Field device switch monitoring

Abstract

The invention relates to field device switch monitoring. An industrial process field device is disclosed that includes an active component, a switch, a switch monitor, and a controller. The active component can be a sensor configured to sense a process parameter, or a control device configured to control a process of an industrial process. The switch is electrically coupled to a first terminal and a second terminal. The switch monitor is configured to detect an open state or a closed state of the switch and generate a first state output, a second state output, or a dither state output. A dithering prevention circuit outputs a dithering stable state output based on the dither state output. The controller is configured to set the switch to the open state or the closed state and generate a notification based on any of the first state output and the second state output and the dithering stable state output, the notification indicating at least one of a current state and a condition of the switch.

Description

Technical Field

[0001] Embodiments of this disclosure relate to industrial process control systems. More specifically, embodiments of this disclosure relate to an industrial process field device having a switch monitor for monitoring the state of a switch on a field device. Background Technology

[0002] In industrial environments, control systems are used to monitor and control inventory and other aspects of industrial and chemical processes. Typically, control systems utilize industrial process field devices distributed at critical locations within the industrial process and connected to control circuitry via process control loops to perform these functions. The term "field device" refers to any device performing a function in a distributed control or process monitoring system, including all currently known or yet-to-be-understood devices used in the measurement, control, and / or monitoring of industrial processes.

[0003] Typical field devices include device circuitry that enables them to perform routine field device tasks, such as process parameter monitoring and measurement using one or more sensors, and / or process control operations using one or more control devices. Exemplary sensors include pressure sensors, level sensors, temperature sensors, and other sensors used in industrial processes. Exemplary control devices include actuators, solenoids, valves, and other control devices.

[0004] The device circuitry of the field device may also include a controller for controlling sensors and / or control equipment, and for communicating with a process control system or other circuitry via, for example, a process control loop (such as a 4mA-20mA process control loop). In some installations, the process control loop is used to deliver regulated current and / or voltage to the field device to power it. The process control loop may also carry data, such as process parameter values ​​corresponding to the sensed process parameters. This data may be transmitted via the process control loop as an analog signal or as a digital signal. Summary of the Invention

[0005] This disclosure relates to field devices for industrial processes, industrial process control systems, and methods for controlling external devices using industrial process field devices. One embodiment of the field device includes an active component, a switch, a switch monitor, and a controller. The active component may be a sensor configured to sense process parameters or a control device configured to control an industrial process. Preferably, the switch is electrically connected to a first terminal and a second terminal, and is configured to electrically connect the first and second terminals when in a closed state, and to disconnect the first and second terminals when in an open state. The switch monitor is configured to detect the current state of the switch corresponding to a closed or open state, and generate a status output indicating the current state. The status output is a first status output indicating the open state of the switch when the switch is in the open state, a second status output indicating the closed state of the switch when the switch is in the closed state and connected to DC power, and a jitter status output indicating the closed state of the switch when the switch is in the closed state and connected to AC power. The anti-jitter circuit of the switch monitor is configured to output a jitter-stable status output with a stable DC voltage based on the jitter status output. The controller is configured to set the switch to an open or closed state and generate a notification based on any one of a first state output, a second state output, and a jitter-stable state output, which indicates the current state of the switch and / or the condition of the switch.

[0006] One embodiment of the industrial process control system includes the aforementioned field devices, external devices, and a power supply. The external devices are electrically connected to the switch via a first terminal. The power supply is electrically connected to the switch via a second terminal and is configured to supply power to the external devices through the switch. When the switch is closed, power is supplied to the external devices, and when the switch is open, power is disconnected from the external devices.

[0007] In one embodiment of the method, process parameters of an industrial process are sensed, or the industrial process is controlled using active components of a field device. A switch drive signal generated by the field device's controller sets the switch of the field device to a current state corresponding to an open or closed state, wherein in the open state, power from an external power source is disconnected from the external device, and in the closed state, power from an external power source is connected to the external device. A switch monitor of the field device is used to detect electrical parameters indicating the current state of the switch. The switch monitor generates a state output indicating the current state based on the detected electrical parameters. The state output is a first state output indicating the open state of the switch when it is in the open state, a second state output indicating the closed state of the switch when it is in the closed state and the power source includes DC, and a jitter state output indicating the closed state of the switch when it is in the closed state and the power source includes AC. Using the switch monitor's anti-jitter circuitry, a jitter-stable state output with a stable DC voltage is generated based on the jitter state output indicating the closed state of the switch. The controller generates a notification based on any one of the first state output, the second state output, and the jitter-stable state output, indicating the current state of the switch and / or the conditions of the switch.

[0008] This summary provides a simplified overview of some concepts, which are further described in the detailed embodiments below. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to help determine the scope of the claimed subject matter. Attached Figure Description

[0009] Figure 1 and Figure 2 This is a simplified diagram of an exemplary process control system according to an embodiment of the present disclosure.

[0010] Figure 3 This is a simplified block diagram of a switch monitor 140 according to an embodiment of the present disclosure.

[0011] Figure 4 and Figure 5 This is a circuit diagram of an exemplary switch monitor for an industrial process field device according to an embodiment of this disclosure.

[0012] Figure 6 A graph of the AC voltage of a switch delivered to a field device according to an embodiment of the present disclosure is shown, as well as a graph of the status output generated by an exemplary switch monitor of an industrial process field device.

[0013] Figure 7 and Figure 8 This illustrates an embodiment of the present disclosure where, when the monitored switch is powered by a 20VDC power supply and a 250VAC power supply respectively, the switch control signal and... Figure 3 A graph illustrating the relationship between the status outputs of a switch monitor and time.

[0014] Figure 9 This is a simplified circuit diagram of a switch monitoring circuit including a jitter reduction circuit according to an embodiment of this disclosure.

[0015] Figure 10 This is a simplified circuit diagram of an example of a de-jitter circuit according to an embodiment of the present disclosure.

[0016] Figure 11 It is the truth table of a D-type flip-flop.

[0017] Figure 12 yes Figure 10 Truth table for the anti-jitter circuit.

[0018] Figure 13 Includes a series of diagrams illustrating simulated examples of the operation of the switch monitor and the debounce circuit.

[0019] Figure 14 This is a flowchart illustrating a method for controlling external devices using industrial process field equipment according to an embodiment of this disclosure. Detailed Implementation

[0020] Embodiments of this disclosure are described more fully below with reference to the accompanying drawings. Elements identified by the same or similar reference numerals are the same or similar elements. However, various embodiments of this disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and that they will fully convey the scope of this disclosure to those skilled in the art.

[0021] The embodiments disclosed herein relate to industrial process field devices, industrial process control systems including field devices, and methods for controlling external devices using field devices. Figure 1 and Figure 2 This is a simplified diagram of an exemplary process measurement or control system 100 according to an embodiment of this disclosure.

[0022] System 100 includes an industrial process field device 102 that can interact with industrial process 104. In some embodiments, process 104 involves, for example, materials, such as fluids, processed by system 100, which pass through pipes (such as pipe 105). Figure 1 The transportation and / or containment of materials in tanks. This type of material handling typically transforms materials from a lower-value state into higher-value and more useful products, such as petroleum, chemicals, paper, and food. For example, oil refineries perform industrial processes that can process crude oil into gasoline, fuel oil, and other petrochemical products.

[0023] Field device 102 can communicate with computer control unit 106, which can be configured to control field device 102. Control unit 106 can be located remotely from the field device, such as in the control room of system 100. Figure 1 As shown.

[0024] Control unit 106 can be communicatively connected to field device 102 via a suitable physical or wireless communication link. For example, the control unit can be connected to the field device via control loop 107. Communication between control unit 106 and field device 102 can be performed on control loop 107 according to conventional analog and / or digital communication protocols. In some embodiments, process control loop 107 includes a 4 mA-20 mA process control loop, wherein the process variable can be determined by the loop current I flowing through process control loop 107. Figure 2 The level representation of the signal. Exemplary digital communication technologies include digital signals modulated onto the analog current level of the two-wire process control loop 107, such as the HART® communication standard. Other purely digital technologies may also be used, including FieldBus and Profibus communication protocols. The control unit 106 may include a power supply that powers the field device 102 via the control loop 107.

[0025] In some implementations, the field device 100 includes a controller 108, one or more active components in the form of sensors or control devices 110, measurement or control circuitry 112, a digital-to-analog converter (DAC) 114, communication circuitry 115, and / or a junction box 116, such as... Figure 2 A simplified diagram is shown. Controller 108 may represent one or more processors (e.g., microprocessors, central processing units, etc.) that control components of field device 100 to perform one or more functions described herein in response to the execution of instructions, which may be locally stored in a non-transitory patent-compliant computer-readable medium or memory 118 of device 100. In some embodiments, the processor of controller 108 is a component of one or more computer-based systems. In some embodiments, controller 108 includes one or more control circuits, a microprocessor-based system, or one or more programmable hardware components, such as field-programmable gate arrays (FPGAs), for controlling components of device 100 to perform one or more functions described herein. Controller 108 may also represent other conventional field device circuitry.

[0026] Use by Figure 2Box 110 in the diagram represents one or more sensors that field device 102 can use to sense or measure parameters of process 104, such as temperature, level, pressure, flow rate, or another parameter of process 104. Exemplary sensors 110 include pressure sensors, temperature sensors, level sensors, flow rate sensors, and / or other sensors for sensing or measuring process parameters.

[0027] Field device 100 can also be configured to use by Figure 2 Box 110 in the diagram represents one or more control devices for controlling aspects of process 104. Exemplary control devices 110 include actuators, solenoids, valves, and other conventional process control devices used in field equipment to control the process.

[0028] Measurement or control circuitry 112 represents circuitry that interacts with sensor or control device 110. For example, circuitry 112 may include measurement circuitry that converts the output from sensor 110 for use by controller 108 of a field device. For instance, by adjusting loop current I to indicate the value of a process parameter sensed by sensor 110, controller 108 may use DAC 114 to convert a digital signal into an analog signal, which is then transmitted to control unit 106 via communication circuitry 115, such as through a two-wire process control loop 107. Circuitry 112 may also be used to control control device 110, such as in response to commands from control unit 106 or other locations, received by controller 108 via communication circuitry 115.

[0029] Embodiments of this disclosure relate to a field device 102 including a switch 120. The switch 120 may be electrically connected, for example, via a junction box 116 to a power source 124 and a device 126, which are external to the field device 102. Therefore, embodiments of the power source 124 and device 126 are isolated from the field device 102. A controller 108 controls the switch 120 to electrically connect or disconnect power from the power source 124 to the device 126. Exemplary embodiments of the device 126 include, for example, a pump, compressor, solenoid, or another device suitable for use with the system 100.

[0030] Switch 120 may take any suitable form. For example, switch 120 may include a latching relay or another suitable switch. In addition, although only a single switch 120 is shown, it should be understood that field device 102 may include multiple switches 120, which may be coupled to, for example, junction box 116 and each controlled by controller 108.

[0031] In some embodiments, the controller 108 selectively sets (i.e., controls, actuates, or toggles) the switch 120 between a closed state and an open state, in which the switch 120 connects the device 126 to power from the power source 124, and in which the switch 120 disconnects the device 126 from the power source 124. Therefore, the device 126 can be activated during or in response to the switch 120 being set to the closed state, and deactivated in response to the switch 120 being set to the open state. In some embodiments, the state of the switch 120 is set in response to a switch drive or control signal 128 from the controller 108.

[0032] In some implementations, controller 108 is configured to set switch 120 to an open or closed state in response to instructions executed by the processor based on one or more settings. Setting and programming instructions may be stored in memory 118 as the memory of settings 130, control unit 106, and / or stored in another suitable location. Settings 130 may include user-defined settings such as thresholds and / or other switch control parameters.

[0033] In one implementation, controller 108 sets switch 120 to an open or closed state in response to a sensed parameter (e.g., pressure, level, flow rate, temperature, etc.) detected by sensor 110. For example, controller 108 may compare the sensed parameter value output from circuit 112 based on the parameter output from sensor 110 with a setting 130 such as a user-defined threshold, and use drive signal 128 to set switch 120 to a predetermined open or closed state when the sensed parameter value meets a predetermined relationship with the threshold.

[0034] Alternatively, control unit 106 may receive sensed parameter values ​​from field device 102, and when the sensed parameter values ​​satisfy a predetermined relationship with setting 130, such as a user-defined threshold, it may issue a command to controller 108 via control loop 107 to set switch 120 to the desired state. Controller 108 then generates drive signal 128 to set switch 120 to the desired state in response to the command from control unit 106.

[0035] In one example, field device 102 may include a level sensor 110 that senses the liquid level in the tank and transmits the sensed level to control unit 106 using communication circuitry 115. When the level output indication generated by sensor 110 drops below a threshold (e.g., setting 130) of the sensed liquid level, controller 108 may be configured or commanded by control unit 106 to close switch 120 to start an external pump (device 126) and drive additional material into the tank. After the liquid level sensed by sensor 110 reaches another threshold level (setting 130), such as a level indicating that the tank is full, controller 108 may be configured or commanded to open switch 120 and deactivate the pump.

[0036] In another embodiment, controller 108 uses switch drive signal 128 to set switch 120 to an open or closed state in response to the state of control device 110. Alternatively, control unit 106 may command controller 108 to set switch 120 to an open or closed state based on the state of control device 110. Here, control device 110 includes at least two distinct states, such as the open or closed state of a valve, the position of an actuator or solenoid, or another state of control device 110. For example, when control device 110 is a valve and device 126 is a pump, controller 108 may be configured or commanded to set switch 120 to a closed state when the valve is open to start the pump and drive material flow through the valve, and controller 108 may be configured or commanded to set switch 120 to an open state when the valve is closed to deactivate the pump.

[0037] It is important that switch 120 operates correctly by achieving the intended open or closed state. An undetected failure of switch 120 to enter the desired state set by controller 108 can lead to numerous problems, including safety issues, regulatory issues, process quality issues, and other potential problems that could result in plant shutdowns and lengthy troubleshooting and repair procedures. For example, if controller 108 sends a drive signal 128 to switch 120 from the closed state to the open state to deactivate the pump (device 126) filling the tank with fluid, but switch 120 fails to switch to the open state, the pump can continue to operate, potentially leading to fluid overflow from the tank and other potentially problematic consequences. Such switch failures typically require immediate attention to mitigate potential damage. Unfortunately, providing sufficient manual oversight of field devices 102 within an industrial system to identify faulty or malfunctioning switches 120 is often too time-consuming and costly.

[0038] According to the implementation of the field device 102 of this disclosure, a switch monitor 140 is included. Figure 2This switch monitor 140 can be used to verify that switch 120 of field device 102 is operating as expected. Switch monitor 140 can be electrically connected to power supply 124 and device 126 via, for example, junction box 116. Figure 2 As shown. In some embodiments, the switch monitor 140 is configured to handle power supply 124, which provides direct current (DC) or DC voltage, such as 20-60VDC, or alternating current (AC) or AC voltage, such as 20-250VAC.

[0039] In some implementations, switch monitor 140 is configured to detect (e.g., sense or measure) the current state of switch 120 (i.e., open or closed) and generate a status output 142 indicating the current state of switch 120. Controller 108 is configured to generate a notification 144 based on the status output 142. For example, the notification 144 can be transmitted to control unit 106 or another location using communication circuitry 115, via a wired (e.g., control loop 107) or wireless communication link.

[0040] Implementations of notification 144 indicate the current state of switch 120, and / or whether switch 120 is operating correctly (i.e., the condition of switch 120). Notification 144 may take any suitable form. Exemplary notification 144 includes or triggers: an alarm (audible and / or visual); a status report presented on a display, such as on the display of control unit 106; analog or digital communication or messaging via a wireless or wired communication link, such as communication or settings transmitted through process control loop 107; or another notification. For example, notification 144 may be transmitted using communication circuit 115 by setting the loop current I to a predetermined level or one of a plurality of predetermined levels, each of the plurality of predetermined levels indicating a different notification.

[0041] In some implementations, controller 108 generates notification 144 based on a comparison between status output 142 and the expected state of the switch corresponding to switch drive signal 128, which sets the state of switch 120 based on sensed parameters, commands, and / or the state of control devices, as discussed above. This comparison can be performed using comparator circuitry 146, which compares status output 142 and switch drive signal 128 and outputs signal 148 based on the comparison. Signal 148 can indicate the correspondence between switch drive signal 128 and status output 142, such as when switch drive signal 128 is configured to set switch 120 to the open state and status output 142 indicates that switch 120 is in the open state. In this case, it is assumed that switch 120 is operating correctly. Alternatively, signal 148 can indicate a conflict between switch drive signal 128 and status output 142, such as when switch drive signal 128 is configured to set switch 120 to the open state and status output 142 indicates that switch 120 is in the closed state. In this scenario, it is assumed that switch 120 is operating incorrectly. Notification 144 can be generated by controller 108 in response to signal 148 to indicate whether switch 120 is operating correctly or incorrectly. Additionally, notification 144 can indicate the current state of switch 120 as indicated by switch output 142, and / or the expected state of switch 120 corresponding to switch drive signal 128.

[0042] In some implementations, controller 108 generates notification 144 based on a comparison between status output 142 and switch setting 150, which may be stored in memory 118, for example... Figure 2 As shown. Switch setting 150 indicates the expected or desired open or closed state of switch 120. Therefore, switch setting 150 typically corresponds to switch drive signal 128 that sets the state of switch 120, and can be based on sensed parameters, the state of the control device, and / or commands, as discussed above. Controller 108 determines whether there is a correspondence between switch setting 150 and state output 142 (indicating that switch 120 is operating correctly) or a conflict between switch setting 150 and state output 142 (indicating that switch 120 is operating incorrectly). Notification 144 is generated by controller 108 to indicate the correct or incorrect operation of switch 120. Additionally, notification 144 can indicate the current state of switch 120 as indicated by switch output 142, and / or the expected state of switch 120 as indicated by switch setting 150.

[0043] In some embodiments, the switch monitor 140 includes circuitry that detects (i.e., senses or measures) an electrical parameter indicating the current state (i.e., open or closed) of the switch 120, and generates a state output 142 based on the detected electrical parameter. Embodiments of the electrical parameter include the voltage (AC or DC) across the switch 120, the current (AC or DC) through the switch 120, or another suitable electrical parameter. In some embodiments, the switch monitor 140 generates the state output 142 based on the detected electrical parameter indicating the current state of the switch 120.

[0044] In some implementations, the state output 142 corresponds to two distinct voltage values: a fixed or stable logic or digital low voltage representing a digital 0 value, and a fixed or stable logic or digital high voltage representing a digital 1 value. One of these values ​​can be used to indicate the open state of switch 120, while the other value is used to indicate the closed state of switch 120. This selection may depend on the application (e.g., normally open switch application versus normally closed switch application). For the purposes of this disclosure, a logic low voltage or digital 0 value will be used to indicate the open state of switch 120, and a logic high voltage or digital 1 value will indicate the closed state of switch 120.

[0045] Figure 3 This is a simplified block diagram of a switch monitor 140 according to an embodiment of the present disclosure. In one embodiment, the switch monitor 140 includes circuitry forming a differential amplifier 151 and a comparator 152. The differential amplifier is connected to terminals 153 and 154 of the switch 120 (these terminals may be terminals of the junction box 116 connected to the power supply 124 and corresponding to the load of the attached device 126), as... Figure 2 As shown, a differential voltage 155 is generated based on the voltage difference across terminals 153 and 154 or the current through switch 120. The comparator typically compares the output from the differential amplifier with a reference voltage and generates a status output 142 based on this comparison.

[0046] Figure 4 and Figure 5 This is a circuit diagram of exemplary switch monitors 140A and 140B according to embodiments of this disclosure. Exemplary switch monitor 140A is configured to generate a status output 142 based on the voltage (AC or DC) across switch 120, and exemplary switch monitor 140B is configured to generate a status output 142 based on the current I flowing through switch 120. S A status output 142 (i.e., an analog voltage) is generated (AC or DC). Switch monitors 140A and 140B are respectively connected to terminals 153 and 154. Power supply 124 is typically represented by an AC or DC voltage source 156 and a resistor 158 connected to terminal 153. Device 126 is electrically connected to terminal 154 and voltage source 156 or electrical ground / common terminal.

[0047] In some embodiments, the differential amplifier 151 of the switch monitor 140A includes a voltage rectifier 160 that allows the switch monitor 140A to operate during the negative period of an AC waveform supplied by power supply 124. In one exemplary embodiment, the rectifier 160 includes a diode 162 and a capacitor 164. The diode 162 blocks the negative period portion of the AC waveform generated by power supply 124. The capacitor 164 charges during the positive period of the AC waveform and slowly decays during the negative period of the AC waveform, while the diode 162 is blocking the waveform. The capacitor 164 is appropriately sized to substantially maintain the voltage charge acquired during the positive period of the AC waveform during the negative period.

[0048] Differential amplifier 151 may include resistors 166, 168, 170, and 172, and an operational amplifier (op-amp) 174 having a positive power supply input coupled to a power supply voltage Vs and a negative power supply input coupled to electrical ground 175. The ratio of resistors 166 and 170, and resistors 168 and 172, sets the gain of operational amplifier 174 to detect the voltage difference across switch 120 and between terminals 153 and 154, which is indicated by differential voltage output 155. Resistors 166, 168, 170, and 172 have relatively high resistance to reduce larger AC / DC sensed voltages to levels within the operating range of the lower voltage state monitoring circuitry.

[0049] The comparator 152 of the switch monitor 140A may include an operational amplifier 178 having a positive power supply input coupled to a power supply voltage Vs and a negative power supply input coupled to electrical ground 175. The operational amplifier 178 compares the voltage difference across switch 120, indicated by a differential voltage output 155, with a threshold voltage, and outputs a state output 142 based on this comparison. This threshold voltage is set by a voltage divider formed by resistors 180 and 182. The threshold voltage can be adjusted to correctly trigger within the voltage range switched by switch 120. For example, additional circuitry, such as that described below, may be used to process output 142 or isolate output 142 before processing by the microprocessor of controller 108.

[0050] Figure 6 Two graphs are shown, which compare the AC voltage delivered from power source 124 to switch 120 with the voltage delivered by power source 124 to switch 120. Figure 4The example switch monitor 140A generates a state output 142 for comparison. During the time period t0-t1, switch 120 is in the open state, and the voltage across switch 120 reflects the AC voltage supplied by power supply 124. For this example, switch monitor 140A generates a logic low state output 142 for the open state of switch 120. At time t1, switch 120 closes. This causes current to flow through switch 120 and to device 126. Additionally, the voltage across switch 120 drops substantially to near zero. This change in voltage across switch 120 causes switch monitor 140A to generate a logic high state output 142.

[0051] Example switch monitor 140B ( Figure 5 It is configured to be based on the current I passing through switch 120 S (AC or DC) Generates a status output 142. Switch 140B includes a differential amplifier 151 connected to terminals 153 and 154, which may be, for example, terminals of junction box 116, such as... Figure 2 As shown. The differential amplifier 151 of the switch monitor 140B may include a voltage rectifier 160 of circuit 140A formed by diode 162 and capacitor 164, which operates as described above.

[0052] The differential amplifier of the switch monitor 140B may include resistors 186, 188, 190, and 192, and an operational amplifier 194 having a positive power supply input connected to the supply voltage Vs and a negative power supply input connected to electrical ground 195. The ratio of resistors 186 and 190 and resistors 188 and 192 sets the gain of the operational amplifier 194 to detect the voltage difference across resistor 196, which is connected in series with switch 120. Resistors 186, 188, 190, and 192 have relatively high resistance to reduce large AC / DC sensed voltages to levels within the operating range of the lower voltage state monitoring circuitry. Operational amplifier 194 responds to current I... S The voltage difference signal 198 is output based on the voltage across resistor 196.

[0053] The signal 198 from the operational amplifier 194 of the differential amplifier 151 is an analog voltage proportional to the current through resistor 196. Using the known value of resistor 196 and the analog voltage of the state output 142, comparator 152 can process signal 198 and compare it with a reference, producing a corresponding state output 142 that can be processed by controller 108. For example, additional circuitry can be used to process output 142 or isolate output 142 before it is processed by the microprocessor of controller 108. Controller 108 can also operate as comparator 152, processing signal 198 from differential amplifier 151 based on the value of resistor 196 and determining the current I. SThen the current I can be... S The settings are compared to determine whether switch 102 (e.g., normally open or normally closed switch) is in the open or closed state.

[0054] The implementation of the switch monitor 140 described above operates to provide a single sense-level status output 142 for a wide range of input voltages from power supply 124, such as DC voltages of 20-60VDC and AC voltages of 20-250VAC. Because the threshold of comparator 152 must be set low enough to sense the possible range of voltages across switch 120 (e.g., across terminals 153 and 154) (e.g., 20-60VDC), the switch monitor 140 may be susceptible to noise and AC connection issues. This can cause the digital output of status output 142 to jitter (i.e., continuously switching between high and low states) instead of the expected fixed high output when switch 120 is closed (no voltage across the switch).

[0055] Reference Figure 7 and Figure 8 The two figures illustrate an example of a situation that generates a jittery output 142. They show the switch control signal 128 when switch 120 is powered by a 20VDC power supply 124 and a 250VAC power supply 124, respectively. Figure 2 A graph showing the relationship between the switch control signal 128 and the state output 142 over time. When the switch control signal 128 changes the state of the 20VDC-powered switch 120 from open to closed at time t0, there is no longer a voltage difference across the switch 120, thus generating a high logic voltage (digital 1) state output 142 at time t1. Figure 7 As shown.

[0056] However, when switch 120 is powered by a 250VAC power supply 124, and the switch control signal 128 changes the state of switch 120 from open to closed at time t0, due to noise (e.g., EMC, AC connection from adjacent switches or power supplies, etc.), the state output jitters between low and high logic voltages starting at time t1, such as... Figure 8 As shown. In the event of such jitter in the status output 142, there is a possibility that the controller 108 will detect an incorrect reading of the status of switch 120 and issue an incorrect notification 144 of switch failure. Such an incorrect diagnostic notification 144 can have serious consequences, such as process shutdown, wasted time and money investigating the fault notification, and reduced confidence in the performance of field device 102.

[0057] In some implementations, the switch monitor 140 includes anti-jitter circuitry that operates to stabilize the jittered state output 142 under closed switch and certain AC voltage power conditions, while typically transmitting or reproducing the state output 142 under other power and state conditions of the switch 120.

[0058] This modification is usually in Figure 9 The simplified circuit diagram is shown. The anti-jitter circuit 200 receives the state output 142 and generates a stable state output 142' in response. Here, the differential amplifier 151 and comparator 152 are essentially as described above. Figures 3-6 It operates as described and generates a state output 142 based on the sensed conditions. A stable state output 142' is then used instead. Figure 2 The status output 142 is used by the controller 108 to determine the current state of the switch 120 and to generate a notification 144 as described above.

[0059] When switch 120 is in the open state, when switch 120 is connected to a 20-60VDC power supply 124, or in another scenario where no jittering state output 142 is generated, the stable state output 142' generated by the debounce circuit 200 typically reflects the output of state output 142. That is, when state output 142 is a fixed or stable logic low or logic high voltage signal, the stable state output essentially reflects the state output. However, when switch 120 is closed and connected to 20-250VAC (such as 250VAC) and state output 142 is jittering, the stable state output 142' generated by the debounce circuit 200 corresponds to the expected logic voltage output (e.g., a fixed high logic voltage) of the expected correct state signal 142 of the closed state of switch 120. Therefore, the debounce circuit 200 corrects the aforementioned deficiency and reduces the likelihood that field device 102 will issue a fault diagnosis notification 144.

[0060] The anti-shake circuit 200 can take many forms. One example of circuit 200 is... Figure 10 The simplified diagram shows the use of a D-type flip-flop 204. Figure 11 This is the truth table of a D-type flip-flop 204.

[0061] like Figure 10 As shown, the D input of flip-flop 204 is pulled to a digital high voltage (V). DDThe clock pin (CLK) of flip-flop 204 is driven by the state output 142 from switch monitor 140. The clear pin (CLR) of flip-flop 204 is used to reset the output of circuit 200 using switch control signal 128. This allows the Q output of flip-flop 204 to remain high when it sees a rising edge on state output 142, and since the steady-state output 142' is read by controller 108 after each state change, a pulse will clear the Q output to logic or digital low voltage before each measurement.

[0062] During operation, when controller 108 issues a status control signal 128 (e.g., a voltage pulse) to change the state of switch 120, the status control signal 128 will also clear the Q output of the flip-flop 204 because the flip-flop 204 is connected to the CLR input. In one embodiment, at startup, an initial reset switch control signal 128 is generated to ensure a known state output 142.

[0063] Since the D input is pulled to logic high, the Q output will remain low or transition to high based on the presence of a rising edge on the CLK input driven by the status output 142. Figure 12 The truth value shown indicates that the state output 142 (CLK input) jitters due to the closed state condition of switch 120 and the AC power to terminals 153 and 154 of the switch. Figure 8 In the case of ), the Q output will go high and remain high, thereby eliminating jitter and generating the desired logic high voltage to indicate the closed state of switch 120.

[0064] In some implementations, after the controller 108 sends a switch control signal or pulse 128, it briefly waits to allow the switch monitor 140 and the anti-jitter circuit 200 to stabilize before measuring the steady-state output 142'.

[0065] In some implementations, the debounce circuit includes an OR gate 206 that receives the Q output from flip-flop 204 and a status output 142, and operates to prevent erroneous tripping for conditions under which switch 120 is initially closed. For example, when power is supplied to switch 120 and switch 120 is initially in the closed state, status output 142 would be a logic high voltage. However, during initial startup, switch control signal 128 can clear the Q output to a logic low voltage, and since there is never a rising edge on the clock input (CLK), Q will remain at a logic low voltage, but it should be a logic high voltage to indicate that switch 120 is closed. By feeding the Q output and status output 142 into OR gate 206, this condition is resolved, and the eventually stable status output 142' will remain high during this startup cycle, thus indicating the correct state of switch 120.

[0066] Figure 13The simulation includes a series of graphs illustrating examples of the operation of the switch monitor 140 and the anti-jitter circuit 200 when power supply 124 provides AC power to terminals 153 and 154 of switch 120 connected to a load or device 126. Parasitic capacitance and AC noise are added to the simulation to trigger thresholds during switch closure.

[0067] First, the controller 108 generates a switch control signal or pulse 128 to change the switch 120 from the open state to the closed state. This closing of the switch is indicated by the current diagram through the switch 120.

[0068] As shown in the diagram, these events cause the status output 142 from the switch monitor 140 to jitter. However, the anti-jitter circuit 200 eliminates the jitter of the status output 142, resulting in a fixed, stable status output 142'. Shortly after the controller 128 generates another switch control signal or pulse 128, the switch 120 is turned on, and both the status output 142 and the stable status output 142' transition to a logic low voltage.

[0069] Additional embodiments of this disclosure relate to a method of controlling an external device 126 using an industrial process field device 102 formed according to one or more embodiments described herein. Figure 14 This is a flowchart illustrating one implementation of the method.

[0070] At point 210 of the method, process parameters of industrial process 104 are sensed, or process 104 is controlled using active components 110 of field device 102. Thus, the active component may be a sensor that senses process parameters, or a control device that controls the process, as discussed above.

[0071] At 212, the switch 120 of field device 102 is set to a current state corresponding to an open or closed state, in which power from external power source 124 is disconnected from external device 126, and in which power from external power source 124 is connected to external device 126. In some embodiments, switch 120 is set to the current state in response to a switch control signal 128 generated by controller 108 of field device 102, as discussed above.

[0072] At 214, the switch monitor 140 of the field device 102 is used to detect (i.e., sense or measure) electrical parameters indicating the current state of switch 120. As discussed above, implementations of the electrical parameters include the voltage (AC or DC) across switch 120 and the current (AC or DC) through switch 120.

[0073] At 216, a switch monitor 140 generates a status output 142 indicating the current state based on the detected electrical parameters. The status output 142 is a first status output (such as logic low voltage) indicating the open state of switch 120 when switch 120 is in the open state, a second status output (such as logic high voltage) indicating the closed state of switch 120 when switch 120 is in the closed state and the power supplied by power supply 124 includes DC power, and a jitter status output indicating the closed state of switch 120 when switch 120 is in the closed state and the power includes AC power.

[0074] At 218, based on the jitter state output indicating the closed state of switch 120, the jitter stable state output 142' with a stable DC voltage is generated by the anti-jitter circuit 200 of switch monitor 140.

[0075] At 220, controller 108 generates a notification based on any one of the first state output, the second state output, and the jitter-stabilized state output. Each of these state outputs can be generated by anti-jitter circuit 200 based on state output 142. As discussed above, notification 144 can indicate the current state of switch 120, and / or whether switch 120 is operating correctly.

[0076] Although embodiments of the present disclosure have been described with reference to preferred embodiments, those skilled in the art will recognize that changes in form and detail may be made without departing from the spirit and scope of the present disclosure.

Claims

1. A field device for an industrial process, comprising: an active component selected from a sensor configured to sense a process parameter, and a control device configured to control the industrial process; a switch electrically coupled to a first terminal and a second terminal, and configured to electrically connect the first terminal and the second terminal when in a closed state, and to electrically disconnect the first terminal and the second terminal when in an open state; a switch monitor configured to generate a state output based on an electrical parameter of the switch, the state output being a first state output indicative of the open state of the switch when the switch is in the open state, a second state output indicative of the closed state of the switch when the switch is in the closed state, and a dithered state output indicative of the closed state of the switch when the switch is in the closed state, the dithered state output comprising a signal alternating between the first state output and the second state output due to noise introduced to the switch monitor; a dithering prevention circuit of the switch monitor configured to output a dithering stabilized state output having a stable DC voltage based on the dithered state output indicative of the closed state of the switch; and a controller configured to set the switch to one of the open state and the closed state, and to generate a notification based on any of the first state output, the second state output, and the dithering stabilized state output, the notification being indicative of at least one of a current state of the switch and a condition of the switch.

2. The field device of claim 1, wherein: one of the first state output and the second state output comprises a logic low voltage; the other of the first state output and the second state output comprises a logic high voltage; and the dithered state signal comprises a voltage alternating between the logic low voltage and the logic high voltage.

3. The field device of claim 2, wherein the switch monitor comprises: a differential amplifier configured to output a differential voltage based on a voltage difference between the first terminal and the second terminal of the switch or a current through the switch; and a comparator configured to output one of the first state output, the second state output, and the dithered state signal based on the differential voltage.

4. The field device of claim 3, wherein the dithering prevention circuit is configured to output a first stabilized state output substantially mirroring the first state output based on the first state output, and a second stabilized state output substantially mirroring the second state output based on the second state output.

5. The field device of claim 4, wherein: the controller sets the switch to the open state or the closed state using a switch control signal; ​ ​ The anti-jitter circuit includes a D-type flip-flop having a clear (CLR) input that receives the switch control signal, a clock (CLK) input that receives the state output, and a D input that receives a logic high voltage; and The anti-jitter circuit includes a D-type flip-flop having a clear (CLR) input that receives the switch control signal, a clock (CLK) input that receives the state output, and a D input that receives a logic high voltage; and 6. The field device of claim 5, wherein the anti-jitter circuit includes an OR gate connected to the Q output and the state output.

7. The field device of claim 4, wherein the controller generates the notification based on a comparison of any of the first stable state output, the second stable state output, and the jitter stable state output to a switch setting indicative of an expected state of the switch.

8. The field device of claim 4, wherein: the controller is configured to set the switch to the open state or the closed state using a switch control signal; and the controller generates the notification based on a comparison of any of the first stable state output, the second stable state output, and the jitter stable state output to the switch control signal.

9. The field device of claim 1, wherein: the controller is configured to set the switch to the open state or the closed state using a switch control signal; the active component includes the sensor having a parameter output corresponding to a sensed process parameter; and the controller is configured to set the switch to one of the open state and the closed state based on the parameter output using the switch control signal.

10. The field device of claim 9, wherein: the sensor is selected from the group consisting of a pressure sensor, a level sensor, a flow sensor, and a temperature sensor; the device includes a measurement circuit configured to generate a parameter value based on the parameter output; and the controller is configured to communicate the parameter value and the notification to a remote location using a communication circuit.

11. The field device of claim 1, wherein: the controller is configured to set the switch to the open state or the closed state using a switch control signal; the active component includes the control device selected from the group consisting of an actuator, a valve, and a solenoid; the control device includes at least two different states; and the controller is configured to set the switch to one of the open state and the closed state based on the state of the control device using the switch control signal.

12. An industrial process control system comprising: a field device including: an active component selected from a sensor configured to sense a process parameter, and a control device configured to control the industrial process; a controller configured to generate a notification based on a comparison of any of a first stable state output, a second stable state output, and a jitter stable state output to a switch setting indicative of an expected state of a switch. a switch electrically coupled to the first terminal and the second terminal and configured to electrically connect the first terminal and the second terminal when in a closed state and to electrically disconnect the first terminal and the second terminal when in an open state; a switch monitor configured to generate a state output based on an electrical parameter of the switch, the state output being a first state output indicative of the open state of the switch when the switch is in the open state, a second state output indicative of the closed state of the switch when the switch is in the closed state, and a dithered state output indicative of the closed state of the switch when the switch is in the closed state, the dithered state output comprising a signal alternating between the first state output and the second state output due to noise introduced to the switch monitor; a dithering prevention circuit of the switch monitor configured to output a dithering stabilized state output having a stable DC voltage based on the dithered state output indicative of the closed state of the switch; and a controller configured to set the switch to one of the open state and the closed state and to generate a notification based on any one of the first state output, the second state output, and the dithering stabilized state output, the notification being indicative of at least one of a current state of the switch and a condition of the switch, an external device electrically coupled to the switch through the first terminal; and a power source electrically coupled to the switch through the second terminal and configured to power the external device through the switch; wherein power is supplied to the external device when the switch is in the closed state and power is disconnected from the external device when the switch is in the open state.

13. The system of claim 12, wherein: one of the first state output and the second state output comprises a logical low voltage; the other of the first state output and the second state output comprises a logical high voltage; and the dithered state signal comprises a voltage alternating between the logical low voltage and the logical high voltage.

14. The system of claim 13, wherein the switch monitor comprises: a differential amplifier configured to output a differential voltage based on a voltage difference between the first terminal and the second terminal of the switch or a current through the switch; and a comparator configured to output one of the first state output, the second state output, and the dithered state signal based on the differential voltage.

15. The system of claim 14, wherein the dithering prevention circuit is configured to output a first stabilized state output substantially mirroring the first state output based on the first state output and a second stabilized state output substantially mirroring the second state output based on the second state output.

16. The system of claim 15, wherein: the controller uses a switch control signal to set the switch to the open state or the closed state; the anti-jitter circuit includes a D-type flip-flop having a clear (CLR) input that receives the switch control signal, a clock (CLK) input that receives the state output, and a D input that receives a logic high voltage; and the anti-jitter circuit generates the jitter-stable state output, the first stable state output, and the second stable state output based on the state output at a Q output of the flip-flop.

17. The system of claim 16, wherein the anti-jitter circuit includes an OR gate connected to the Q output and the state output.

18. The system of claim 15, wherein the controller generates the notification based on a comparison of any of the first stable state output, the second stable state output, and the jitter-stable state output to a switch setting that indicates an expected state of the switch.

19. The system of claim 15, wherein: the controller is configured to use a switch control signal to set the switch to the open state or the closed state; and the controller generates the notification based on a comparison of any of the first stable state output, the second stable state output, and the jitter-stable state output to the switch control signal.

20. A method of controlling an external device using an industrial process field device, comprising: sensing a process parameter of an industrial process or controlling the industrial process using an active component of the field device; setting a switch of the field device to a current state corresponding to one of an open state in which power from an external power source is disconnected from the external device and a closed state in which power from the external power source is connected to the external device using a switch control signal generated by a controller of the field device; detecting an electrical parameter that is indicative of the current state of the switch using a switch monitor of the field device; generating a state output that is indicative of the current state of the switch based on the detected electrical parameter using the switch monitor, the state output being a first state output that is indicative of the open state of the switch when the switch is in the open state, a second state output that is indicative of the closed state of the switch when the switch is in the closed state, and a jitter state output that is indicative of the closed state of the switch when the switch is in the closed state, the jitter state output including a signal that alternates between the first state output and the second state output due to noise introduced to the switch monitor; generating a jitter-stable state output having a stable DC voltage based on the jitter state output that is indicative of the closed state of the switch using an anti-jitter circuit of the switch monitor; and ​ Using the controller, a notification is generated based on any of the first status output, the second status output, and the dithering stable state output, the notification indicating at least one of: the current state of the switch, a condition of the switch, and whether the status output is consistent with an expected state of the switch corresponding to a switch setting.

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