CN105843268B

CN105843268B - Valve positioner with overpressure protection capability

Info

Publication number: CN105843268B
Application number: CN201510017355.6A
Authority: CN
Inventors: B·F·格鲁姆斯特鲁普; L·D·米勒; J·L·斯诺巴杰; A·J·威特科普
Original assignee: Fisher Controls International LLC
Current assignee: Fisher Controls International LLC
Priority date: 2015-01-12
Filing date: 2015-01-12
Publication date: 2020-01-03
Anticipated expiration: 2035-01-12
Also published as: CN105843268A

Abstract

A method for limiting a control pressure provided to an actuator of a valve coupled to a valve positioner provides a drive signal to a pneumatic stage of the valve positioner. The pneumatic stage is configured to control an output pressure of the valve positioner based on the drive signal. A pressure measurement is obtained from a pressure sensor communicatively coupled to the valve positioner, and an abnormal pressure is detected based on the pressure measurement. In response to detecting the abnormal pressure, controlling the drive signal to limit the output pressure of the valve positioner, wherein the output pressure provides a control pressure to the actuator.

Description

Valve positioner with overpressure protection capability

Technical Field

The present invention relates generally to process control systems and, more particularly, to providing overvoltage protection for process control devices in process control systems.

Background

Process control systems, such as distributed or scalable process control systems (e.g., for use in chemical, petroleum or other processes), typically include one or more process controllers communicatively coupled to one or more field devices via analog, digital or combined analog/digital buses. The field devices may include, for example, control valve assemblies (e.g., control valves, actuators, valve controllers), valve positioners, switches and transmitters (e.g., temperature, pressure and flow rate sensors), perform functions within the process such as opening or closing valves, measuring process parameters, and performing basic diagnostics. The process controller receives process measurements indicative of process measurements made by the field devices and/or other information pertaining to the field devices, and uses this information to execute or implement one or more control routines to generate control signals that are sent over the buses to the field devices to control the operation of the process. The information from each field device and controller is typically made available to one or more applications executed by one or more other hardware devices (e.g., a host or user workstation, a personal computer, or a computing device) to enable an operator to perform any desired function with respect to the process, such as setting process parameters, observing the current state of the process, modifying the operation of the process, etc.

Process control systems typically employ electro-pneumatic controllers (e.g., electro-pneumatic positioners) to control process control devices (e.g., control valves, pumps, dampers, etc.) operating within the process control system. Electro-pneumatic controllers are generally configured to receive one or more control signals and convert those control signals into a pressure provided to a pneumatic actuator to cause a process control device coupled to the pneumatic actuator to perform a desired operation. For example, if a process control routine requires a pneumatically actuated valve to deliver a greater amount of process fluid, the magnitude of the control signal applied to the electro-pneumatic controller associated with the valve may increase (e.g., from 10 milliamps (mA) to 15mA where the electro-pneumatic actuator is configured to receive a 4-20mA control signal).

Electro-pneumatic actuators typically include a pneumatic module, which may include a first pneumatic stage (e.g., a current-to-pressure (I/P) transducer or a voltage-to-pressure (E/P) transducer) and a second pneumatic stage (e.g., a relay). The pneumatic module typically receives a pressurized supply fluid, such as air, and adjusts the pressurized supply fluid in accordance with a control signal (e.g., a current drive signal) to generate a pneumatic output signal in response to the control signal. The supply fluid is typically provided to the electro-pneumatic controller, and more specifically, to the pneumatic stage of the electro-pneumatic controller, via a supply pressure regulator (such as a filtered pressure reducer (airset) device or an air filter device) located between the pressure source and the pressure supply input of the electro-pneumatic device. Pressure regulators are typically configured to provide an appropriate supply pressure to ensure that the control pressure output of the electro-pneumatic controller does not exceed a certain maximum pressure (e.g., a maximum control pressure rating of an actuator being controlled by the electro-pneumatic controller), thereby providing overpressure protection for the device being controlled.

However, a malfunction or failure of a pressure regulator may cause an overpressure in the device controlled by the electro-pneumatic controller, which may damage the device being controlled (e.g., rupture an actuator) and may result in a potentially dangerous situation in the process control system. To protect the device in the event of a failure or malfunction of the pressure regulator, a relief valve is typically coupled between a control pressure output of the electro-pneumatic controller and a control pressure input of the device controlled by the controller. The relief valve, for example, vents the control fluid to the atmosphere when the pressure of the control fluid rises, for example, due to a failure or malfunction of the pressure regulator device. In this way, the relief valve provides redundant over-pressure protection for the plant to avoid over-pressurization of the plant in the event of a failure or malfunction of the supply fluid regulator plant. However, such safety valves can be very expensive and inconvenient and/or can be difficult to install into process control equipment.

Disclosure of Invention

According to a first exemplary aspect, a method for limiting a control pressure provided to an actuator of a valve coupled to a valve positioner is provided. The method includes providing a drive signal to a pneumatic stage of the valve positioner, wherein the pneumatic stage is configured to control an output pressure of the valve positioner based on the drive signal. The method also includes obtaining a pressure measurement from a pressure sensor communicatively coupled to the valve positioner and detecting an abnormal pressure based on the pressure measurement. The method also includes controlling the drive signal to limit the output pressure of the valve positioner in response to detecting the abnormal pressure, wherein the output pressure provides a control pressure to the actuator.

According to a second exemplary aspect, a process control device includes a valve; an actuator coupled to the valve and configured to control a position of the valve; and a valve positioner coupled to the valve and the actuator, the valve positioner configured to provide a control pressure to the actuator to control a position of the actuator. The valve positioner includes a pneumatic stage configured to receive a drive signal and control an output pressure of the valve positioner based on the drive signal. The valve positioner also includes an over-voltage protection module configured to: obtaining a measurement from a pressure sensor communicatively coupled to the valve positioner; detecting an abnormal pressure based on the pressure measurement; and in response to detecting the abnormal pressure, controlling the drive signal to limit an output pressure of the valve positioner, wherein the output pressure provides the control pressure to the actuator.

According to a third exemplary aspect, a valve positioner coupled to a process control device including a valve and an actuator is configured to receive a control signal from a process control system and control a pressure provided to the actuator based on the control signal. The valve positioner includes a pneumatic stage configured to receive a drive signal and control an output pressure of the valve positioner based on the drive signal. The over-pressure protection module further comprises an over-pressure protection module configured to obtain a measurement from a pressure sensor communicatively coupled to the valve positioner; detecting an abnormal pressure based on the pressure measurement; and in response to detecting the abnormal pressure, controlling the drive signal to limit an output pressure of the valve positioner, wherein the output pressure provides a control pressure to the actuator.

A method, process control device and/or valve positioner according to any one or more of the first, second or third aspects described above may also include any one or more of the following preferred forms.

In a preferred form, the pressure sensor is configured to sense a level of supply pressure provided to the valve positioner.

In another preferred form, the pressure sensor is configured to sense a level of the output pressure of the valve positioner.

In another preferred form, detecting the abnormal pressure includes: comparing the pressure measurement to a predetermined threshold; and determining that the pressure is abnormal when the measured pressure exceeds the predetermined threshold.

In another preferred form, the valve positioner includes a processor and a memory, and detecting the abnormal pressure and controlling the drive signal includes executing computer readable instructions stored in the memory.

In another preferred form, the valve positioner includes a control circuit configured to receive the pressure measurement, and the detecting the abnormal pressure and controlling the drive signal are performed by the control circuit.

In another preferred form, the drive signal is a current signal and controlling the drive signal includes setting the drive signal to a value of zero milliamps or near zero milliamps.

In another preferred form, the drive signal is a voltage signal and controlling the drive signal includes setting the drive signal to a value of zero millivolts or close to zero millivolts.

In another preferred form, the overpressure protection module is configured to compare the pressure measurement to a predetermined threshold; and determining that the pressure is abnormal when the measured pressure exceeds the predetermined threshold.

In another preferred form, the valve positioner includes a processor and a memory, and the overpressure protection module includes computer readable instructions stored in the memory and executable by the processor.

In another preferred form, the overvoltage protection module includes hardware control circuitry.

In another preferred form, the drive signal is a current drive signal and the overpressure detection module is configured to set the drive signal to a value of zero milliamps or near zero milliamps in response to detecting the abnormal pressure.

In another preferred form, the drive signal is a voltage drive signal, and wherein the over-voltage detection module is configured to set the drive signal to a value of zero millivolts or near zero millivolts in response to detecting the abnormal pressure.

Drawings

FIG. 1 is a schematic representation of a process control system having one or more field devices configured in accordance with the principles of the present invention.

FIG. 2 is a block diagram of an example field device configured in accordance with an embodiment of the invention.

FIG. 3 is a block diagram of an exemplary field device configured in accordance with another embodiment of the invention.

Fig. 4 is a flow diagram of an overvoltage protection scheme in accordance with one embodiment.

FIG. 5 is a block diagram of an exemplary field device configured in accordance with another embodiment of the invention.

FIG. 6 is a block diagram of an exemplary field device configured in accordance with yet another embodiment of the present invention.

FIG. 7 is a flow chart of an example method for limiting a control pressure provided to an actuator of a valve coupled to a valve positioner.

Detailed Description

Referring now to FIG. 1, a process control system 10 constructed in accordance with one version of the present invention is shown to include one or

more field devices

15, 16, 17, 18, 19, 20, 21, 22 and 71 in communication with a process controller 11, which in turn communicates with a data historian 12 and one or more user workstations 13, each of the user workstations 13 having a display screen 14. So configured, the controller 11 transmits signals to and receives signals from the

field devices

15, 16, 17, 18, 19, 20, 21, 22, and 71 and the workstation 13 to control the process control system.

In more detail, the process controller 11 of the version of the process control system 10 shown in FIG. 1 is connected via hardwired communication connections to the

field devices

15, 16, 17, 18, 19, 20, 21 and 22 via input/output (I/O)

cards

26 and 28. The data historian 12 may be any desired type of data collection unit having any type of memory for storing data and any desired or known software, hardware, or firmware. Further, although the data historian 12 is shown in FIG. 1 as a separate device, it may alternatively or additionally be part of one of the workstations 13 or another computer device (e.g., a server). The controller 11 may be, for example, DeltaV sold by Emerson Process management^TMA controller communicatively connected to the workstation 13 and the data historian 12 via a communication network 29, the communication network 29 may be, for example, an Ethernet connection.

As described above, the controller 11 is illustrated as communicatively coupled to the

field devices

15, 16, 17, 18, 19, 20, 21, and 22 using a hardwired communication scheme that may include using any desired hardware, software, and/or firmware to implement hardwired communication, including standard 4-20mA communication and/or using any intelligent communication protocol (e.g., such as

A field bus communication protocol,

Communication protocol, etc.). The

field devices

15, 16, 17, 18, 19, 20, 21, and 22 may be any type of device such as sensors, control valve assemblies, transmitters, positioners, etc., while the I/

O cards

26 and 28 may be any type of I/O device conforming to any desired communication or controller protocol. In the embodiment shown in FIG. 1, the

field devices

15, 16, 17, 18 are standard 4-20mA devices that communicate over analog lines to an I/O card 26, while the

digital field devices

19, 20, 21, 22 may be smart devices, such as

Communication devices and fieldbus field devices that communicate with the I/O card 28 over a data bus using fieldbus protocol communications. Of course, the

field devices

15, 16, 17, 18, 19, 20, 21, and 22 may conform to any other desired standard or protocol, including any standard or protocol developed in the future.

Further, the process control system 10 shown in FIG. 1 includes a plurality of

wireless field devices

60, 61, 62, 63, 64, and 71 disposed within the plant to be controlled. The

field devices

60, 61, 62, 63, 64 are shown as transmitters (e.g., process variable sensors), while the field device 71 is shown as a control valve assembly, including, for example, control valves and actuators. Wireless communication may be established between the controller 11 and the

field devices

60, 61, 62, 63, 64, and 71 using any desired wireless communication device, including currently known or later developed hardware, software, firmware, or any combination thereof. In the version shown in fig. 1, an antenna 65 is coupled to transmitter 60 dedicated to performing wireless communications for transmitter 60, while a wireless router or other module 66 having an antenna 67 is coupled for centrally processing wireless communications for

transmitters

61, 62, 63, and 64. Similarly, an antenna 72 is coupled to the control valve assembly 71 for performing wireless communication for the control valve assembly 71. The field devices or associated

hardware

60, 61, 62, 63, 64, 66 and 71 may implement protocol stack operations used by appropriate wireless communication protocols to receive, decode, route, encode and transmit wireless signals via the

antennas

65, 67 and 72 to implement wireless communication between the process controller 11 and the

transmitters

60, 61, 62, 63, 64 and the control valve assembly 71.

If desired, the

transmitters

60, 61, 62, 63, 64 may constitute a single link between the various process sensors (transmitters) and the process controller 11 so that they can be relied upon to send accurate signals to the controller 11 to ensure that process performance is not compromised. The

transmitters

60, 61, 62, 63, 64 are commonly referred to as Process Variable Transmitters (PVTs) and may therefore play an important role in the control of the overall control process. In addition, control valve assembly 71 may provide measurements derived from sensors within control valve assembly 71, or as part of its operation, may provide other data generated or calculated by control valve assembly 71 to controller 11. Of course, it is well known that the control valve assembly 71 may also receive control signals from the controller 11 to affect physical parameters, such as flow, throughout the process.

The process controller 11 is coupled to one or more I/

O devices

73 and 74, each I/

O device

73 and 74 is connected to a respective antenna 75 and 76, and these I/O devices and

antennas

73, 74, 75, 76 operate as transmitters/receivers to perform wireless communications with the

wireless field devices

61, 62, 63, 64 and 71 via one or more wireless communication networks. Wireless communication between field devices (e.g.,

transmitters

60, 61, 62, 63, 64 and control valve assembly 71) may use one or more known wireless communication protocols, such as

Protocol, Ember protocol, WiFi protocol, IEEE wireless standard, etc. Further, the I/

O devices

73 and 74 may implement protocol stack operations used by these communication protocols to receive, decode, route, encode, and transmit wireless signals via the antennas 75 and 76 to enable wireless communication between the controller 11 and the

transmitters

60, 61, 62, 63, 64 and the control valve assembly 71.

As shown in FIG. 1, the controller 11 generally includes a processor 77 that implements or monitors one or more process control routines (or any modules, blocks or subroutines) stored in a memory 78. The process control routines stored in the memory 78 may include or be associated with control loops implemented in a process plant. In general, and as is generally known, the process controller 11 executes one or more control routines and communicates with the

field devices

15, 16, 17, 18, 19, 20, 21, 22, 60, 61, 62, 63, 64, and 71, the user workstation 13, and the data historian 12 to control a process in any desired manner.

FIG. 2 is a block diagram of an example field device 200 configured in accordance with an embodiment of the invention. The field device 200 may be integrated within a process control system, such as the example process control system 100 of FIG. 1. Referring to FIG. 1, the field device 200 may be, for example, one of the field devices 15-18 that communicates with the controller 11 over an analog connection using standard 4-20mA communications. In another embodiment, the field device 200 may be one of the field devices 19-22 that communicates with the controller 11 over a digital bus using a digital communication protocol (such as the HART or Fieldbus protocol or any other suitable digital communication protocol). In yet another embodiment, the field device 200 may be a field device 72 that communicates with the controller 11 via a wireless connection using any suitable wireless communication protocol. In this embodiment, field device 200 includes an antenna (not shown) that is included in field device 200 or coupled to field device 200 to enable wireless communication between field device 200 and controller 11.

The field device 200 is illustrated in fig. 2 as a control valve assembly having a valve 202, an actuator 204, and a valve positioner 206 communicatively coupled to the valve 202 and the actuator 204. The valve 202 may be, for example, a rotary valve, a quarter turn valve, a damper, or any other control device or apparatus. The actuator 204 may be a pneumatic actuator that is operatively coupled to a flow control element within the valve 202, for example, via a valve stem. The valve stem may move the flow control element in a first direction (e.g., away from the valve seat) to allow fluid flow between the inlet and the outlet, and may move the flow control element in a second direction (e.g., toward the valve seat) to restrict or prevent fluid flow between the inlet and the outlet. In various embodiments, the actuator 204 may include a double-acting piston actuator, a single-acting spring return diaphragm (piston actuator), or a piston actuator, or any other suitable actuator or process control device.

In FIG. 2, the valve positioner 206 is shown as a digital valve positioner having a processor 208, a memory 210, and an interface module 212. In addition, the valve positioner 206 includes a pneumatic module 214 having a first pneumatic stage 215 and a second pneumatic stage 216. The first pneumatic stage 215 may be an electropneumatic transducer, such as a current-to-pressure (I/P) transducer, a voltage-to-pressure (E/P) transducer, or the like, which may produce an output pressure proportional to a drive signal provided to the first pneumatic stage 215. The second pneumatic stage 216 may be operable to amplify the pressure generated by the first pneumatic stage 215 to generate a pressure suitable for operation of the actuator 204. The second pneumatic stage 216 may be, for example, a spool valve, a poppet valve, a relay, or the like. The network interface 212 of the valve positioner 206 is configured to transmit and/or receive signals according to a particular communication protocol of the process control system to which the field device 200 belongs. In some embodiments, the communication protocol is a wireless mesh network protocol, such as the WirelessHART or isa100.11a protocol. Alternatively, the network interface 212 may support wired communications, such as standard 4-20mA communications, and/or use any intelligent communication protocol (e.g., USB, etc.)

A field bus communication protocol,

Communication protocol, etc.). In some embodiments, the network interface 212 includes a transceiver (not shown). The transceiver typically includes one or more processors (also not shown) for executing instructions related to Physical (PHY) layer and other layer (e.g., Media Access Control (MAC) layer) tasks in accordance with a wireless communication protocol used by the process control system. The network interface may be coupled to one or more antennas (not shown). Via the one orThe plurality of antennas, network interface 212, transmits and/or receives data packets according to a wireless communication protocol. The network interface 212 is preferably configured to both send and receive data packets.

The processor 208 may be a general purpose processor, a digital signal processor, an ASIC, a field programmable gate array, or any other known or future developed processor. The processor 208 operates according to instructions stored in the memory 210. Although the example field device 200 of fig. 2 includes one processor 208, other embodiments may include two or more processors that perform the functions of the processor 208. The memory 210 may be volatile memory or non-volatile memory. Memory 210 may include one or more of Read Only Memory (ROM), Random Access Memory (RAM), flash memory, Electrically Erasable Programmable Read Only Memory (EEPROM), or other types of memory. The memory 210 may comprise an optical, magnetic (hard drive) or any other form of data storage device.

In operation, the processor 208 receives a command signal, such as a 4 to 20mA command signal or a 0 to 10V command signal, representative of a desired position of the valve 202. The processor 208 also receives an indication of the actual position of the valve 202 provided to the processor 208 by the stroke sensor 218. The travel sensor 218 may be an analog travel sensor and may be coupled to the processor 208 via an analog-to-digital converter 219. An analog-to-digital converter 219 may convert the analog signal generated by the travel sensor 218 to a digital signal suitable for use by the processor 208. In another embodiment, the travel sensor 218 may be a digital sensor. For example, the travel sensor 218 may include an analog-to-digital converter internal to the travel sensor 218. In this case, the analog-to-digital converter 219 may be omitted, and the output of the travel sensor 218 may be provided directly to the processor 208.

The processor 208 compares the desired position of the valve 202 indicated by the command signal received from the process controller to the actual position of the valve 202 indicated by the travel sensor 218 and generates a drive signal for the pneumatic module 214 based on the difference between the desired position and the actual position of the valve 202. The drive signal may be, for example, a current drive signal or a voltage drive signal. The drive signal corresponds to an amount by which the valve positioner 206 is to change the position of the actuator 204 coupled to the valve 202. The drive signal generated by the processor 208 is provided to the first pneumatic stage 215 of the pneumatic module 214 via a digital-to-analog converter 217, the digital-to-analog converter 217 converting the (digital) drive signal generated by the processor 208 into an analog drive signal suitable for driving the first pneumatic stage 215. The first pneumatic stage 215 adjusts the pressurized supply fluid provided to the first pneumatic stage 215 in accordance with the drive signal to produce an output pressure proportional to the drive signal. The output pressure of the first pneumatic stage 215 is provided to the second pneumatic stage 216, and the second pneumatic stage 216 may amplify the pressure output of the first pneumatic stage 215 and may provide the amplified pressure to the pressure output of the valve positioner 206. A pressure output of the valve positioner 206 is coupled to a control pressure input of the actuator 204 and provides a control pressure for the actuator 204 to control a position of the actuator 204 to control the valve 202 to move toward a desired position of the valve 202.

It should be noted that although the first pneumatic stage 215 is generally described herein as a proportional I/P transducer, the first pneumatic stage 215 may also be an on/off transducer. In this case, the pneumatic module 214 may alternate between providing pressurized supply fluid and releasing the pressurized supply fluid (e.g., into the atmosphere) to the control pressure input of the actuator 204 to control the position of the actuator 204. It should also be noted that the valve positioner 206 may include other types of position control mechanisms instead of, or in addition to, that shown in FIG. 2. Further, it should be understood that field device 200 may be any other type of pneumatically controlled device operating within a process control system. For example, field device 200 can be a damper or the like.

With continued reference to fig. 2, the supply pressure may be provided to the valve positioner 206, and more specifically, to the first pneumatic stage 215 and the second pneumatic stage 216, via a pressure regulator (e.g., a filter reducer 220). The filter reducer 220 may condition and filter a pressurized supply fluid (e.g., air) provided by a pressure supply source in the process control system and may reduce the pressure provided by the pressure supply source to a pressure level suitable for use by the valve positioner 206 and the actuator 204. In general, the valve positioner 206 generates an output pressure by adjusting the supply pressure, and the generated output pressure is typically pressurized at a level that is lower than the supply pressure. In some cases, the valve positioner 206 may output all of the supply pressure provided to the valve positioner 206 to the actuator 204 to provide a maximum force to the actuator 204, e.g., to force the valve 202 into a valve seat. By regulating and/or reducing the pressure provided by the pressure supply, the pressure regulator 220 generally ensures that the output control pressure of the valve positioner 206 does not exceed a certain maximum level, such as a maximum pressure rating of the actuator 204, thereby providing overpressure protection for the actuator 204. However, in the event of a malfunction or failure of the filter pressure reducer 220 (e.g., when the filter pressure reducer 220 is normally open and thus provides full supply pressure instead of reduced supply pressure to the valve positioner 206), the valve positioner 206 may produce a pressure output that exceeds a maximum rated value of the actuator 204 or other desired maximum control pressure level of the actuator 204, such as in the event that the valve positioner 206 outputs the full supply pressure of the valve positioner 206 to the actuator 204, thereby exceeding the maximum control pressure of the actuator 204. Exceeding the maximum pressure of the actuator 204 may over-pressurize the actuator 204, which may damage the actuator 204 and/or may result in a potentially dangerous condition in the process control system.

The valve positioner 206 includes an overpressure protection module 222 and a pressure sensor 224. The overpressure protection module 222 generally ensures that a safe control pressure is provided to the actuator 204 even in the event of a failure or malfunction of the filter pressure reducer 220, thereby providing additional or redundant overpressure protection for the actuator 204. In the embodiment of fig. 2, overvoltage protection module 222 includes computer readable instructions stored in memory 210. The processor 208 is configured to execute the computer readable instructions to provide overvoltage protection for the actuator 204. The overpressure protection module 222 may operate to limit the drive signal provided to the first pneumatic stage 215 to ensure that the pressure output of the valve positioner 206 does not exceed a certain maximum value, such as a maximum pressure rating of the actuator 204, or any other suitable value required or desired for operation of the actuator 204.

The pressure sensor 224 is coupled to the output pressure of the valve positioner 206 and is configured to provide a measurement of the output pressure of the valve positioner 206 to the processor 208. The pressure sensor 224 may be an analog pressure sensor, in which case the output of the pressure sensor 224 may be coupled to an analog-to-digital converter 225. An analog-to-digital converter 225 may convert the analog signal generated by the pressure sensor 224 to a digital signal suitable for use by the processor 208. In another embodiment, pressure sensor 224 may be a digital pressure sensor. For example, the pressure sensor 224 may include an analog-to-digital converter internal to the pressure sensor 224. In this case, the analog-to-digital converter 225 may be omitted and the output of the pressure sensor 224 may be provided directly to the processor 208.

The over-pressure protection module 222 may monitor the pressure output of the valve positioner 206 by periodically taking pressure measurements provided by the pressure sensor 224. The overpressure protection module 222 may compare a measurement obtained from the pressure sensor 224 to a predetermined threshold and may detect an abnormal (e.g., abnormally high) pressure when the measured pressure exceeds the predetermined threshold. In response to detecting the abnormal pressure, the over-pressure protection module 222 may control a level of a drive signal provided by the processor 208 to the first pneumatic stage 215 to limit the output pressure of the first pneumatic stage 215 and, thus, the valve positioner 206. For example, the overvoltage protection module 222 can set the drive signal to a predetermined value, such as a value of zero milliamps or near zero milliamps (in the case where the drive signal is a current drive signal) or a value of zero millivolts or near zero millivolts (in the case where the drive signal is a voltage drive signal). Alternatively, the over-pressure protection module 222 may set the drive signal to another suitable value, or may adjust the drive signal in another suitable manner, thereby reducing or limiting the pressure output of the valve positioner 206.

As yet another example, in response to detecting an abnormal pressure, the over-pressure protection module 222 may operate to prevent any further adjustment of the drive signal to stop any further adjustment of the output pressure level of the valve positioner 206. In this case, the output pressure level of the valve positioner 206 will cease to respond to further changes in the command signal received by the valve positioner 206. In this way, the output pressure of the valve positioner 206 will remain at the level produced by the valve positioner 206 until an abnormal pressure is detected, such as, in this embodiment, a malfunction or failure of the filter pressure reducer 220. Alternatively, in response to detecting an abnormal pressure, the over-pressure protection module 222 may operate to prevent any further increase in the level of the drive signal while still allowing the level of the drive signal to decrease in response to receiving a command signal that causes the level of the drive signal to decrease. In either case, the over-pressure protection module 222 operates to ensure that the output pressure level does not increase to a level that would render operation of the actuator 204 unsafe and/or undesirable in response to detecting the abnormal pressure.

The components of the valve positioner 206 may be communicatively coupled as shown in fig. 2 or may be coupled in any other suitable manner. Further, the valve positioner 206 may include any other components for controlling and/or providing pressure to the actuator 204 in addition to or in place of the components shown in FIG. 2. Additionally or alternatively, although not shown, the valve positioner 206 may include other signal processing components, such as analog-to-digital converters, digital-to-analog converters, filters (low pass, high pass, and digital), amplifiers, and so forth.

Fig. 3 is a block diagram of a field device 200 configured in accordance with another embodiment of the invention. In the embodiment of FIG. 3, valve positioner 206 of FIG. 2 is replaced with valve positioner 306. Valve positioner 306 is generally similar to valve positioner 206 and includes a number of similarly numbered elements as valve positioner 206. However, valve positioner 306 is configured to detect an abnormal supply pressure provided to valve positioner 306 rather than an abnormal output pressure as is detected by valve positioner 206.

Valve positioner 306 includes an overpressure protection module 322 and a pressure sensor 324. Pressure sensor 324 is coupled to a supply pressure of valve positioner 306 and is configured to measure a level of the supply pressure provided to valve positioner 306. The pressure sensor 324 may provide the supply pressure measurement to the processor 208. The pressure sensor 324 may be an analog pressure sensor, in which case the output of the pressure sensor 324 may be coupled to an analog-to-digital converter 325. The analog-to-digital converter 325 may convert the analog signal generated by the pressure sensor 324 to a digital signal suitable for use by the processor 208. Alternatively, pressure sensor 324 may be a digital pressure sensor. For example, the pressure sensor 324 may include an analog-to-digital converter internal to the pressure sensor 324. In this case, analog-to-digital converter 325 may be omitted from valve positioner 306, and the output of pressure sensor 324 may be provided directly to processor 208.

The overvoltage protection module 322 comprises computer readable instructions stored in the memory 210 and executable by the processor 208. The overvoltage protection module 322 can be the same as or similar to the overvoltage protection module 222 of fig. 2. The overpressure protection module 322 may operate in the same or similar manner as the overpressure protection module 222 to detect an abnormal pressure and, in response to detecting the abnormal pressure, control the level of the drive signal provided to the first pneumatic stage 215 to limit the output pressure of the valve positioner 306. However, in the embodiment of FIG. 3, the overpressure module 322 operates by detecting an abnormal pressure based on a supply pressure measurement provided by the pressure sensor 324. For example, the over-pressure protection module 322 may obtain a measurement of the supply pressure from the pressure sensor 324 and may compare the obtained supply pressure measurement to a predetermined threshold. The over-pressure protection module 322 may detect an abnormal pressure when the supply pressure measurement exceeds a predetermined threshold. In response to detecting the abnormal pressure, the overpressure protection module 322 may control the level of the drive signal provided to the first pneumatic stage 215. For example, the overvoltage protection module 322 may set the drive signal to zero milliamps, set the drive signal to zero millivolts, set the drive signal to another appropriate value, prevent further adjustment of the drive signal, prevent further increase of the drive signal, and so on, as described above with reference to the overvoltage protection module 222 of fig. 2.

Fig. 4 is a flow diagram of an overvoltage protection scheme 400 that can be implemented by the overvoltage protection module 222 of fig. 2 or the overvoltage protection module 322 of fig. 3. Referring to fig. 2 and 3, the over-pressure protection module 222 or the over-pressure protection module 322 may operate according to a scheme 400 to control the drive signal provided to the first pneumatic stage 215 to limit the output pressure of the valve positioner 206. At block 402, the over-pressure protection module obtains measurements from a pressure sensor, such as a pressure sensor coupled to an output of a valve positioner or a pressure sensor coupled to a supply pressure of the valve positioner. At block 404, the over-pressure protection module compares the pressure measurement obtained at block 402 to a predetermined threshold. If the measured pressure exceeds the predetermined threshold, the scheme 400 continues at block 406, where the over-pressure protection module controls a drive signal provided to a pneumatic stage of the valve positioner to reduce an output pressure of the valve positioner. For example, the over-voltage protection module sets the drive signal to a value of zero milliamps or near zero milliamps, sets the drive signal to a value of zero millivolts or near zero millivolts, or sets the drive signal to any other suitable value. Alternatively, the overvoltage protection module can prevent further adjustment of the drive signal, thereby locking the drive signal at the current value of the drive signal. In another example, the over-pressure protection module may prevent further increases in the drive signal while still allowing the drive signal to decrease, or may control the drive signal in another suitable manner to limit the output pressure level of the valve positioner. In either case, the scheme 400 then returns to block 402, where the processor obtains the next measurement from the pressure sensor.

Returning to block 404, if the comparison of block 404 indicates that the measured pressure does not exceed (e.g., is less than or equal to) the predetermined threshold, the scheme 400 simply returns to block 402 to obtain the next measurement from the pressure sensor.

Fig. 5 is a block diagram of a field device 200 configured in accordance with another embodiment of the invention. In the embodiment of FIG. 4, the valve positioner 206 (FIG. 2) is replaced with a valve positioner 506. The valve positioner 506 is generally similar to the valve positioner 206 of FIG. 2 and includes many similarly numbered elements as the valve positioner 206 of FIG. 2. In the embodiment of FIG. 5, overpressure protection is provided by a hardware module, such as a control circuit, coupled to the first pneumatic stage 215 and configured to control a drive signal provided to the first pneumatic stage 215 to limit the output pressure of the valve positioner 506 in response to detecting an abnormal output pressure of the valve positioner 506.

The valve positioner 506 includes an overpressure protection module 522 coupled between the processor 208 and the pneumatic module 214. The pressure sensor 524 is coupled to the output pressure of the valve positioner 506 and is configured to measure a level of the output pressure of the valve positioner 506. The pressure sensor 524 provides an output pressure measurement to the overpressure protection module 522. The over-pressure protection module 522 may include analog circuitry and/or digital circuitry configured to detect an abnormal output pressure of the valve positioner 506 based on an output pressure measurement provided by the pressure sensor 524. The pressure sensor 524 may be coupled to an analog-to-digital converter, if necessary, or to a digital-to-analog converter to generate a signal suitable for use by the overpressure protection module 522.

In response to detecting an abnormal pressure based on measurements obtained from the pressure sensor 524, the over-pressure protection module 522 operates to affect the level of the drive signal provided to the pneumatic stage 215 to limit the pressure output of the valve positioner 506. For example, the overvoltage protection module 522 may set the drive signal to a level of zero milliamps or near zero milliamps or a level of zero millivolts or near zero millivolts (turn off the drive signal), set the drive signal to another appropriate value, prevent further adjustment of the drive signal, prevent further increase of the drive signal, and so on, in response to detecting the abnormal pressure, as described above with reference to the overvoltage protection module 222 of fig. 2.

Fig. 6 is a block diagram of a field device 200 configured in accordance with another embodiment of the invention. In the embodiment of FIG. 6, the valve positioner 206 (FIG. 2) is replaced with a valve positioner 606. The valve positioner 606 is generally similar to the valve positioner 506 of FIG. 5 and includes many like-numbered elements to the valve positioner 506 of FIG. 5. In the embodiment of FIG. 6, overpressure protection is provided by a hardware module, such as a control circuit, coupled to the first pneumatic stage 215 and configured to control a drive signal provided to the first pneumatic stage 215 to limit the output pressure of the valve positioner 606 in response to detecting an abnormal supply pressure of the valve positioner 606.

The valve positioner 606 includes an overpressure protection module 622 coupled between the processor 208 and the pneumatic stage 214. A pressure sensor 624 is coupled to a supply pressure of the valve positioner 606 and to an overpressure protection module 624. Pressure sensor 624 is configured to measure a level of supply pressure of valve positioner 606 and provide the supply pressure measurement to overpressure protection module 622. Overpressure protection module 622 may include analog circuitry and/or digital circuitry configured to detect abnormal pressures based on supply pressure measurements obtained from pressure sensor 624. The pressure sensor 624 can be coupled to an analog-to-digital converter, if necessary, or to a digital-to-analog converter to generate a signal suitable for use by the over-pressure protection module 622.

In response to detecting an abnormal pressure based on measurements obtained from pressure sensor 624, overpressure protection module 622 controls the level of the drive signal provided to pneumatic stage 215, thereby limiting the pressure output of valve positioner 606. For example, the overvoltage protection module 622 can set the drive signal to a level of zero milliamps or near zero milliamps or a level of zero millivolts or near zero millivolts (turn off the drive signal), set the drive signal to another appropriate value, prevent further adjustment of the drive signal, prevent further increase of the drive signal, and so forth in response to detecting the abnormal pressure, as described above with reference to the overvoltage protection module 222 of fig. 2.

Referring to fig. 5 and 6, although the

valve positioners

506 and 606 are shown as digital valve positioners, the

valve positioners

506 and 606 may instead be analog valve positioners configured to receive analog command signals, such as 4-20mA command signals, and control the position of the valve 202 in accordance with the analog command signals. In some such embodiments, the interface 212 and/or the processor 208 and the memory 210 may be omitted from the

valve positioners

506, 606. In this case, the analog command signal may be provided to the pneumatic stage 214 via the

overpressure protection modules

522, 622 to provide overpressure protection for the actuator 204.

In various embodiments described above, the

overpressure protection modules

222, 322, 522, 622 may be configured to cause a signal indicative of an abnormal pressure (e.g., a supply input abnormal pressure or a control pressure output abnormal pressure) to be sent to a controller and/or a host device in a process control system to which the field device 200 belongs, such as to the process controller 11 of FIG. 1, in response to detecting the abnormal pressure. Sending a signal indicative of the detected abnormal pressure to a controller or host device in the process control system may indicate to an operator monitoring the process control system that filter reducer 220 is malfunctioning, and may allow the operator to take appropriate action, such as repairing or replacing the filter reducer, shutting down field device 200, shutting down the process control system (or a portion thereof) that includes field device 200, and so forth.

FIG. 7 is a flow chart of an example method 700 for limiting a control pressure provided to an actuator of a valve coupled to a valve positioner. In various embodiments, the method 700 is implemented by the field device 200 of FIG. 2. In one embodiment, the method 700 is implemented by the processor 208 in accordance with the overvoltage protection module 222 stored in the memory 210. In another embodiment, method 700 is implemented using a hardware over-voltage protection module coupled to a current drive input of a pneumatic stage of a valve positioner. In other embodiments, method 700 is implemented at least in part using other components of field device 200, or by a device other than field device 200.

At block 702, a pressure measurement is obtained. In one embodiment, the pressure measurement is obtained from a pressure sensor coupled to a control pressure output of the valve positioner. In another embodiment, the pressure measurement is obtained from a pressure sensor coupled to a supply pressure input of the valve positioner. At block 704, an abnormal pressure is detected based on the pressure measurement obtained at block 702. For example, the pressure measurement is compared to a predetermined threshold and an abnormal pressure is detected when the pressure measurement obtained at block 702 exceeds the predetermined threshold. Then, at block 706, in response to detecting the abnormal pressure at block 704, a drive signal provided to a pneumatic stage of the valve positioner is controlled to limit an output control pressure of the valve positioner. For example, block 706 may include setting the drive signal to zero milliamps, setting the drive signal to zero millivolts, setting the drive signal to another appropriate value, preventing the drive signal from further adjustment, preventing the drive signal from further increase, and so forth, as described above in various embodiments.

Although various functions and/or systems of a field device have been described herein as "modules," "components," or "functional blocks," it should be noted that these terms are not limited to a single, integrated unit. Furthermore, while the present invention has been described with reference to specific examples, those examples are illustrative only and are not intended to be limiting of the invention. It will be apparent to those skilled in the art that changes, additions or deletions may be made to the disclosed embodiments without departing from the spirit and scope of the invention. For example, one or more portions of the methods described above can be performed in a different order (or simultaneously) and still achieve desirable results.

Claims

1. A method for limiting a control pressure provided to an actuator of a valve coupled to a valve positioner, the method comprising:

providing a drive signal to a pneumatic stage of the valve positioner, wherein the pneumatic stage is configured to control an output pressure of the valve positioner as a function of the drive signal;

obtaining a pressure measurement from a pressure sensor communicatively coupled to the valve positioner;

detecting an abnormal pressure based on the pressure measurement; and

in response to detecting the abnormal pressure, controlling the drive signal to limit the output pressure of the valve positioner, wherein the output pressure provides a control pressure to the actuator.

2. The method of claim 1, wherein the pressure sensor is configured to sense a level of supply pressure provided to the valve positioner.

3. The method of claim 1, wherein the pressure sensor is configured to sense a level of the output pressure of the valve positioner.

4. The method of claim 1, wherein detecting the abnormal pressure comprises:

comparing the pressure measurement to a predetermined threshold; and is

Determining the pressure as abnormal when the measured pressure exceeds the predetermined threshold.

5. The method of claim 1, wherein the valve positioner comprises a processor and a memory, and wherein detecting the abnormal pressure and controlling the drive signal comprises executing computer readable instructions stored in the memory.

6. The method of claim 1, wherein the valve positioner includes control circuitry configured to receive the pressure measurement, and wherein detecting the abnormal pressure and controlling the drive signal are performed by the control circuitry.

7. The method of claim 1, wherein the drive signal is a current signal, and wherein controlling the drive signal comprises setting the drive signal to a value of zero milliamps or near zero milliamps.

8. The method of claim 1, wherein the drive signal is a voltage signal, and wherein controlling the drive signal comprises setting the drive signal to a value of zero millivolts or near zero millivolts.

9. A process control device, comprising:

a valve;

an actuator coupled to the valve and configured to control a position of the valve; and

a valve positioner coupled to the valve and the actuator, the valve positioner configured to provide a control pressure to the actuator to control a position of the actuator, the valve positioner comprising:

a pneumatic stage configured to receive a drive signal and control an output pressure of the valve positioner as a function of the drive signal, an

An overvoltage protection module configured to:

obtaining a measurement from a pressure sensor communicatively coupled to the valve positioner;

detecting an abnormal pressure based on the pressure measurement; and

in response to detecting the abnormal pressure, controlling the drive signal to limit an output pressure of the valve positioner, wherein the output pressure provides the control pressure to the actuator.

10. The process control device of claim 9, wherein the pressure sensor is configured to measure a level of supply pressure provided to the valve positioner.

11. The process control device of claim 9, wherein the pressure sensor is configured to measure a level of pressure output by the valve positioner.

12. The process control device of claim 9, wherein the overvoltage protection module is configured to:

comparing the pressure measurement to a predetermined threshold; and is

13. The process control device of claim 9, wherein the valve positioner comprises a processor and a memory, and wherein the over-pressure protection module comprises computer readable instructions stored in the memory and executable by the processor.

14. The process control device of claim 9, wherein the drive signal is a current drive signal, and wherein the overpressure detection module is configured to set the drive signal to a value of zero milliamps or near zero milliamps in response to detecting the abnormal pressure.

15. The process control device of claim 9, wherein the drive signal is a voltage drive signal, and wherein the over-voltage detection module is configured to set the drive signal to a value of zero millivolts or near zero millivolts in response to detecting the abnormal pressure.

16. A valve positioner coupled to a process control device including a valve and an actuator, the valve positioner configured to receive a control signal from a process control system and control a pressure provided to the actuator in accordance with the control signal, the valve positioner comprising:

An overvoltage protection module configured to:

detecting an abnormal pressure based on the pressure measurement; and

in response to detecting the abnormal pressure, controlling the drive signal to limit an output pressure of the valve positioner, wherein the output pressure provides a control pressure to the actuator.

17. The valve positioner of claim 16, wherein the pressure sensor is configured to measure a level of supply pressure provided to the valve positioner.

18. The valve positioner of claim 16, wherein the pressure sensor is configured to measure a level of pressure output by the valve positioner.

19. The valve positioner of claim 16, wherein the valve positioner comprises a processor and a memory, and the overpressure protection module comprises computer readable instructions stored in the memory and executable by the processor.

20. The valve positioner of claim 16, wherein the drive signal is a current drive signal, and wherein the overpressure detection module is configured to set the drive signal to a value of zero milliamps or near zero milliamps in response to detecting the abnormal pressure.

21. The valve positioner of claim 16, wherein the drive signal is a voltage drive signal, and wherein the overpressure detection module is configured to set the drive signal to a value of zero millivolts or near zero millivolts in response to detecting the abnormal pressure.