing data. The controller 11 is in 1 communicative with the field devices 15 - 22 connected via a hardwired communication network and communication scheme.

In general, the field devices 15 - 22 any type of device such as sensors, valves, transmitters, positioning, etc., while the I / O cards 26 and 28 can be any type of I / O device that conforms to any desired communication or controller protocol. The controller 11 includes a processor 23 , one or more in a store 24 stored or stored process control routines (or any module, block or subroutine thereof). Generally speaking, the controller 11 communicates with the devices 15 - 22 , the host computers 13 and the data history 12 to control a process in any desired manner. In addition, the controller implements 11 a control strategy or scheme by what is commonly referred to as functional blocks, where each functional block is an object or other part (eg, a subroutine) of an overall control routine that works in conjunction with other functional blocks (links referred to) to process loops within of the process control system 10 to implement. Function blocks typically carry out a control function associated with an input function such as that associated with a transmitter, sensor, or other process parameter measuring device, such as the control routine associated with a control routine that performs PID, fuzzy logic, etc., or an output function of a device such as a valve to perform a physical function within the process control system 10 perform. Of course, there are also hybrid and other types of functional blocks that can be used herein. The function blocks can be in the controller 11 or stored in other devices as described below.

As by the exploded block 30 from 1 Illustrated, the controller can 11 include a series of single loop control routines, such as a control routine 32 and 34 and, if desired, may implement one or more advanced closed loop loops, such as a closed loop 36 illustrated. Each such control loop is typically referred to as a control module. The figure illustrates the single loop control routines 32 and 34 as a single loop control with a single input / single output fuzzy logic control block or a single input / single output PID control block, connected to appropriate analog input (AI) and analogue output (AO) function blocks connected to process control devices such as valves, with gauges such as temperature and pressure transmitters or with any other device in the process control system 10 can be associated. The advanced control loop 36 is with an evolved rule block 38 illustrated with inputs that are communicatively connected to one or more AI function blocks, and outputs that are communicatively connected to one or more AO function blocks, although the inputs and outputs of the evolved rule block 38 may also be connected to any other desired function blocks or control elements to receive other types of inputs and provide other types of control outputs. The evolved rule block 38 may implement any type of multi-input, multi-output control scheme, and may form a model predictive control (MPC) block, a neural network modeling or control block, a multivariable fuzzy logic rule block, a real time optimization block, etc., or include. It will be understood that the in 1 illustrated functional blocks containing the evolved control block 38 include, with the standalone controller 11 or alternatively be located in and executed by any other processing device or control element of the process control system, such as one of the workstations 13 or one of the field devices 19 - 22 , For example, the field devices 21 and 22 , which may each be a transmitter and a valve, may execute control elements to implement a control routine, and thus include processing and other components for processing parts of the control routine, such as one or more functional blocks. More specifically, the field device 21 can a memory 39A to store logic and data in conjunction with an analog input block while the field device 22 an actuator with a memory 39B for storing logic and data associated with a PID or other control block in combination with an analog output (AO) block, as in 1 illustrated.

The curve of 2 generally illustrates a process output responsive to a process input for a process control system based on the implementation of one or more of the control loops 32 . 34 or 36 (and / or any control loop, that in the field devices 21 and 22 or other devices containing functional blocks) has been developed. The implemented control routine generally runs in a periodic fashion over a series of controller iterations, the times of the control routine flow in 2 along the timeline through the thick arrows 40 be indicated. In a conventional case, each rule routine iteration 40 by an updated process measurement value provided, for example, by a transmitter or other field device, indicated by the thin arrows 42 is hinted at. As in 2 Typically, multiple periodic process measurements are shown 42 and by the control routine between each of the periodic control routine expiration times 40 receive. To avoid the limitations associated with synchronizing the measured value with the control flow, many known process control systems (or control loops) are designed to oversample the process variable measurement by a factor of 2-10. Such oversampling helps to ensure that the process variable metric is up-to-date for use in the control scheme at each rule routine expiration or interaction. Similarly, to minimize rule variation, conventional designs dictate that feedback-based control should be performed 4-10 times faster than the process response time and that a new process variable reading be available at each controller iteration. The process response time is in a process response time curve 43 the curve of 2 is represented as the time spent with a process time constant (τ) (eg 63% of the process variable change) plus a process delay or dead time (T _D ) after an implementation of a step change 44 in a process input (in the lower line 45 from 2 shown). In any event, to meet these conventional design requirements, the process measurement updates (indicated by arrows 42 from 2 indicated) and provided to the controller at a much higher rate than the control routine drain rate (indicated by the arrows 40 from 2 displayed), which in turn is much faster or higher than the process response time.

However, obtaining frequent and periodic samples from the process may not be practical or even possible when a controller is operating in a process control environment in which, for example, the controller receives readings wirelessly from one or more field devices. In particular, in these cases, the controller may only be able to receive slow process variable measurements (to conserve battery life of the wireless sensors / transmitter) or non-periodic process variable measurements. In addition, in these cases, the time between non-periodic or even periodic process variable measurements may be longer than the control routine drain rate (indicated by the arrows 40 from 2 indicated). 3 shows an exemplary wireless process control system 10 which involves the application of slow and / or non-periodic wireless communications of process control data or process variable measurements to a controller 11 can implement.

The control system 10 from 3 is by its nature the regulatory system 10 from 1 similar, with like elements numbered the same. The control system 10 from 3 includes a number of field devices 60 - 64 and 71 that communicates wirelessly with the controller 11 and potentially coupled with each other. As in 3 Illustrated is the wirelessly connected field device 60 with an antenna 65 connected and cooperates for wireless communication with an antenna 74 , in turn, with a wireless I / O device 68 is coupled. Furthermore, the field devices 61 - 64 with a wired-to-wireless conversion unit 66 connected, in turn, with an antenna 67 connected is. The field devices 61 - 64 communicate wirelessly through the antenna 67 with an antenna 73 that with another wireless I / O device 70 connected is. Like also in 3 is shown, includes the field device 71 an antenna 72 connected to one or both of the antennas 73 and 74 communicates with the I / O devices 68 and or 70 to communicate. The I / O devices 68 and 70 are in turn communicative with the controller 11 via a wired backplane connection (in 3 not shown). In this case, the remain field devices 15 - 22 with the controller 11 via the I / O devices 26 and 28 hardwired.

The process control system 10 from 3 generally uses the wireless transmission of measured, acquired or calculated data by the transmitters 60 - 64 or other rule elements, such as the field device 71 , as described below. In the control system 10 from 3 It is assumed that new process variable readings or other signal values through the devices 60 - 64 and 71 on a slow or non-periodic basis to the controller 11 be sent, such as when certain conditions are met. For example, a new process variable reading may become the controller 11 are sent when the process variable value changes by a predetermined amount with respect to the last process variable reading from the device to the controller 11 was sent. These signals may also be sent periodically, but at a much lower rate than normal process control systems such as wired process control signals. For example, the slow periodic feedback rate may be less than the controller processing rate (the rate at which the controller generates new control signals for use in generating a control signal), and may be a rate using the control techniques described herein is less than or equal to or similar to the process response rate or response time, such as a rate that is less than 2-4 times the response rate of the controlled process dynamics. Here, the process response rate is the reversal of the process response time. Of course, in addition or instead, other ways of determining when process variable measurements should be sent in a periodic or non-periodic manner may be implemented.

It will be understood that each of the transmitters 60 - 64 from 3 a signal indicating a respective process variable (eg, a flow, pressure, temperature, or level signal) to the controller 11 for use in one or more control loops or routines or for use in a monitoring routine. Other wireless devices, such as the field device 71 , Process control signals may be received wirelessly and / or may be configured to send other signals indicating a different process parameter. Generally speaking, as in 3 shown, the controller includes 11 a communication stack 80 running on a processor to process the incoming signals, a module or a routine 82 running on a processor to detect when an incoming signal includes a measurement update and one or more control modules 84 running on a processor to perform control based on the measurement update. The detection routine 82 may generate a flag or other signal to indicate that data is being transmitted through the communication stack 80 provided include a new process variable metric or other type of update. The new data and the new update flag may then be one or more of the rule modules 84 (which may be functional blocks), which are then provided by the controller 11 are processed at a predetermined periodic drain rate, as will be described in more detail below. Alternatively or additionally, the new data and update flags may be provided to one or more monitoring modules or applications included in the controller 11 or elsewhere in the rule system 10 to run.

The wireless (or other) transmitters of 3 generally lead to slow or non-periodic transmission involving irregular or otherwise less frequent data transfers between the field devices 60 - 64 and 71 and the controller 11 , However, as noted above, the transmission of readings from the field devices was 15 - 22 to the controller 11 conventionally structured so as to be performed in a periodic manner at a rate far greater than the controller's drain rate, or much higher than the dynamic rate of the process, ie reversing the process response time (for the controlled process phenomena). Consequently, the control routines are in the controller 11 generally for periodic updates in the feedback loops of the controller 11 used process variable measured values designed.

To record the slow, non-periodic, or otherwise unavailable metric updates (and other unavailable communications broadcasts), such as through the wireless communications between some of the field devices and the controller 11 can be introduced, the control and monitoring routine (s) of the controller 11 restructured or modified as described below to allow the process control system 10 Works correctly when slow, including non-periodic or non-periodic or intermittent updates are used, and especially when these updates occur less frequently than the controller's execution rate 11 and even if these updates are received at a rate that is similar (eg, less than 2-4 times or the same order of magnitude, etc.) as the process response rate (eg, reversing the process response time of the controlled process variable). Exemplary control schemes configured to work with slow and / or non-periodic, rule-based communications are described in more detail in FIG 4 - 10 illustrated. For example, 4A schematically illustrates a position type of process controller 100 that with a process 101 is coupled. That of the controller 100 (the controller 11 of the 1 and 3 or a control element of a field device, eg one of the wireless field devices of 3 The control scheme implemented in general includes the functionality of the communication stack 80 , the update detection module 82 and one or more of the rule modules 84 that in conjunction with 3 are illustrated and described, and generates a control signal indicating the position in which a movable element of a control device is to move.

In the exemplary system of 4A the controller receives 101 a setpoint signal from, for example, one of the workstations 13 ( 1 and 3 ) or from another source in or in communication with the process control system 10 , and generates one or more control signals 105 that the process 101 from an output of the controller 100 to be provided. In addition to the receipt of the control signal 105 can the process 101 subject to measured or unmeasured disturbances, indicated schematically by the arrow 104 are indicated. Depending on the type of process control application, the setpoint signal may occur at any time during the regulation of the process 101 for example, by a user, a setting routine, etc. are changed. The process control signals 105 may, of course, control an actuator associated with a valve or may control any other field device to provide an answer in the operation of the process 101 to influence. The answer of the process 101 to changes in the process control signals 105 is from a transmitter, sensor or other field device 106 measured or recorded, for example, one of the in 3 illustrated transmitter 60 - 64 can correspond. The communication link between the transmitter 106 and the controller 100 can include a wireless connection and is in 4A illustrated with a dashed line.

In a simple embodiment, the controller 100 implement a closed loop single input / single output control routine, such as a PI control routine, which is in the form of a PID control routine. Accordingly, the controller includes 100 multiple standard PI rules, including a communication stack 80 , and a control signal generation unit with a summation block 108 , a proportional gain element 110 , another summation block 112 and a high-low limiter 114 , the control routine 100 also includes a direct feedback path with a filter 116 and an integral output switch comprising a selection block 118 includes. The filter 116 is with the output of the high-low limiter 114 coupled and the block 118 of the switch is connected to the output of the filter 116 coupled and provides the summation block 112 the integral or reset contribution or component of the control signal provided by the controller 100 is generated, ready.

During operation of the controller 100 compares the summation block 108 the setpoint signal with the last received process variable reading from the communication stack 80 in the controller 100 has been provided to generate an error signal. The proportional gain element 110 acts on the error signal, for example, by multiplying the error signal by a proportional gain K _p to produce a proportional contribution or component of the control signal. The summation block 112 then combines the outcome of the winning element 110 (ie the proportional contribution) to the integral or reset contribution or component of the control signal generated by the feedback path to produce a control signal that is not limited in nature. The delimiter block 114 then performs a high-low limit on the output of the summer 112 through to the process of regulating 101 to be sent control signal 105 to create.

Significantly, generate the filter 116 and the block or switch 118 in the feedback path of the controller 100 the integral or reset contribution component of the control signal in the following manner. The filter 116 which is to receive the output of the limiter 114 coupled, generates an indication of the expected process response to the control signal 105 based on the output value of the limiter 114 and the expiration period or time of the control algorithm 100 , The filter 116 places this Expected Process Response signal to the switch or block 118 at. The switch or block 118 samples the output of the filter 116 at the output of the switch or block 118 and locks it whenever a new process variable reading is received, and holds that value until the next process variable output on the communications stack 80 Will be received. This leaves the output of the switch 118 the output of the filter 116 which was sampled at the last measurement update.

The expected process response to changes in the output of the summer 108 through the filter 116 can be approximated with a first order model, as described in more detail below. More generally, however, the expected process response may be with any suitable model of the process 101 be generated and is not on a in a feedback path of the controller 100 limited model or to a filter or a model associated with the determination of an integral or reset contribution to a control signal. For example, controllers that provide a model for providing the expected process response can use a differential contribution, so that the control routine 101 PID control scheme implemented. Several examples, including exemplary types of differential contributions, will be described below in connection with FIGS 6 - 8th described.

wobei

K_p

= Proportionalgewin

T_Reset

= Reset, Sekunden

O(s)

= Regelausgang

E(S)

= Regelfehler

Before detailed discussion of the operation of the filter 116 from 4 It is useful to note that a conventional PI controller can be implemented with a positive feedback network to determine the integral or reset contribution. Mathematically, it can be shown that the transfer function for a conventional PI implementation is equivalent to the standard open-loop formulation, ie, where the output is not limited. In particular:

in which

K _p

= Proportional thread

T _reset

= Reset, seconds

O (s)

= Control output

IT)

= Control error

An advantage of using the positive feedback path in the controller 100 as in 4A illustrated that a wind-up of the reset contribution is automatically prevented when the controller output is high or low limited, ie by the limiter 114 ,

In any case, the control technique described below allows the use of the positive feedback path to determine the reset or integral contribution when the controller receives non-periodic updates of the process variables while still allowing a robust controller response in the event of setpoint changes or switching changes occurring between receive new process variable metrics. Specifically, to provide robust setpoint change controller operation, the filter is 116 to calculate a new indication or value of an expected process response each time the controller expires 100 regardless of whether this output of the filter is ever sent to the summation block 112 is created. Consequently, the output of the filter becomes 116 at each expiration cycle, the controller routine regenerates, although only the one immediately after the controller 100 generated output of the filter 116 a new process value update from the communication stack 80 is received as an integral or reset contribution in the summer 112 uses [sic].

wobei

F_N

= Neuer Filterausgang

F_N-1

= Filterausgang lettzer Ablauf

O_N-1

= Controller Ausgang letzter Ablauf

ΔT

= Controller Ablaufperiode

In particular, the new ad will show the expected response as from the filter 116 generated at each controller execution cycle calculated by the current controller output (ie the control signal after the limiter 114 ), displaying an expected response from the filter 116 generated during the last (ie immediately preceding) controller expiration cycle, and the controller expiration period. Consequently, the filter becomes 116 herein described as continuously updated because it is executed to generate a new process response estimate at each controller expiration cycle. The following is an example equation, that of the continuously updated filter 116 can be implemented to generate a new expected process response or filter at each controller expiration cycle:

in which

F _N

= New filter output

F _N-1

= Filter output lettzer drain

O _N-1

= Controller output last process

.DELTA.T

= Controller expiration period

It is noted here that the new filter output F _{N-1 is} iteratively determined as the most recent filter output F _N-1 (ie the current filter output value) plus a decay component, determined as the difference between the current controller output value O _N-1 and the current filter output value F _N-1 multiplied by a factor as a function of the reset time T _Reset and the controller expiration period ΔT. Due to the use of a filter that continuously updates in this way, the control routine can 100 better determine the expected process response in calculating the integral control signal input when a new process variable reading is received, and thereby better respond to changes in the setpoint or other disturbance upsets that occur between receipt of two process variable measurements. More specifically, it will be noted that changing the setpoint (without receiving a new process measurement) will immediately result in a change in the error signal at the output of the summer 108 leads, which changes the proportional contribution component of the control signal and thus the control signal. Consequently, the filter starts 116 immediately with the generation of a new expected response of the process to the changed control signal and thus updates its output before the controller 100 receives a new process reading. If then the controller 100 receives a new process reading and a sample of the filter output to the input of the summer 112 from the counter 118 is locked, as Integral or reset contribution component of the control signal should be used, then the filter has 116 iterates on an expected process response, to some extent at least to the response of the process 100 responded to the change in the setpoint or integrated it.

Calculated in the past, for example in the systems included in the U.S. Patent Nos. 7,587,252 and 7,620,460 described in the feedback path of a non-periodically updated controller reset contribution filter only a new display of an expected response when a new process variable reading was available. Thus, the reset contribution filter did not compensate for set point changes or disturbance upsets that occurred between receipt of process variable measurements because the setpoint changes or disturbance upsets of measured value updates were completely independent. For example, if a setpoint change or feedforward occurred between two measurement updates, then the expected process response of the controller was likely to be skewed because the calculation of the new display was the expected response to the time since the last measurement update and the current controller output 105 based. Consequently, the filter could 116 do not begin to consider the timing changes in the process (or control signal) resulting from a set point change (or other feedforward) occurring between the receipt of two process variable measurements on the controller.

One will understand, however, that the control routine 100 from 4A provides an expected process response by basing its calculations on nonperiodic readings, and additionally determining the expected response between the receipt of two readings to account for changes made by a change in the setpoint (or a measured disturbance introduced as a strobe input to the controller 100 used). Thus, the control technique described above can accommodate setpoint changes, load action mappings, etc. that may affect the expected process response, thus providing a more robust control response.

It will be understood that the in 4A illustrated control technique an indication of an expected response via the continuously updated filter 116 (eg the reset contribution filter) for each expiration of the rule block or routine 100 calculated. Here the controller configures 100 the continuously updated filter 116 to calculate a new indication of expected response for each run of the rule block. However, to determine if the output of the filter 116 as input to the summation block 112 to use, process the communication stack 80 and, in some examples, the update detection module 82 ( 3 ) the incoming data from the sender 106 to a new value flag for the integral output switch 118 when a new process variable reading is received. This new value flag informs the switch 118 to sample and snap the filter output value for this controller iteration to the input of the summer 112 ,

Regardless of whether a new value flag is transmitted, the continuously updated filter sets 116 the calculation of an expected response indication for each iteration of the control routine. This new indication of an expected answer will be to the integral output switch 118 supplied with each execution of the control block. Depending on the presence of the new value flag, the integral output switch switches 118 between allowing the new display of the expected response from the continuously updated filter 116 for passing to the summation block 112 and holding the signal previous to the summing block 112 was supplied at the last expiration of the control block. More specifically, when a new value flag is transmitted, then the integral output switch fails 118 the last computed display of the expected response from the continuously updated filter 116 to the summation block 112 to. Conversely, if the new value flag is not present then the integral output switch will send 118 the display of the expected response from the last rule block iteration to the summation block 112 New. In other words, the integral output switch 118 snaps to the new display of expected response every time a new value flag is popped off 80 is transmitted, but leaves no newly calculated display of the expected response the summation block 112 reach if there is no new value flag.

This control technology allows it to be that continuously updated filter 116 the expected process response continues to be modeled regardless of whether a new measurement is being transmitted. If the control input changes as a result of a set point change or an upshift action based on a measured disturbance, regardless of the presence of a new value flag, then the continuously updated filter reflects 116 correctly, the expected process response by calculating a new indication of an expected response at each control routine iteration. The new indication of the expected response (ie the reset contribution or integration component) will only be included in the controller calculations when a new value flag is transmitted (via the integral output switch) 118 ) becomes.

An in 4B illustrated curve 200 illustrates a simulated operation of the controller 100 from 4A when driving a process output signal 202 to a steady-state value, while the controller 100 responds to several setpoint changes. 4B shows a process output 202 (illustrated as a bold line) against a setpoint signal 204 (illustrated as a thinner line) in a wireless operation in a process control system. When a set point change occurs, as indicated by the arrows along the time axis at the bottom of the curve 200 displayed, then the controller responds 102 by producing a control signal that drives the process output to respond to the new setpoint (ie, the steady state value). For example, as in 4B illustrated, a setpoint change occurs at time T ₁ , as based on the setpoint signal 204 recognizable that changes its size significantly from a higher value to a lower value. In response, the controller is driving 102 the process variable associated with the setpoint to the new steady state or setpoint in a smooth transient curve, as based on the output signal 202 between the times T ₁ and T _{2 is} apparent. Likewise occurs in 4B a second setpoint change at time T ₂ , as based on the size of the setpoint signal 204 which changes significantly from a lower value to a higher value. In response, the controller regulates 102 the process variable associated with the setpoint change to the new steady state or set point in a smooth transient curve, as based on the output signal 202 between times T ₂ and T ₃ can be seen. Consequently, as allowed 4B it can be seen, the controller implementing the control routine described above 100 a compensation of setpoint changes in a non-periodic wireless control system in a robust manner. Since disturbance variable circuits can be measured and included in the control action, the controller implementing the control routine described above allows 100 also a compensation of change-over changes in the control output in a non-periodic wireless control system.

It should be noted that the simple PI controller configuration of 4A the output of the filter 116 is used directly as a reset contribution to the control signal, and in this case the reset contribution of a closed-loop control routine (eg, the continuously updated filter equation presented above) can be used to determine if the process is showing steady-state behavior, an accurate representation of the Give process response. However, other processes, such as dead-time dominant processes, may require the integration of additional components in the controller 4A to model the expected process response. With respect to processes that are well represented by a first order model, the process time constant can generally be used well to determine the reset time for the PI (or PID) controller. More specifically, when the reset time is set to the process time constant, the reset contribution generally clears the proportional contribution, so that the control routine 100 reflects the expected process response over time. In the in 4A As illustrated, the reset contribution may be effected by a positive feedback network with a filter having the same time constant as the process time constant. While other models may be used, the positive feedback network, filter or model provides a convenient mechanism for determining the expected response of a process with a known or approximate process time constant. For those processes that require PID control, the differential contribution, also known as rate, can only be recalculated to the PID output and updated when a new measurement is received. In these cases, the differential calculation may use the elapsed time since the last new measurement. Some examples of controllers that can use other controller components to control more complex processes based on a non-periodic reception of process metrics, but which use the filtering technique of 4A to provide a more robust control in response to setpoint changes will be described below in connection with FIGS 5 - 8th described.

Now referring to 5 , an alternative controller (or rule element) 120 , configured in accordance with the control technique as described above, is in many respects similar to that in 4A illustrated controller 100 similar. As a result, common elements with the same reference numbers are identified to both controllers. The controller 120 however, includes an additional element in the control routine that determines the expected process response between measured value transmissions. In this case, the process can 101 be characterized as having a considerable amount of dead time, and thus is a dead time unit or a block 122 included in the controller model for deadtime compensation. The integration of the deadtime unit 122 generally helps to get a more accurate representation of the process response. More specifically, the dead time unit 192 may be implemented in any desired manner and may include or utilize methods common to Smith Predictors or other known rule routines. However, the continuously updated filter works in this situation 116 and the switch module 118 in the same way as above with respect to the controller 100 from 4A to provide robust control in response to setpoint changes.

6 shows another alternative controller (or rule element) 130 which differs from the one in 4A controller described above 100 this distinguishes a differential, or rate, contribution component in the controller 130 is integrated. Integrating the differential contribution includes that provided by the controller 130 For example, the control routine implements an additional feedback mechanism so that in some cases a proportional-integral-derivative (PID) control scheme is implemented.

The control routine or technique of 6 includes a differential contribution that is similar in some ways to the above in connection with the integral contribution of 4A is configured to receive non-periodic or otherwise unavailable updates to the process measurement value. The differential contribution may be restructured to be based on the elapsed time since the last measurement update. In this way, a peak in the differential contribution (and the resulting output signal) is avoided. More specifically, the differential contribution of 6 comes with a differential block 132 determines the error signal from the summation block 108 receives in parallel to the elements dedicated to the proportional and integral contributions. While other PID configurations may be used (eg, a serial configuration), the proportional-integral and derivative contributions are made on a summation block 134 combined, as in 6 shown.

wobei

e_N

= Aktueller Fehler

e_N-1

= Letzter Fehler

ΔT

= Verstrichene Zeit seit Übermittlung eines neuen Wertes

O_D

= Controller-Differenzialterm

K_D

= Differenzialgewinnfaktor

To accommodate unreliable transmissions and, more generally, the unavailability of measurement updates, the derivative contribution is held at the last determined value until receipt of a measurement update, such as the new value flag from the communication stack 80 is displayed. This technique allows the control routine to continue a periodic flow according to the normal or established drain rate of the control routine. After receiving the updated measured value, the differential block 132 , as in 6 illustrates the differential contribution according to the following equation:

in which

e _N

= Current error

e _N-1

= Last error

.DELTA.T

= Elapsed time since transmission of a new value

O _D

= Controller differential term

K _D

= Differential gain factor

With this technique for determining the differential contribution, the process variable metric updates (ie, the control input) may be lost for one or more expiration periods without production of output spikes. When the communication is restored, then the term (e _N -e _N-1 ) in the differential contribution equation can produce the same value as that generated in the standard differential contribution calculation. However, for a standard PID technique, the divider in determining the differential contribution is the expiration period. In contrast, the control technique uses the elapsed time between two successfully received readings. At an elapsed time greater than the expiration period, the control technique produces a smaller differential contribution, and reduced peaks, than the standard PID technique.

To facilitate determining the elapsed time, the communication stack may 80 the above-described new value flag the differential block 132 as in 6 provide shown. Alternative examples may include or involve detection of a new measurement, or update, based on its value. Similarly, the process measurement may be used in place of the error in the calculation of the proportional or derivative component. More generally, the communication stack 80 may be any software, hardware or firmware (or any combination thereof) for implementing a communication interface with the process 101 include or integrate, including any field devices in the process 101 , Process control items outside the controller, and so on in the controller 130 from 6 However, the continuously updated filter works 116 and the switch module 118 in the same way as above with respect to the controller 100 from 4A to provide robust control in response to setpoint changes.

An actuator or other downstream element that is used in conjunction with the 3 . 4A and 5 - 6 In addition, the controller may be controlled to receive a control signal with sudden changes, especially after periods of no communication between the controller or control element to the downstream actuator or other element. The resulting rule action may in some cases be abrupt enough to affect plant operations, and such abrupt changes may result in inappropriate levels of instability.

The potential for abrupt rule changes due to loss of communication between the controller and the downstream element may be realized by integrating actual downstream data rather than the controller output during the process last period of time when determining the feedback contribution / contributions to the control signal. Generally speaking, such actual downstream data provides a feedback indication of a response to the control signal and thus may be measured or calculated by a downstream element (eg, a process control module) or a device (eg, an actuator) that receives the control signal. Such data is provided in place of an implied response to the control signal, such as the controller output from the last run. As in the 4A and 5 - 6 shown receives the continuously updated filter 116 the control signal 105 as an implied indication of the downstream reaction. The use of such implied data effectively assumes that the downstream element, such as an actuator, has received the communications of the control signal and thus responds appropriately to the control signal. The actual feedback data also differs from other response indicators, such as the measured value of the controlled process variable.

7 shows an exemplary controller 140 which receives actuator position data from a downstream device or element in response to the control signal. The downstream device or element often corresponds to an actuator that provides an actuator position reading. More generally, the downstream device or element may correspond to a PID control block, rule selector, divider, or other device or element governed by the control signal. In the exemplary case shown, the actuator position data is provided as an indication of the response to the control signal. Thus, the actuator position data from the controller 140 in periods of continued execution of the control routine despite the absence of measurement updates of the process variables. This can be a continuously updated filter 116 the actuator position data via a communication stack 146 receive, which provides an interface for incoming feedback data. In this exemplary case, the feedback data includes two indications of responses to the control signal, the actuator position, and the process variable.

wobei

F_N

= Neuer Filterausgang

F_N-1

= Filterausgang letzer Ablauf

A_N-1

= Controller Ausgang letzer Ablauf

ΔT

= Controller Ablaufperiode

T_Reset

= Reset Zeit

As in the previous examples, this is a continuously updated filter 116 configured to record situations with missing measurement value updates for the process variable. The continuously updated filter 116 also recalculates its output in such absences, despite the fact that only the filter output produced after receipt of a new measured value flag in the summer 112 is used. However, after receiving a measurement update, the continuously updated filter relies 116 no longer relying on feedback from the control signal to modify its output. Instead, the actual response data from the actuator is used as shown below:

in which

F _N

= New filter output

F _N-1

= Filter output last run

A _N-1

= Controller output last run

.DELTA.T

= Controller expiration period

T _reset

= Reset time

The use of an actual indication of the response to the control signal may help to improve the accuracy of the control techniques, both during periods of periodic communications and after periods of non-periodic or lost communications from the PID controller to the downstream element, for example an actuator. However, the transmission of the actual response indication typically requires additional communications between a field device and the controller when implemented in different devices. Such communications may be wireless, as described above, and thus may be susceptible to unreliable transmissions or performance limitations. Other reasons can lead to the unavailability of the feedback data.

As described below, the control techniques discussed herein may also address situations in which such response indications are not communicated in a periodic or temporal manner, i. the application of the control techniques need not be limited to the lack of measurement updates for the process variable. Instead, the control techniques may advantageously also be used to address situations with missing other response indications, such as the position of an actuator or the output of a downstream control element. In addition, the control techniques may be used to address situations involving the loss, delay, or other unavailability of transmissions from the controller (or control element) to the downstream element, such as a field device (eg, an actuator) or other control element (eg, cascaded PID control, splitter etc.).

The wireless or other unreliable transmission of additional data to the controller or controller (ie, the response indicator or feedback from the downstream element), or The controller or control element (ie the control signal) offers additional potential for communication issues or problems. As described above, feedback from the downstream element (eg, the actuator) may be involved in determining the integral contribution (or other control parameter or contribution). In this example, the control routine relies on two feedback signals rather than the single process variable reported back in the above-described examples. Moreover, if the control signal never reaches the downstream element, the process does not get the benefit of the control scheme. Transmissions of one of these signals may be delayed or lost, and thus the techniques described herein address both eventualities.

The absence of the response indication involved in the filter or other rule calculations may be addressed by holding the indication of the expected response (or other control signal component) until an update is received.

If the control signal does not reach the downstream element, then the response indication (i.e., feedback) from the downstream element will not change. In such cases, the lack of a value change may trigger logic in the controller (or rule element) to maintain the display of the expected response (or other control signal component) until a value change is obtained.

The control techniques may also be implemented in scenarios where actual feedback data is either unwanted or unavailable. The former case may be advantageous in situations where the simplicity of using an implied response to the control signal is useful. For example, communicating the actual feedback data can be problematic or impractical. The latter case may include actuators or other devices that are not configured to provide positional measurement data, as described above. Older devices may not have such capabilities.

To accommodate such devices, a switch or other device may be provided to allow either an implied or an actual response indication to be used by the control techniques. As in 8th Illustrated is a controller 150 with a switch 152 which in turn receives both the implied and the actual response indications. In this case, the controller can 150 be identical to any of the controllers described above insofar as the implementation of the control schemes does not depend on the knowledge of the type of response indicator. The desk 152 can be implemented in software, hardware, firmware, or any combination thereof. The regulation of the switch 152 can from the controller 150 and the implementation of a control routine to be independent. Alternatively or additionally, the control 150 a control signal for configuring the switch 152 provide. Furthermore, the switch 152 be implemented as part of the controller itself and in some cases may be integrated as part of the communication stack or other part of the controller.

The practical implementation of the control methods, system and techniques is not limited to any particular wireless architecture or communication protocol. Suitable exemplary architectures and communication support schemes are described in U.S. Patent Application Serial No. 11 / 156,215, filed June 17, 2005, entitled "Wireless Architecture and Support for Process Control Systems," the entire disclosure of which is incorporated herein by reference. In fact, the modifications to the control routines are well suited for any context in which the control routine is implemented in a periodic fashion, but without process variable metric updates for each rule iteration. Other contextual examples are cases in which a sampled value is provided irregularly or less frequently, for example an analyzer or laboratory samples.

The practical implementation of the control technique is not limited to use with single input / single output PID control routines (with PI and PD routines) but may be applied to a variety of different multi-input and / or multi-output control schemes and cascaded control schemes. More generally, the control technique may also be applied in the context of any closed-loop model-based control routine using one or more process variables, one or more process inputs, or other control signals, such as Model Predictive Control (MPC).

9 illustrates another exemplary control system using the principles described herein, but configured to be a controller 300 in the form of a speed-based controller. In the exemplary system of 9 the controller receives 301 a setpoint signal from, for example, one of the workstations 13 ( 1 and 3 ) or from another source within or in communication with the process control system (s) and generates one or more control signals 305 that the process 301 from an output of the controller 300 to be provided. In addition to the receipt of the control signal 305 can the process 301 also measured or unmeasured Be exposed to interference, as shown schematically by the arrow 304 in 4 is shown. Depending on the type of process control application, the setpoint signal may be generated at any time during the process control 301 changed, such as by a user, an adjustment routine, etc. The process control signals 305 Of course, they may regulate an actuator in conjunction with a valve or may control any other field device to provide an answer in the flow of the process 301 to influence. The answer of the process 301 to changes in the process control signals 305 is from a transmitter, sensor or other field device 306. measured or recorded, for example, any of the in 3 illustrated stations 60 - 64 can correspond. The communication link between the transmitter 306. and the controller 300 can include a wireless connection and is in 9 illustrated by a dashed line. However, this connection can also be a wired communication connection or another type of communication connection. It is assumed, for the purpose of discussion, that the transmitter 306. that measures the controlled process variable (ie, the controlled variable), or a proxy variable that correlates to the controlled process variable, at a slow or intermittent refresh rate. This slow update rate may be periodic or non-periodic, and is believed to be of the same order of magnitude as the process response rate of the process dynamics associated with the controlled process variable. Thus, the process variable measurements are provided once per time interval that is greater than the response time of the process, once per time interval, similar to the process response time, or once per time interval that is slightly less than the process response time. Thus, in some cases, this refresh rate may be ½ to ¼ of the process response rate (the reverse of the process response time).

In an in 9 illustrated embodiment, the controller 300 implement a closed-loop single-input / single-output control routine, such as a PI control routine, which is one form of a PID control routine. Accordingly, the controller includes 300 multiple standard PI controller elements, including a communication stack 380 , and a control signal generation unit with a summation block 308 , a proportional gain element 310 and another summation block 312 , The control routine 300 also includes a direct integral feedback path including a filter 316 and an integral output switch comprising a selection block 318 includes. In this case, the PI controller is from 9 however, configured to perform position or derivative control calculations on the proportional and integral components of the control signal. Thus, the controller includes 300 also a differential block 320 , which is arranged in the proportional component calculation path, a summer 322 which is arranged in the integral component calculation path, and a block 324 which uses the derivative computed control component at its input to control the signal 305 to create. Generally speaking, the block 324 scales the change of the position (velocity) control signal as in the controller 300 or otherwise converts that signal to an analog or digital signal that is sent to the controller to instruct the controller to move a certain amount in one direction or another over a certain period of time. This block 324 For example, it may send a pulse width modulated signal, a pulsed signal, a digital signal indicating an on-time, or any other signal indicating to the controller a magnitude of a change in position over time.

As in 9 illustrated, is the integral filter 316 with the output of the summier 342 coupled, in turn, for receiving the output of the summer 312 is coupled while the block 318 of the switch with the output of the filter 316 is coupled and the summation block 312 the integral or reset contribution or component of the controller 300 provides generated control signal.

At every iteration or operation of the controller 300 compares the summation block 308 the setpoint signal with the last received process variable reading from the communication stack 380 in the controller 300 is provided to generate an error signal (e). The proportional gain element or block 310 acts on the error signal e, for example by multiplying the error signal e by a proportional gain value K _p for generating a proportional contribution or component of the speed control signal. The difference block 320 then determines the change in the proportional gain value since the last controller iteration by determining the difference between the current output of the gain block 310 and the most recent value of the winning block 310 (produced at the last or immediately preceding controller iteration). The summation block 312 then combines the output of the change unit 320 (the velocity-based proportional contribution) with the integral or reset contribution or component of the integral signal feedback control signal generated by the integral feedback path to produce a velocity control signal 326 that is the starting block 324 provided.

Significantly, however, the summer produce 322 , the filter 316 and the block or switch 318 in the integral feedback path of the controller 300 the integral or reset Contribution component of the control signal in the following manner. Here is the summer 322 for receiving the output of the summer 312 (ie, the rate-based control signal representing the change in the position of the movable control element) coupled at each controller iteration and sums this value to the previous output S of the summer 322 (generated at the last iteration of the controller 300 ), thereby in fact integrating or summing the change in the change of the output signal over a certain period of time. The new output S of the summer 322 becomes the integral filter 316 provided an indication of the expected process response to the control signal 305 generated, in 9 indicated as R The filter 316 puts this expected process response signal R to the switch or block 318 ready. As in 9 the switch or block will be displayed, felt and locked 318 the output of the filter 316 at the output of the switch or block 318 Whenever a new process variable reading has been received, it otherwise applies a zero (0,0) value to the summer 312 as an integral rule contribution to these rule iterations where no new process variable reading is available. Thus, the output of the switch 318 provided as an integral control contribution to produce a new control signal at each controller iteration, the output of the filter 316 only in controller iterations where a new process variable reading is for use by the controller 300 is available, and is otherwise zero (0,0). Every time the one from the communication stack 380 generated new value flag is set (indicating that a new process variable reading is on the controller 300 is available), sets the summer 322 its output to zero and starts summing over a new period of time. This is how the totalizer sums up 322 in fact, the change in the control output signal over each controller iteration between process variable measurement updates and resets whenever (during the controller iteration after) when a new process variable measurement value update on the controller 300 Will be received.

The expected process response to changes in the control signal generated by the filter 316 , can be approximated with a first order model as described in more detail below. More generally, however, the expected process response may be with any suitable model of the process 301 is generated and is not limited to a model that is in a feedback path of the controller 300 integrated, or a filter or model associated with determining an integral or reset contribution to a control signal. For example, controllers that use a model to provide the expected process response may include a differential contribution, such that the control routine 301 PID control scheme implemented. An example including an exemplary differential contribution will be described below in connection with FIG 10 described.

In any event, the control technique described below allows the use of the positive feedback path to determine the reset or integral contribution when the controller 300 receiving slow or non-periodic updates to the process variables, and further enables a robust controller response in the event of setpoint changes or override changes occurring between receipt of new process variable measurements. Especially, the filter 316 is for calculating a new indication or value of an expected process response each time the controller expires 300 regardless of whether this output of the filter 316 ever the summation block 312 is provided as an integral component of the control signal. Consequently, the output of the filter becomes 316 at each expiration cycle, the controller routine recreates, though only the output of the filter 316 which is generated immediately after (or during the expiration cycle in which) the controller 300 a new process value update from the communication stack 380 receives from the controller 300 as integral or reset contribution in the totalizer 312 used.

wobei

R_N

= Neuer Filterausgang

R_N-1

= Filterausgang letzter Ablauf

S_N-1

= Intergralpfad Summiererausgang letzter Ablauf

ΔT

= Controller Ablaufperiode

e^TReset

= Integralzeitperiode

In particular, the new display of the expected response R will be like the filter 316 is generated at each controller expiration cycle from the current summer output S (ie the summed change in the control signal output by the summer 312 since the last process variable reading update), the display of an expected response from the filter 316 is generated during the last (ie immediately preceding) controller expiration cycle, and the controller expiration period is calculated. Consequently, the filter becomes 316 herein described as continuously updated because it is executed to generate a new process response estimate at each controller expiration cycle. An example equation follows that of the continuously updated filter 316 can be implemented to generate a new expected process response or filter at each controller expiration cycle:

in which

R _N

= New filter output

R _N-1

= Filter output last process

S _N-1

= Integral path totalizer output last process

.DELTA.T

= Controller expiration period

e ^TReset

= Integral time period

It will be noted here that the new filter output R _{N is} iteratively determined to be the most recent filter output R _N-1 (ie, the current filter output value) plus a decay component which is the difference between the summed change in the current controller output R _{N. 1} multiplied by a factor which depends on the reset time T _Reset and the controller expiration period ΔT. By using a filter that is continually updated in this way is the control routine 300 better able to determine the expected process response in computing the integral control signal input when a new process variable reading is received, thereby better responding to changes in setpoint or other disturbance upsets that occur between receipt of two process variable measurements. However, this integral path calculation prevents wind up of the control system in the presence of slowly received or intermittent process variable feedback measurements. More specifically, it will be noted that changing the setpoint (without receiving a new process measurement) will immediately result in a change in the error signal at the output of the summer 308 resulting in the proportional contribution component of the speed control signal 326 and thus the control signal 305 will be changed. Consequently, the summer increases 392 its output S by that amount and the filter 316 then begins to generate a new expected response of the process to the changed control signal, and thus updates its output before the controller 300 receives a new process reading. If then the controller 100 receives a new process reading and a sample of the filter output from the switch 318 to the input of the summer 312 snapped to use as an integral or reset contribution component of the control signal, the filter has 316 iterates on an expected process response, at least to an extent based on the response of the process 301 to the change of the setpoint on the basis of a previously sent control signal 305 has reacted or contains. This integral value becomes the control signal 326 however, only added when a new process metric is received, to allow that from the summer 308 generated error signal e changes the process variable between times reflecting the process variable readings at the controller 300 be received. For controller iterations between the times a process variable reading is received, the one from the summer 312 provided integral component set to zero. This technique prevents a wind-up of the control system 300 or contributes to such prevention. In fact, those from the filter appreciate 316 integral component generates the process response between the times (controller iterations) to which subsequent process variable feedback is received and, if the actual process variable response is as expected, if a new process variable reading is present on the controller 300 is received, then the integral component brings the value generated in the proportional path to zero. If the expected response of the process differs from the actual process response during that time, then the integral component causes a change in the control signal 326 in order to force a movement of the actuator, thereby correcting the position of the actuator.

In the past, such as systems used in the U.S. Patent Nos. 7,587,252 and 7,620,460 described, the reset contribution filter used in a feedback path of a non-periodically updated controller calculated only a new indication of an expected response when a new process variable reading was available. Thus, the reset contribution filter did not compensate for setpoint changes or disturbance upsets that occurred between receipt of process variable measurements because the setpoint changes or disturbance upshifts were completely independent of any measurement updates. For example, if a setpoint change or feedforward occurred between two measurement updates, then the expected process response of the controller was likely to be skewed because the calculation of the new display of the expected response to the time since the last measured value update and the current controller output 305 based. Consequently, the filter could 316 does not begin to take into account temporal changes in the process (or control signal) resulting from a set point change (or other feedforward) occurring between the receipt of two process variable measurements at the controller.

One will understand, however, that the control routine 300 from 9 providing an expected process response by basing the calculations on slow or non-periodic measurements while additionally determining the expected response between the receipt of two measurements to account for changes caused by a change in the setpoint (or any measured disturbance , which serves as a connection input to the controller 300 is used). Thus, the control technique described above can accommodate set point changes, uplink actions on measured disturbances, etc. that affect the expected process response and thus can provide a more robust control response. In addition, because it avoids wind-up in the controller, this control technique can operate effectively if the process variable feedback feedback rate is equal to or even less than the reversal of the process response time (ie, the times between feedback measurements received on the controller are greater than the process response time).

As you will understand, the in 9 illustrated control technique an indication of an expected response via the continuously updated filter 316 (eg the reset contribution filter) for each expiration of the rule block or routine 300 , Here the controller configures 300 the continuously updated filter 316 to calculate a new indication of an expected response for each run of the rule block. However, to determine if the output of the filter 316 as input to the summation block 312 is to be used, the communication stack processes 380 and, in some examples, the update detection module 82 ( 3 ), the incoming data from the sender 306. for generating a new value flag for the integral output switch 318 and for the summer 326 when a new process variable reading is received. This new value flag informs the switch 318 to sample and snap the filter output value for this controller iteration to the input of the summer 312 , Otherwise, the switch provides 318 the summer 312 a zero (0.0) value as an integral contribution value.

Regardless of whether a new value flag is submitted, the continuously updated filter sets 316 the calculation of an expected response indication for each iteration of the control routine. This new indication of an expected response will be sent to the integral output switch 318 supplied at every expiration of the control block. Depending on the presence of the new value flag, the integral output switch switches 318 between allowing the new display of the expected response from the continuously updated filter 316 on passing to the summation block 312 to get a zero value at the input to the summation block 312 to keep. More specifically, when a new value flag is transmitted, then the integral output switch leaves it 318 to that last or currently calculated display of the expected response from the continuously updated filter 316 to the summation block 312 is allowed through. Conversely, if the new value flag is not present, then the integral output switch is 318 the summer 312 a zero value.

After or if a new process variable reading on the process controller 300 is received and the output R of the continuous filter 316 in the summer 312 is used, then the time since the last communication is set to zero (0) and the continuous filter output R is set to zero. Likewise, the output of the summer 322 set to zero (0). Furthermore, in these situations, the summer 312 the continuous filter output R from the output of the block 320 subtract to the new control signal 326 depending on the way or order in which the block is generated 320 performs a difference calculation.

This control technology allows it to be that continuously updated filter 316 the expected process response continues to be modeled regardless of whether a new measurement is being transmitted. If the control output changes due to a result of a setpoint change or a stall action based on a measured disturbance, regardless of the presence of a new value flag, then the continuously updated filter reflects 316 the expected process response by calculating a new indication of an expected response at each rule routine iteration. The new indication of the expected response (ie, the reset contribution or integration component) is included in the controller output computations only when a new value flag is communicated (via the integral output switch 318 ), the wind-up of the controller in response to slowly received process variable measurements on the controller 300 prevents or reduces.

It should be noted that the simple PI controller configuration of 9 the output of the filter 316 In this case, the reset contribution of a closed-loop control routine (eg, the continuously updated filter equation presented above) may provide an accurate representation of the process response in determining whether the process is in steady-state behavior shows. However, other processes, such as dead-time dominant processes, may require the inclusion of additional components in the controller 9 as in the 5 and 6 by incorporating a dead time unit in the integral calculation path to model the expected process response. With respect to processes that are well represented by a first order model, the process time constant can generally be used to determine the reset time for the PI (or PID) controller. More specifically, if the reset time is equal to the process time constant, then the reset contribution generally clears the proportional contribution, so that, over time, the control routine 300 reflects the expected process response. In the in 9 As illustrated, the reset contribution may be effected by a positive feedback network with a filter having the same time constant as the process time constant. While other models may be used, the positive feedback network, filter, or model provides a convenient mechanism for determining the expected response of a process with a known or approximated process time constant. For those processes that require PID control, the differential contribution, also known as rate, may be recalculated to the PID output, and only then be updated when a new reading is received. In these cases, the differential calculation may use the elapsed time since the last new measurement. An example of a controller that can use other controller components to control more complex processes with a non-periodic reception of process measurements, but that uses the filtering technique of 9 to provide a more robust control in response to setpoint changes will be discussed below in connection with 10 described.

In particular shows 10 an alternative controller (or rule element) 400 that is from the controller 300 as in above 9 in that a differential, or rate, contribution component into the controller differs 400 is involved. Including the differential contribution includes that provided by the controller 400 For example, the control routine implements an additional feedback mechanism so that in some cases a proportional-integral-derivative (PID) control scheme is implemented.

The control routine or technique of 10 includes a differential contribution that is similar to that described above in connection with the systems of the 7 and 8th described for recording slow, non-periodic or otherwise unavailable updates of the process variable reading. The differential contribution may be reconstructed based on the elapsed time since the last measurement update. In this way peaks in the differential contribution (and the resulting output signal) are avoided. More specifically, the differential contribution in the system of 10 comes with a differential block 432 determines the error signal (multiplied by the proportional gain K _p ) from the winning block 310 in parallel with the elements dedicated to the proportional and integral contributions, and generates a derivative rule component O _D which is then applied to a modifier block 433 provided. The change block 433 determines the change of the differential control component O _D since the last controller iteration and sets this change value to a summer 434 ready this change in the differential rule component to the output of the summier 312 summed or added to produce the change of the control signal. In this case, the summer is 322 in the integral contribution calculation path with the output of the summer 434 connected. The components of 10 that also in 9 Illustrated are working in relation to 9 described way. Here it becomes apparent that the differential block 432 only operates to compute a new differential component O _D only for controller iterations in which a new value flag is received therein (indicating that a new value of the process variable reading has been received at the controller). This operation indeed holds the output of the change block 434 for all controller iterations to zero, during or at which no new process variable reading on the controller 400 Will be received.

wobei

e_N

= Aktueller Fehler

e_N-1

= Letzter Fehler

ΔT

= Verstrichene Zeit seit Übermittlung eines neuen Wertes

O_D

= Controller-Differenzialterm

K_P

= Proportionalgewinnfaktor

K_D

= Differenzialgewinnfaktor

To accommodate unreliable transmissions and, more generally, the unavailability of measurement updates, the derivative contribution O _{D is held} at the last determined value until a measurement update is received, such as by the new value flag from the communication stack 380 displayed. This technique allows the control routine to continue with a periodic flow according to the normal or established drain rate of the control routine. After receiving the updated measured value, the differential block can 432 , as in 10 illustrates the differential contribution according to the following equation:

in which

e _N

= Current error

e _N-1

= Last error

.DELTA.T

= Elapsed time since transmission of a new value

O _D

= Controller differential term

K _P

= Proportional gain factor

K _D

= Differential gain factor

If desired, the differential component calculation block 432 of course directly to the output of the summer 308 can be connected to receive the error signal, and the Differenzgewinngewinnterm K _D can be set so that a differential gain with the proportional gain K _{P is} integrated. With this technique for determining the differential contribution, the process variable metric updates (ie, control input) may be lost, or may not be available for one or more consecutive expiration periods without production of output peaks, allowing bumpless recovery. If the communication is restored or if a new process variable reading is received at the controller, then the term (e _N -e _N-1 ) in the differential contribution equation may produce the same value as that generated in the standard differential contribution calculation. However, for a standard PID technique, the divider in determining the differential contribution is the expiration period. In contrast, the control technique uses the elapsed time between two successfully received readings. With an elapsed time greater than the expiration period, the control technique generates a smaller differential contribution, and reduced peaks, as the standard PID technique.

To facilitate the determination of elapsed time, the communication stack may 80 the above-described new value flag the differential block 432 as in 10 provide shown. Alternative examples may include or involve detection of a new measurement, or update, based on its value. The process measurement may also be used instead of the error in the calculation of the proportional or derivative component. More generally, the communication stack 380 may be any software, hardware or firmware (or any combination thereof) for implementing a communication interface with the process 301 include or integrate, including any field devices in the process 301 , Process control elements outside the controller, etc. in the controller 400 from 10 work the continuously updated filter 316 and the switching module 318 however, in the same way as above with respect to the controller 300 from 9 to provide robust control in response to setpoint changes.

The practical implementation of the control methods, systems and techniques described herein are not limited to any particular wireless architecture or communication protocol. Suitable exemplary architectures and communication support schemes are described in U.S. Patent Application Serial No. 11 / 156,215, filed June 17, 2005, entitled "Wireless Architecture and Support for Process Control Systems," the entire disclosure of which is incorporated herein by reference. In fact, the modifications to the control routines are well suited for any context in which the control routine is implemented in a periodic fashion but without process variable metric updates for each control iteration. Other relationships include those where a sampled value is provided irregularly or less frequently by, for example, an analyzer, or via laboratory samples.

The practical implementation of the control technique is not limited to the use of single input / single output PID control routines (including PI and PD routines) but may be applied to a variety of different multi-input and / or multi-output control schemes and cascaded control schemes. More generally, the control technique may also be applied in the context of any closed-loop model-based control routine involving one or more process variables, one or more process inputs, or other control signals, such as Model Predictive Control (MPC).

11 - 14 12 show diagrams of a simulated operation of the control routines described herein (in particular those of FIG 10 ) in comparison to a prior art controller using a standard speed scheme of a PID control algorithm to illustrate the effectiveness of the current control routine in situations where the process response time is similar to, or even less than, the time between updates of the measured value of the regulated one Process variable is. The curves of 11 - 14 illustrate simulated control examples using only primary control, although other types of control could be used, for example override control. Generally speaking, each of the curves in the 11A . 12A . 13A and 14A illustrates the operation of the prior art standard speed-based PID control algorithm using a wired feedback configuration (this operation is illustrated on the left side of the graph) in which a new process variable reading is available at each controller iteration and a wireless one Configuration (this operation is illustrated on the right side of the curve). The 11A and 13A however, illustrate control situations in which the feedback rate or time between process variable measurements is 8 seconds and in which the process response time is 8 seconds while the 12A and 14A illustrate the operation of the prior art controller in which the feedback rate or time between process variable measurements is 8 seconds and in which the process response time is 3 seconds. Likewise illustrate the 11 and 12 the controller operation in response to setpoint changes while the 13 and 14 illustrate the operation of the same controllers in response to disturbance changes. For comparison, the curves of 11B . 12B . 13B and 14B illustrate the operation of the speed-based PID algorithm described herein in the same process control situations as those of FIG 11A . 12A . 13A and 14A ,

Generally speaking, the following parameters have been included in the 11 - 14 Simulated rule operations were used and these tests were run for wired and wireless inputs and for changes in set point and unmeasured disturbances as explained above. The control and process simulations used in the test were set up as follows:

Test for process response of 8 seconds

• Primary processes (same profit and dynamics) Process gain = 1 Process time constant = 8 seconds Process dead time = 0 seconds
• PID tuning for primary (lambda factor 1.0) Proportional gain = 1 Integral gain = 7.5 repetitions / min

Test for process response of 3 seconds

• Primary process (same profit and dynamics) Process gain = 1 Process time constant = 3 seconds Process dead time = 0 seconds
• PID tuning for primary (lambda factor 1.0) Proportional gain = 1 Integral gain = 20 repetitions / min

Module flow rate

• 0.5 sec for all tests

Wireless communication update rate

• 8 sec periodically for all tests

disturbance input

• Affects only primary readings
• Profit = 1

As in the 11A and 13A illustrates, the state-of-the-art speed-based PID control algorithm works reasonably satisfactorily in response to setpoint changes (FIG. 11A ) and on disturbance variable changes ( 13A ) in both the wired configuration and in a wireless configuration where the process response time equals the interval between process variable measurements (both set to 8 seconds). However, as by the circled parts of the curves of 11A and 13A implied, this control technique results in the valve position undergoing significant changes during the wireless control response. As in the 11B and 13B illustrates, the current control technique described herein works slightly better in these situations (setpoint change in FIG 11B and disturbance change in 13B ) and very similar to the operation of the wired configuration.

However, as in the 12A and 14A As illustrated, the state-of-the-art speed-based PID controller operates very poorly and indeed becomes unstable in wireless control in response to setpoint changes and disturbance changes when the process response time is 3 seconds and the process variable update rate is 8 seconds. However, as in the 12B and 14B As illustrated, the current rate-based control routine continues to operate very satisfactorily in these situations, illustrating the effectiveness of the currently described control routine when the process variable measured value update interval time is greater (longer) and even significantly (eg, 2-4 times) greater than the process response time.

As used herein, the term "field device" is to be understood in a broad sense to include a number of devices or device combinations (ie, devices that provide multiple functions, such as a transmitter / actuator hybrid), as well as any (s). includes other device (s) performing a function in a control system. In either case, field devices may include, for example, input devices (eg, devices such as sensors and instruments that provide status, measured value, or other signals indicative of process control parameters such as temperature, pressure, flow rate, etc.), as well as control operators or actuators that respond in response to commands received from consoles and / or other field devices such as valves, switches, flow controllers, and so forth.

It should be understood that portions of any of the control routines or modules described herein may be implemented or executed in a distributed fashion across multiple devices. Thus, portions of a control routine or module may be implemented by different controllers, field devices (eg, smart field devices), or other devices or control elements, if desired. Similarly, the control routines or modules described herein that are to be implemented in the process control system may take any form, including software, firmware, hardware, etc. Any device or element involved in providing such functionality may be generally referred to herein as " Regardless of whether the associated software, firmware or hardware is located in a controller, field device or other device (or collection of devices) in the process control system. A rule module may be any part of a process control system, including, for example, a routine, block, or any element thereof stored on any computer-readable medium. Such control modules, control routines, or any portions thereof (eg, a block) may be implemented or executed by any element or device of the process control system, referred to herein generally as a control element. Rule routines, which may be modules or any part of a rule procedure, such as a subroutine, parts of a subroutine (such as code lines), etc., may be implemented in any desired software format, such as using object-oriented programming, ladder logic, sequential function maps, function block diagrams, or any other software programming language or design paradigm. Likewise, the control routines may, for example, be hard-coded into one or more EPROMS, EEPROMs, application specific integrated circuits (ASICs), or any other hardware or firmware elements. In addition, the control routines can be designed with any design tools, including graphical design tools or any other type of software / hardware / firmware programming or design tools. So can the controller 11 for implementing a control strategy or control routine in any desired manner.

Alternatively or additionally, the functional blocks may be stored in or implemented in the field devices themselves or in other control elements of the process control system, which may be the case with systems using fieldbus devices. While the control system has been described herein with a functional block control strategy, the control techniques and system may also be implemented or designed with other conventions, such as ladder logic, sequential function maps, etc., or any other desired programming language or paradigm.

When implemented, any of the software described herein may be stored in any computer-readable memory, such as a magnetic disk, a laser disk, or other storage medium, in RAM or ROM of a computer or processor, etc. Similarly, this software may be provided to a user, a computer Processor or an operator workstation can be provided by any known or desired delivery method, such as on a computer-readable floppy disk or other portable computer storage mechanism or via a communication channel such as a telephone line, the Internet, the World Wide Web, any other local Network or wide area network, etc. (where such delivery is considered to be the same as or interchangeable with the provision of such software via a portable storage medium). Further, this software may be provided directly without modulation or encryption, or may be modulated and / or encrypted with any suitable modulation carrier wave and / or encryption technique before being transmitted over a communication channel.

While the present invention has been described with reference to specific examples, which are intended to illustrate and not limit the invention, it will be obvious to those of ordinary skill in the art that changes, additions or deletions to the control techniques can be made without departing from the spirit and the art Deviating scope of the invention.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 7587252 [0012, 0061, 0096]
• US 7620460 [0012, 0013, 0061, 0096]

Claims (31)

Method for regulating a process that includes: Implement, on a computer processing device, a plurality of iterations of a control routine for generating a control signal that includes at each iteration of the control routine: Generating, with a computer processing device, an integral feedback contribution for use in generating the control signal, including using, at each of the plurality of iterations, an iterative filter to determine a current integral feedback contribution value for the current iteration of the control routine from an integral Feedback contribution value of a previous iteration of the control routine and a value of the control signal; and Using the current integral feedback contribution to generate the control signal for the current iteration of the control routine at each controller iteration receiving a new process response indication, and not using the current integral feedback contribution to generate the control signal during controller iterations; where no new process response indication is received on the control signal; and Use the control signal to control the process. The method of claim 1, further comprising generating a proportional contribution at each iteration and using the proportional contribution at each iteration to generate the control signal. Method according to one of the preceding claims, in particular claim 1, wherein the process response display is a measured value for a process parameter, which is influenced by the control signal, wherein preferably the process parameter is a process variable which is controlled by a field device, which responds to the control signal. The method of claim 1, wherein determining the integral feedback contribution comprises generating the integral feedback contribution value based on the difference between the control signal for the current iteration of the control routine and the integral feedback contribution value includes the previous iteration of the control routine multiplied by a factor in response to a reset time and a controller expiration period. The method of claim 1, wherein implementing multiple iterations of a control routine for generating a control signal at each iteration of the control routine generates the control signal based on a setpoint, a most recent measurement of a process variable, and the integral feedback contribution includes. Method according to one of the preceding claims, in particular claim 1, wherein implementing a plurality of iterations of a control routine for generating a control signal in each iteration of the control routine generating a proportional component of a setpoint, a last received process response display and a proportional gain value and generating the control signal with a Difference between the proportional component generated at the current iteration and the proportional component generated at a previous iteration. The method of claim 1, wherein generating the integral feedback contribution for use in generating the control signal comprises determining a current integral feedback contribution value for the current iteration of the control routine from an integral feedback contribution value includes prior iteration of the control routine and a summed value of the control signal for all previous iterations since the last iteration at which a new process response indication was received. The method of claim 1, wherein generating the integral feedback contribution for use in generating the control signal comprises determining a current integral feedback contribution value for the current iteration of the control routine from an integral feedback contribution value includes prior iteration of the control routine and a summed value of the control signal for all previous iterations since the last iteration at which a new process response indication was received. A process controller that generates a control signal for controlling a process variable at each of a plurality of controller iterations of the process controller, comprising: a communication unit that receives a new value of the process variable less than each of the plurality of iterations of the process Controller receives; a proportional control component that generates a proportional control signal value at each of the iterations of the process controller, including: a first summer that determines a difference between a setpoint for the process variable and a received value of a process variable, and a proportional gain unit coupled to the summer; an integral control component that generates an integral control signal value at each of the iterations of the process controller including an iterative filter that provides a preliminary integral control component at each iteration of the process controller based on a previous value of the preliminary integral control component generated at a previous integration of the process controller and determined based on the control signal for the current iteration of the process controller; and a switch coupled to the interactive filter receiving the preliminary integral control component and another value, the switch having the function of performing the task of the interactive filter in process controller iterations associated with receiving a new value of the process variable at the communication unit as an integral control signal value, to provide generated preliminary integral control component and which provides the further value as the integral control signal value in controller iterations not associated with the receipt of a new value of the process variable at the communication unit; and a second summer that sums the proportional control signal value and the integral control signal value at each process controller iteration to generate the control signal. The process controller of claim 9, wherein the integral control component further comprises a third summer coupled to the iterative filter, the third summer summing the control signal for previous controller iterations to provide a summed control signal value, and wherein the third summer summed the one Provides control signal value as input to the iterative filter. The process controller of any of claims 9 or 10, in particular claim 10, wherein the third summer resets the summed control signal upon receipt of a new value of the process variable at the communication unit, preferably wherein the third summer resets the summed control signal to zero. Process controller according to one of claims 9 to 11, in particular according to claim 10, wherein the further value is zero. The process controller of any one of claims 9 to 12, in particular claim 10, wherein the proportional control component includes a difference unit coupled to the proportional gain unit, preferably wherein the difference unit is coupled between the proportional gain unit and the second summer and a difference value between the output of the proportional gain unit determines the previous controller iteration and the output of the proportional gain unit at the current controller iteration and provides the difference value to the second summer as a proportional control signal value. The process controller of any one of claims 9 to 13, in particular claim 9, further including a control signal conversion unit coupled to the second summer that converts the control signal into an output control signal to be sent to control a device within a process, preferably Control signal represents a change of the output control signal to be sent to the process. The process controller of claim 9, further comprising a differential control component that determines a differential control signal value, the differential control component including a differential gain unit coupled to the first summer, and a second differential unit coupled to the differential gain unit which determines a further difference value between the output of the differential gain unit from a previous controller iteration and the output of the differential gain unit at the current controller iteration, and provides the further difference to the second summer as the differential control signal value, and wherein the second summer outputs the differential control signal value with the integral control signal value and the proportional control signal value to generate the control signal. The process controller of any one of claims 9 to 15, in particular claim 9, wherein the further value is an integral control signal value output by the switch in a previous controller iteration. A method of generating a rate-based process control signal at each of a plurality of iterations of a control routine, comprising: receiving, via a computer processing device, a new value of the controlled process variable at less than each of the plurality of iterations of the control routine; Generating, with a computer processing device, at each of the plurality of iterations of the control routine, a difference-based integral feedback contribution for use in generating the control signal, including summing the control signal generated at each iteration of the control routine since the last iteration of the control routine, at a new process variable value was received to generate a summed control signal, providing the summed control signal to an iterative filter, and using, at each of the plurality of iterations, the iterative filter to determine a current integral feedback contribution value for the current iteration of the control routine from an integral feedback contribution value of a previous iteration of the control routine and the summed control signal; and using the current integral feedback contribution value to generate the control routine for the current iteration of the control routine at each iteration at which a new process variable value is received, and not using the current integral feedback contribution value to generate the control signal during iterations in which no new process variable value is received from the process; and using the control signal to control the process variable. The method of generating a velocity-based process control signal of claim 17, further comprising generating, with a computer processing device, a differential-based proportional contribution in each of the iterations of the control routine and using the proportional contribution in each of the iterations of the control routine to generate the control signal. Method for generating a speed-based process control signal according to one of claims 17 or 18, in particular claim 17, wherein the new process variable value is a measured value of a process parameter influenced by the control signal. A method of generating a velocity-based process control signal according to any one of claims 17 to 19, in particular claim 17, wherein determining the integral feedback contribution comprises generating the current integral feedback contribution value based on the difference between the summed control signal for the current iteration the control routine and the integral feedback contribution value of the previous iteration of the control routine multiplied by a factor that depends on a reset time and a controller expiration period. A method for generating a velocity-based process control signal according to any one of claims 17 to 20, in particular claim 17, wherein the non-use of the current integral feedback contribution value for generating the control signal in iterations in which no new process variable value is received by the process, using a fixed value as the current integral feedback contribution to generating the control signal in iterations where no new process variable value is received by the process. A method of generating a velocity-based process control signal according to any one of claims 17 to 21, in particular claim 17, wherein the fixed value is zero. A velocity-based process controller that generates a control signal for controlling a process variable at each of a plurality of controller iterations of the process controller, comprising: a communication unit that receives a new value of the process variable on less than each of the plurality of process controller iterations: an integral control component that generates an integral control signal value at each of the iterations of the process controller, including an iterative filter that determines a preliminary integral control component at each iteration of the process controller based on a previous value of the preliminary integral control component generated at a previous iteration of the process controller and based on the current process controller iteration control signal; and a switch coupled to the iterative filter receiving the preliminary integral control component and another value, the switch having the task of providing the temporary integral control component generated by the iterative filter in process controller iterations that receives a new value of the process variable is associated at the communication unit as the integral control signal value and which provides the further value as an integral control signal value in controller iterations not associated with the receipt of a new value of the process variable at the communication unit; and a control signal generator coupled to receive the integral control signal value to generate a control signal for use in controlling the process at each of the controller iterations. The velocity-based process controller of claim 23, further comprising a proportional control component including a proportional control signal value at each of the iterations of the process controller, including, a first summer determining a difference between a set value for the process variable and a received value of the process variable, and a proportional gain unit coupled to the summer; and wherein the control signal generator includes a second summer that sums the proportional control signal value and the integral control signal value at each process controller iteration to generate the control signal. A speed-based process controller according to any of claims 23 or 24, in particular claim 24, wherein the proportional control component includes a difference unit coupled to the proportional gain unit, wherein Preferably, the difference unit is coupled to the proportional gain unit and the second summer and determines a difference value between the output of the proportional gain unit from a previous controller iteration and the output of the proportional gain unit at the current controller iteration and provides the difference value to the second summer as a proportional control signal value. The process controller of claim 23, further comprising a differential control component that determines a differential control signal value, wherein the differential control component includes a differential gain unit coupled to the first summer, and a second differential unit coupled to the differential gain unit determining a further difference value between the output of the differential gain unit from a previous controller iteration and the output of the differential gain unit at the current controller iteration, and providing the further difference value to the second summer as the differential control signal value, and wherein the second summer sums the differential control signal value with the integral control signal value and the proportional control signal value to generate the control signal. The velocity-based process controller of any one of claims 23 to 26, in particular claim 23, wherein the integral control component includes another summer coupled to the iterative filter, the summer summing the control signal for previous controller iterations to produce a summed control signal value, and wherein the summer provides the summed control signal value as an input to the iterative filter. The speed-based process controller of any of claims 23 to 27, in particular claim 27, wherein the summer resets the summed control signal upon receipt of a new value of the process variable at the communication unit, preferably wherein the summer resets the summed control signal to zero. A speed-based process controller according to any of claims 23 to 28, in particular claim 23, wherein the further value is zero. A speed-based process controller according to any one of claims 23 to 29, in particular claim 23, further including a control signal conversion unit coupled to the control signal generator which converts the control signal generated by the control signal generator into an output control signal to be sent for controlling a device within a process , wherein preferably the control signal represents a change in the output control signal to be sent to the process. A computer-readable storage medium containing instructions that cause at least one processor to implement a method as claimed in any one of claims 1 to 8 and / or 17 to 22 when the instructions are executed by the at least one processor.

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