Monitoring of field device switches
The integration of a switch monitor with a chatter prevention circuit in field devices addresses switch failure detection issues, ensuring accurate and stable switch state monitoring, thus improving system reliability and reducing maintenance costs.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- ROSEMOUNT INC
- Filing Date
- 2022-05-26
- Publication Date
- 2026-07-08
AI Technical Summary
Existing industrial process control systems face challenges in efficiently monitoring and preventing failures of field device switches, leading to potential plant shutdowns, safety issues, and costly troubleshooting due to undetected switch malfunctions.
The implementation of a switch monitor with a chatter prevention circuit in field devices to accurately detect the state of switches and stabilize outputs, ensuring reliable operation by generating stable DC voltage under varying power conditions.
The solution provides reliable switch state monitoring, reducing false diagnostics and minimizing operational disruptions by stabilizing switch state outputs, thereby enhancing system reliability and reducing maintenance costs.
Smart Images
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Abstract
Description
Technical Field
[0001] Embodiments of the present disclosure relate to industrial process control systems. More specifically, embodiments of the present disclosure relate to industrial process field devices having a switch monitor for monitoring the state of switches of field devices.
Background Art
[0002] In industrial environments, control systems are used to monitor and control the status of industrial and chemical processes, etc. Typically, the control system uses industrial process field devices that are distributed at important positions within the industrial process and coupled to control circuits within the control system by process control loops to perform these functions. The term "field device" refers to any device that performs functions in a distributed control or process monitoring system, including all currently known or yet-to-be-known devices used for measuring, controlling, and / or monitoring industrial processes.
[0003] A typical field device includes device circuitry that enables the field device to perform tasks of conventional field devices such as monitoring and measuring process parameters using one or more sensors and / or performing 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 circuit of a field device may also include a controller used to control sensors and / or control devices, and may communicate with a process control system or other circuitry via a process control loop, such as a 4-20mA process control loop. In some installations, the process control loop is used to power the field device by supplying it with regulated current and / or voltage. The process control loop may also carry data, such as process parameter values corresponding to sensed process parameters. This data may be communicated via the process control loop as an analog signal or as a digital signal. [Overview of the Initiative]
[0005] Embodiments of the present disclosure relate 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 the process of the industrial process. Preferably, the switch is electrically coupled to a first terminal and a second terminal, and is 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. The switch monitor is configured to detect the current state of the switch corresponding to the closed or open state and to generate a state output indicating the current state. The state output is a first state output indicating the open state of the switch when the switch is in the open state, a second state output indicating the closed state of the switch when the switch is in the closed state and the switch is connected to DC, and a chattering state output indicating the closed state of the switch when the switch is in the closed state and the switch is connected to AC. The chatter prevention circuit of the switch monitor is configured to output a chatter-stable state output having a stable DC voltage based on the chattering state output. The controller is configured to set the switch to the open or closed state and to generate a notification based on one of the first state output, the second state output, and the chatter-stable state output indicating the current state and / or status of the switch.
[0006] One embodiment of the industrial process control system includes the field device, external device, and power supply described above. The external device is electrically connected to the switch via the first terminal. The power supply is electrically connected to the switch via the second terminal and is configured to supply power to the external device via the switch. Power is supplied to the external device when the switch is closed, and power is cut off from the external device when the switch is open.
[0007] In one embodiment of the method, process parameters of an industrial process are sensed, or the industrial process is controlled using the active component of the field device. The switch of the field device is set to a current state corresponding to an open state, where power from an external power source is cut off from the external device, or a closed state, where power from an external power source is connected to the external device, using a switch drive signal generated by the field device controller. The electrical parameters indicating the current state of the switch are detected using the switch monitor of the field device. Using the switch monitor, a state output indicating the current state is generated based on the detected electrical parameters, the state output being a first state output indicating the open state of the switch when the switch is in the open state, a second state output indicating the closed state of the switch when the switch is in the closed state and the power includes DC, and a chattering state output indicating the closed state of the switch when the switch is in the closed state and the power includes AC. Using the chatter prevention circuit of the switch monitor, a chatter-stable state output having a stable DC voltage is generated based on the chattering state output indicating the closed state of the switch. The controller generates a notification based on one of the first state output, the second state output, and the chatter stabilization state output, indicating the current state of the switch and / or the status of the switch.
[0008] This summary of the invention is provided to introduce, in a simplified form, a selection of concepts that will be further described in the detailed description below. This summary of the invention is not intended to identify any important or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. [Brief explanation of the drawing]
[0009] [Figure 1] This is a simplified diagram of an exemplary process control system according to an embodiment of the present disclosure. [Figure 2] This is a simplified diagram of an exemplary process control system according to an embodiment of the present disclosure. [Figure 3] This is a simplified block diagram of the switch monitor 140 according to an embodiment of the present disclosure. [Figure 4] This is a schematic diagram of an exemplary switch monitor for an industrial process field device according to an embodiment of the present disclosure. [Figure 5] This is a schematic diagram of an exemplary switch monitor for an industrial process field device according to an embodiment of the present disclosure. [Figure 6] The present disclosure includes charts of AC voltages delivered to a field device switch and charts of state outputs generated by an exemplary switch monitor of an industrial process field device. [Figure 7] This chart shows an example of the relationship between the switch control signal and the status output of the switch monitor in Figure 3 over time, when the monitored switches are powered by a 20VDC power supply and a 250VAC power supply, respectively, according to an embodiment of the present disclosure. [Figure 8] This chart shows an example of the relationship between the switch control signal and the status output of the switch monitor in Figure 3 over time, when the monitored switches are powered by a 20VDC power supply and a 250VAC power supply, respectively, according to an embodiment of the present disclosure. [Figure 9] This is a simplified circuit diagram of a switch monitoring circuit including a chatter prevention circuit according to an embodiment of the present disclosure. [Figure 10] This is a simplified circuit diagram of an example of a chatter prevention circuit according to an embodiment of the present disclosure. [Figure 11] This is the truth table for a Type D flip-flop. [Figure 12] This is the truth table for the chatter prevention circuit shown in Figure 10. [Figure 13] This is a series of charts illustrating simulation examples of the operation of switch monitor circuits and chatter prevention circuits. [Figure 14] This flowchart shows a method for controlling an external device using an industrial process field device according to an embodiment of the present disclosure. [Modes for carrying out the invention]
[0010] Embodiments of this disclosure are described in full below with reference to the accompanying drawings. Elements identified by the same or similar reference numerals refer to the same or similar elements. However, various embodiments of this disclosure may be embodied in many different forms and should not be construed as being limited to the embodiments described herein. Rather, these embodiments are provided so as to make this disclosure thorough and complete and to fully convey the scope of this disclosure to those skilled in the art.
[0011] Embodiments of this disclosure generally relate to industrial process field devices, industrial process control systems including the field devices, and methods for controlling external devices using the field devices. Figures 1 and 2 are simplified diagrams of an exemplary process measurement or control system 100 according to embodiments of this disclosure.
[0012] System 100 includes an industrial process field device 102 which may interact with an industrial process 104. In some embodiments, the process 104 includes a material, such as a fluid, which is processed by System 100, transported through pipes such as pipe 105 (Figure 1), and / or contained in a tank. This processing of the material generally converts the material from a lower-value state into a more valuable, useful product, such as petroleum, chemicals, paper, or food. For example, an oil refinery performs industrial processes that can process crude oil into gasoline, fuel oil, and other petrochemicals.
[0013] The field device 102 may communicate with a computerized control unit 106, which may be configured to control the field device 102. The control unit 106 may be located away from the field device, such as in the control room of the system 100, as shown in Figure 1.
[0014] The control unit 106 may be communicatively coupled to the field device 102 via a suitable physical or wireless communication link. For example, the control unit may be coupled to the field device via a control loop 107. Communication between the control unit 106 and the field device 102 may be performed via the control loop 107 according to conventional analog and / or digital communication protocols. In some embodiments, the process control loop 107 includes a 4-20 milliampere process control loop, and process variables may be represented by the level of the loop current I (Figure 2) flowing through the process control loop 107. Exemplary digital communication techniques include digital signals modulated to the analog current level of the two-wire process control loop 107, such as the HART® communication standard. Other purely digital techniques, including fieldbus and Profibus communication protocols, may also be used. The control unit 106 may include a power supply that provides power to the field device 102 via the control loop 107.
[0015] In some embodiments, the field device 100 includes, as shown in the schematic of FIG. 2, an active component in the form of a controller 108, one or more sensors or control devices 110, a measurement or control circuit 112, a digital - to - analog converter (DAC) 114, a communication circuit 115, and / or a terminal block 116. The controller 108 may represent one or more processors (i.e., microprocessors, central processing units, etc.) that control the components of the field device 100 to perform one or more of the functions described herein in response to the execution of instructions that may be locally stored in a non - transitory patent - eligible computer - readable medium or memory 118 of the device 100. In some embodiments, the processor of the controller 108 is a component of one or more computer - based systems. In some embodiments, the controller 108 includes one or more control circuits, microprocessor - based systems, field - programmable gate arrays (FPGAs), or other programmable hardware components used to control the components of the device 100 to perform one or more of the functions described herein. The controller 108 may also represent other conventional field - device circuits.
[0016] The field device 102 may be used to sense or measure parameters of the process 104, such as the temperature, level, pressure, flow rate, or another parameter of the process 104, using one or more sensors represented by block 110 of FIG. 2. Exemplary sensors 110 include pressure sensors, temperature sensors, level sensors, flow sensors, and / or other sensors used to sense or measure process parameters.
[0017] The field device 100 may also be configured to control aspects of the process 104 using one or more control devices represented by block 110 of FIG. 2. Exemplary control devices 110 include actuators, solenoids, valves, and other conventional process - control devices used in field devices to control a process.
[0018] The measurement or control circuit 112 represents a circuit that interacts with the sensor or control device 110. For example, the circuit 112 may include a measurement circuit that converts the output from the sensor 110 for use by the controller 108 of the field device. The DAC 114 may be used by the controller 108 to convert a digital signal into an analog signal that is communicated to the control unit 106 via the two-wire process control loop 107, for example, by adjusting the loop current I to indicate the value of the process parameter sensed by the sensor 110. The circuit 112 may also be used to control the control device 110, for example, in response to commands from the control unit 106 or other locations received by the controller 108 via the communication circuit 115.
[0019] Embodiments of the present disclosure are directed to a field device 102 that includes a switch 120. The switch 120 may be electrically coupled to a power source 124 and a device 126 external to the field device 102, such as via a terminal block 116. Accordingly, embodiments of the power source 124 and the device 126 are separate from the field device 102. The 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, a compressor, a solenoid, or another device suitable for use in the system 100.
[0020] The switch 120 may take any suitable form. For example, the switch 120 may include a latching relay or another suitable switch. Further, although only a single switch 120 is shown, it is understood that the field device 102 may be coupled to, for example, a terminal block 116 and include multiple switches 120 each controlled by the controller 108.
[0021] In some embodiments, the controller 108 selectively sets (i.e., controls, operates, or toggles) the switch 120 between a closed state, where the switch 120 connects the device 126 to power from the power supply 124, and an open state, where the switch 120 disconnects the device 126 from the power supply 124. Thus, the device 126 may be operated while the switch 120 is set to the closed state or in response to it, and the device 126 is stopped in response to the switch 120 being set to the open state. In some embodiments, the setting of the state of the switch 120 occurs in response to a switch drive or control signal 128 from the controller 108.
[0022] In some embodiments, the controller 108 is configured to set the switch 120 to either an open or closed state in response to a processor execution instruction based on one or more settings. The settings and programmed instructions may be stored as settings 130 in memory 118, in the memory of the control unit 106, and / or in another suitable location. Settings 130 may include user-defined settings such as thresholds and / or other switch control parameters.
[0023] In one embodiment, the controller 108 sets the switch 120 to an open or closed state in response to a sensed parameter (e.g., pressure, level, flow rate, temperature, etc.) detected by the sensor 110. For example, the controller 108 may compare the sensed parameter value output from the circuit 112 based on the parameter output from the sensor 110 with a setting 130 such as a user-defined threshold, and use a drive signal 128 to set the switch 120 to a predetermined open or closed state when the sensed parameter value satisfies a predetermined relationship with the threshold.
[0024] Alternatively, the control unit 106 may receive the sensed parameter value from the field device 102 and issue a command to the controller 108, such as via the control loop 107, to set the switch 120 to a desired state when the sensed parameter value satisfies a predetermined relationship with a setting 130, such as a user-defined threshold. The controller 108 then generates a drive signal 128 to set the switch 120 to the desired state in response to the command from the control unit 106.
[0025] In one example, the field device 102 may include a level sensor 110 that senses the level in the tank and communicates the sensed level to the control unit 106 using a communication circuit 115. When the level output generated by the sensor 110 indicates a sensed level below a threshold (e.g., setting 130), the controller 108 may be configured or commanded by the control unit 106 to set the switch 120 to the closed position to activate an external pump (device 126) and drive additional material into the tank. After the level sensed by the sensor 110 reaches another threshold level (setting 130), such as one indicating the tank is full, the controller 108 may be configured or commanded to open the switch 120 and deactivate the pump.
[0026] In another embodiment, the controller 108 uses a switch drive signal 128 to set the switch 120 to an open or closed state depending on the state of the control device 110. Alternatively, the control unit 106 may issue a command to the controller 108 to set the switch 120 to either an open or closed state based on the state of the control device 110. Here, the control device 110 includes at least two different states, such as the open or closed state of a valve, the position of an actuator or solenoid, or another state of the control device 110. For example, when the control device 110 is a valve and the device 126 is a pump, the controller 108 may be configured or commanded to set the switch 120 to a closed state when the valve is open and the pump is activated, driving a flow of material through the valve, and the controller 108 may be configured or commanded to set the switch 120 to an open position when the valve is closed and the pump is stopped.
[0027] It is crucial that the switch 120 operates correctly by achieving its intended open or closed state. An undetected failure of the switch 120 to enter a desired state set by the controller 108 can lead to a series of problems, including plant shutdowns and lengthy troubleshooting and repair efforts, such as safety issues, regulatory issues, process quality issues, and other potential problems. For example, if the controller 108 sends a drive signal 128 to transition the switch 120 from the closed to the open state in order to stop a pump (device 126) that fills a tank with fluid, but the switch 120 does not transition to the open state, the pump may continue to operate, potentially leading to the fluid overflowing from the tank, among other potentially problematic consequences. Such a switch failure generally requires immediate attention to mitigate potential damage. Unfortunately, providing sufficient manual monitoring of field devices 102 in an industrial system to identify a faulty or malfunctioning switch 120 is generally too time-consuming and costly.
[0028] Embodiments of the field device 102 according to this disclosure include a switch monitor 140 (Figure 2) which may be used to verify that the switch 120 of the field device 102 is operating as intended. The switch monitor 140 may be electrically coupled to the power supply 124 and the device 126, for example via a terminal block 116, as shown in Figure 2. In some embodiments, the switch monitor 140 is configured to handle the power supply 124 which provides a DC voltage such as direct current or 20 to 60 VDC, or an AC voltage such as alternating current or 20 to 250 VAC.
[0029] In some embodiments, the switch monitor 140 is configured to detect (e.g., sense or measure) the current state of the switch 120 (i.e., open or closed) and generate a state output 142 indicating the current state of the switch 120. The controller 108 is configured to generate a notification 144 based on the state output 142. The notification 144 may be transmitted to the control unit 106 or another location using, for example, a communication circuit 115, via a wired connection (e.g., a control loop 107) or a wireless communication link.
[0030] Embodiments of notification 144 indicate the current state of switch 120 and / or whether switch 120 is functioning properly (i.e., the status of switch 120). Notification 144 can take any suitable form. Exemplary notifications 144 include or trigger alarms (audible and / or visible), i.e., status reports presented on a display such as the display of control unit 106, analog or digital communications or messages via a wireless or wired communication link such as communications or settings delivered via process control loop 107, or other notifications. For example, notification 144 may be transmitted using communication circuit 115 by setting the loop current I to a predetermined level, or to one of a plurality of predetermined levels, each indicating a different notification.
[0031] In some embodiments, the controller 108 generates a notification 144 based on a comparison between a status output 142 and the intended state of the switch corresponding to the switch drive signal 128, which sets the state of the switch 120 based on the sensed parameters, commands, and / or the state of the control device, as described above. This comparison may be performed using a comparator circuit 146 that compares the status output 142 with the switch drive signal 128 and outputs a signal 148 based on that comparison. The signal 148 may indicate a correspondence between the switch drive signal 128 and the status output 142, such as when the switch drive signal 128 is configured to set the switch 120 to an open state and the status output 142 indicates that the switch 120 is in an open state. In this case, the switch 120 is presumed to be operating normally. Alternatively, the signal 148 may indicate a conflict between the switch drive signal 128 and the status output 142, such as when the switch drive signal 128 is configured to set the switch 120 to an open state and the status output 142 indicates that the switch 120 is in a closed state. In this case, it is presumed that switch 120 is operating improperly. Notification 144 may be generated by controller 108 in response to signal 148 to indicate the proper or improper operation of switch 120. Furthermore, notification 144 may indicate the current state of switch 120 as indicated by switch output 142, and / or the intended state of switch 120 corresponding to switch drive signal 128.
[0032] In some embodiments, the controller 108 generates a notification 144 based on a comparison between a status output 142 and a switch setting 150, which may be stored in memory 118, for example, as shown in Figure 2. The switch setting 150 indicates the intended or desired open or closed state of the switch 120. Thus, the switch setting 150 generally corresponds to a switch drive signal 128 that sets the state of the switch 120, and may be based on sensed parameters, the state of a control device, and / or commands, as described above. The controller 108 determines whether there is a correspondence between the switch setting 150 and the status output 142 indicating that the switch 120 is operating correctly, or whether there is a conflict between the switch setting 150 and the status output 142 indicating that the switch 120 is operating incorrectly. The notification 144 is generated by the controller 108 to indicate the correct or incorrect operation of the switch 120. Furthermore, the notification 144 may indicate the current state of the switch 120 indicated by the switch output 142, and / or the intended state of the switch 120 indicated by the switch setting 150.
[0033] In some embodiments, the switch monitor 140 includes a circuit that detects (i.e., senses or measures) an electrical parameter indicating the current state of the switch 120 (i.e., open or closed) and generates a state output 142 based on the detected electrical parameter. Embodiments of this electrical parameter include a voltage (AC or DC) across the switch 120, a current (AC or DC) through the switch 120, or another suitable electrical parameter. In some embodiments, the switch monitor 140 generates a state output 142 based on the detected electrical parameter indicating the current state of the switch 120.
[0034] In some embodiments, the state output 142 corresponds to two different voltage values, one of which is a fixed or stable logic or digital low voltage representing a digital 0 value, and the other is a fixed or stable logic or digital high voltage representing a digital 1 value. One of these values may be used to represent the open state of switch 120, and the other may be used to represent the closed state of switch 120. This choice may depend on the application (e.g., normally open vs. normally closed switch application). In this disclosure, the logic low voltage or digital 0 value is used to represent the open state of switch 120, and the logic high voltage or digital 1 value represents the closed state of switch 120.
[0035] Figure 3 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 a circuit forming a differential amplifier 151 and a comparator 152. The differential amplifier is connected to terminals 153 and 154 of a switch 120, which may be terminals of a terminal block 116 connected to a power supply 124, as shown in Figure 2, and to a load corresponding to an accessory device 126, and generates an output of a differential voltage 155 based on the voltage difference between terminals 153 and 154 or the current passing through the switch 120. The comparator generally compares the output from the differential amplifier with a reference voltage and generates a state output 142 based on the comparison.
[0036] Figures 4 and 5 are schematic diagrams of exemplary switch monitors 140A and 140B according to embodiments of the present disclosure. Exemplary switch monitor 140A is configured to generate a state output 142 based on the voltage (AC or DC) across switch 120, and exemplary switch monitor 140B generates a state output 142 based on the current I passing through switch 120. SIt is configured to generate a status output 142 (i.e., an analog voltage) based on (AC or DC). Switch monitors 140A and 140B are connected to terminals 153 and 154, respectively. The power supply 124 is generally represented by an AC or DC voltage source 156 and a resistor 158 coupled to terminal 153. Device 126 is electrically coupled to terminal 154 and the voltage source 156 or electrical ground / common.
[0037] In some embodiments, the differential amplifier 151 of the switch monitor 140A includes a voltage rectifier 160 that enables the switch monitor 140A to operate during the negative wave cycle of the AC waveform supplied by the power supply 124. In one exemplary embodiment, the rectifier 160 includes a diode 162 and a capacitor 164. The diode 162 blocks the negative cycle portion of the AC waveform generated by the power supply 124. The capacitor 164 is charged during the positive cycle of the AC waveform and slowly decays during the negative cycle of the AC waveform while the diode 162 blocks the waveform. The capacitor 164 is sized appropriately to substantially maintain the voltage charge achieved during the positive cycle of the AC waveform during the negative cycle of the AC waveform.
[0038] The 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 the power supply voltage Vs and a negative power supply input coupled to electrical ground 175. The ratio of resistors 166 and 170 to resistors 168 and 172 sets the gain of the op-amp 174 to detect the voltage difference across the switch 120 and between terminals 153 and 154, as indicated by the differential voltage output 155. The resistances of resistors 166, 168, 170, and 172 are high resistance to reduce high AC / DC sensing voltages to a level within the operating range of the low-voltage condition monitoring circuit.
[0039] The comparator 152 of the switch monitor 140A may include an operational amplifier 178 having a positive power supply input coupled to the power supply voltage Vs and a negative power supply input coupled to electrical ground 175. The operational amplifier 178 compares the voltage difference across the switch 120, indicated by the differential voltage output 155, with a threshold voltage set by a voltage divider formed by resistors 180 and 182, and outputs a state output 142 based on the comparison. The threshold voltage may be adjusted to correctly trigger over a range of voltages switched by the switch 120. Additional circuitry, such as that described later, may be used to process the output 142 before processing by the microprocessor of the controller 108, or to isolate the output 142.
[0040] Figure 6 shows two charts comparing the AC voltage from power supply 124 delivered to switch 120 with the state output 142 generated by the exemplary switch monitor 140A in Figure 4. During the period t0 to t1, switch 120 is in the open state, and the voltage across switch 120 reflects the AC voltage supplied by power supply 124. In this example, switch monitor 140A generates a logic low state output 142 for the open state of switch 120. At time t1, switch 120 is closed. This allows current to flow through switch 120 to device 126. Furthermore, the voltage across switch 120 drops to virtually zero. As a result of this change in the voltage across switch 120, switch monitor 140A generates a logic high state output 142.
[0041] An example switch monitor 140B (Figure 5) shows the current I passing through switch 120. S The switch 140B is configured to generate a status output 142 based on (AC or DC). The switch 140B includes a differential amplifier 151 coupled to terminals 153 and 154, which may be terminals of terminal block 116, for example, as shown in Figure 2. The differential amplifier 151 of the switch monitor 140B may also include a voltage rectifier 160 of circuit 140A formed by diodes 162 and capacitors 164 operating as described above.
[0042] 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 coupled to the power supply voltage Vs and a negative power supply input coupled to electrical ground 195. The ratio of resistors 186 and 190 to resistors 188 and 192 sets the gain of the operational amplifier 194 to detect the voltage difference across resistor 196 in series with the switch 120. The resistances of resistors 186, 188, 190, and 192 are high resistance to reduce high AC / DC sensing voltages to a level within the operating range of the low-voltage condition monitoring circuit. The operational amplifier 194 controls the current I S In response, a voltage difference signal 198 is output based on the voltage across resistor 196.
[0043] The signal 198 from the operational amplifier 194 of the differential amplifier 151 is an analog voltage proportional to the current through the resistor 196. Using the known value of the resistor 196 and the analog voltage of the state output 142, the comparator 152 may process the signal 198, compare it to a reference, and generate a corresponding state output 142, which may be processed by the controller 108. Additional circuitry may be used to process the output 142 before processing by the microprocessor of the controller 108, or to isolate the output 142. The controller 108 also acts as a comparator 152, processing the signal 198 from the differential amplifier 151 based on the value of the resistor 196, and the current I S You may decide on the current I. S The settings may be compared to determine whether the switch 102 (for example, a normally open switch or a normally closed switch) is in the open or closed state.
[0044] The above-described embodiment of the switch monitor 140 operates to provide a single detected level state output 142 for a wide range of input voltages from the power supply 124, such as DC voltages of 20–60VDC and AC voltages of 20–250VAC. Since the threshold of the comparator 152 must be set low enough to detect the possible range of voltages (e.g., 20–60VDC) across the switch 120 (e.g., across terminals 153 and 154), the switch monitor 140 may be susceptible to noise and AC coupling. As a result, when the switch 120 is closed (no voltage across the switch), digital output chattering of the state output 142 (i.e., continuous switching between high and low states) may occur instead of the desired fixed high output.
[0045] An example of a situation resulting in the chattering state output 142 will be explained with reference to Figures 7 and 8. Figures 7 and 8 are charts showing the relationship over time between the switch control signal 128 (Figure 2) and the state output 142 when the switch 120 is powered by a 20VDC power supply 124 and a 250VAC power supply 124, respectively. At time t0, when the switch control signal 128 changes the state of the switch 120 powered by the 20VDC power supply from open to closed, there is no longer a voltage difference across the switch 120, and as shown in Figure 7, a high logic voltage (digital 1) state output 142 is resulting at time t1.
[0046] 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, the state output chatters between low and high logic voltages starting from time t1, as shown in Figure 8, as a result of noise (e.g., EMC, AC coupling from adjacent switches or power supplies). When this chattering of the state output 142 occurs, the controller 108 may detect an incorrect reading of the state of switch 120 and issue a false notification 144 of a switch failure. Such a false diagnostic notification 144 can have serious adverse effects, such as process shutdown, wasted time and expense investigating the failure notification, and reduced reliability of the performance of the field device 102.
[0047] In some embodiments, the switch monitor 140 includes a chatter prevention circuit that operates to stabilize the chattering state output 142 under closed switch and specific AC voltage power conditions, while generally passing or regenerating the state output 142 under other power and state conditions of the switch 120.
[0048] This modification is shown in its entirety in the simplified circuit diagram of Figure 9. The chatter prevention circuit 200 receives the status output 142 and generates a stable status output 142' in response. Here, the differential amplifier 151 and comparator 152 operate substantially as described above, for example with reference to Figures 3 to 6, and generate the status output 142 according to the sensed conditions. The stable status output 142' replaces the status output 142 in Figure 2 and is used by the controller 108 to determine the current state of the switch 120 and generate a notification 144, as described above.
[0049] When switch 120 is in the open state, when switch 120 is connected to a 20-60VDC power supply 124, or under other scenarios that do not generate a chattering state output 142, the stable state output 142' generated by the dechattering circuit 200 generally reflects the stable state output of state output 142. That is, the stable state output substantially reflects the state output when state output 142 is either a fixed or stable logic low or logic high voltage signal. However, when switch 120 is closed and coupled to 20-250VAC such as 250VAC, and state output 142 is chattering, the stable state output 142' generated by the dechattering circuit 200 corresponds to the desired logic voltage output (e.g., a fixed high logic voltage) of the expected correct state signal 142 for the closed state of switch 120. As a result, the dechattering circuit 200 corrects the aforementioned malfunction and reduces the likelihood of the field device 102 issuing a misdiagnosis notification 144.
[0050] The chatter prevention circuit 200 can take many forms. An example of the circuit 200 is shown in a simplified diagram in Figure 10, in which a D-type flip-flop 204 is used. Figure 11 is the truth table for the D-type flip-flop 204.
[0051] As shown in Figure 10, the D input of the flip-flop 204 is a digital high voltage (V DD ) is pulled. The state output 142 from the switch monitor 140 drives the clock pin (CLK) of the flip-flop 204. The clear pin (CLR) of the flip-flop 204 is used to reset the output of the circuit 200 using the switch control signal 128. This allows the Q output of the flip-flop 204 to remain high when the rising edge is detected in the state output 142, and the stable state output 142' is read by the controller 108 with each state change so that the pulse clears the Q output to a logic or digital low voltage before each measurement.
[0052] During operation, when the controller 108 issues a state control signal 128 (e.g., a voltage pulse) to change the state of the switch 120, the state control signal 128 also clears the Q output of the flip-flop 204 due to its connection 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.
[0053] Since the D input is pulled to a logic voltage high, the Q output remains low or transitions to high based on the presence of a rising edge on the CLK input driven by the state output 142. The truth table shown in Figure 12 shows that if the state output 142 (CLK input) is chattering (Figure 8) due to the closed state of switch 120 and AC power to the switch terminals 153 and 154, the Q output transitions to high and remains high, thereby eliminating the chattering and generating the desired logic high voltage to indicate the closed state of switch 120.
[0054] In some embodiments, after the controller 108 transmits a switch control signal or pulse 128, it waits for a short time before measuring the stable state output 142' to allow the switch monitor 140 and the chatter prevention circuit 200 to stabilize.
[0055] In some embodiments, the chatter prevention circuit includes an OR gate 206 that receives the Q output and state output 142 from the flip-flop 204 and operates to prevent false tripping in the initial state in which switch 120 is closed. For example, if switch 120 and the power supplied to switch 120 are initially in the closed state, the state output 142 will be a logic high voltage. However, during initial startup, the switch control signal 128 may clear the Q output to a logic low voltage, and since there is never a rising edge on the clock input (CLK), Q remains a logic low voltage, but it must be a logic high voltage to indicate that switch 120 is closed. By supplying the Q output and state output 142 to the OR gate 206, this situation is resolved, and the final stable state output 142' remains high during this startup period and thus indicates the correct state of switch 120.
[0056] Figure 13 includes a series of charts illustrating a simulated example of the operation of the switch monitor 140 and the chatter prevention circuit 200 when power supply 124 supplies AC power to terminals 153 and 154 of switch 120 connected to a load or device 126. Parasitic capacitance and AC noise were added to the simulation to trip a threshold during switch closure.
[0057] First, the controller 108 generates a switch control signal or pulse 128 to change the switch 120 from an open state to a closed state. This closing of the switch is shown by a plot of the current flowing through the switch 120.
[0058] As shown in the chart, these events result in a chattering state output 142 from the switch monitor 140. However, the dechatter prevention circuit 200 eliminates the chattering of state output 142, resulting in a fixed, stable state output 142'. Immediately after another switch control signal or pulse 128 is generated by the controller 128, the switch 120 is opened, and both state output 142 and stable state output 142' transition to a logic low voltage.
[0059] Further embodiments of this disclosure relate to a method for controlling an external device 126 using an industrial process field device 102 formed according to one or more embodiments described herein. Figure 14 is a flowchart of one embodiment of the method.
[0060] In method 210, process parameters of the industrial process 104 are sensed, or the process 104 is controlled using the active component 110 of the field device 102. Therefore, the active component may be in the form of a sensor that senses process parameters, or a control device that controls the process, as described above.
[0061] In 212, the switch 120 of the field device 102 is set to a current state corresponding to either an open state, where power from the external power supply 124 is disconnected from the external device 126, or a closed state, where power from the external power supply 124 is connected to the external device 126. In some embodiments, the switch 120 is set to the current state in response to a switch control signal 128 generated by the controller 108 of the field device 102, as described above.
[0062] In 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 the switch 120. As described above, embodiments of these electrical parameters include the voltage (AC or DC) across the switch 120 and the current (AC or DC) passing through the switch 120.
[0063] In 216, a state output 142 indicating the current state based on the detected electrical parameters is generated using the switch monitor 140. The state output 142 includes a first state output, such as a logical low voltage, indicating the open state of switch 120 when switch 120 is open; a second state output, such as a logical high voltage, indicating the closed state of switch 120 when switch 120 is closed and the power supplied by the power supply 124 includes DC; and a chattering state output indicating the closed state of switch 120 when switch 120 is closed and the power includes AC.
[0064] In 218, based on the chattering state output indicating the closed state of switch 120, the chatter prevention circuit 200 of the switch monitor 140 generates a chatter-stable state output 142' having a stable DC voltage.
[0065] In 220, the controller 108 is used to generate a notification based on one of the first state output, the second state output, and the chatter-stable state output. Each of these state outputs may be generated by the chatter prevention circuit 200 based on the state output 142. As described above, the notification 144 may indicate the current state of the switch 120 and / or whether the switch 120 is operating properly.
[0066] While embodiments of this disclosure have been described with reference to preferred embodiments, those skilled in the art will recognize that modifications can be made in form and detail without departing from the spirit and scope of this disclosure.
Claims
1. Active components selected from the group consisting of sensors configured to sense process parameters and control devices configured to control the process of an industrial process, A switch electrically coupled to a first terminal and a second terminal, 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 the electrical parameters of the switch, wherein the state output is a first state output indicating the open state of the switch when the switch is in the open state, a second state output indicating the closed state of the switch when the switch is in the closed state, and a chattering state output indicating the closed state of the switch when the switch is in the closed state, the chattering state output includes a signal that alternates between the first state output and the second state output as a result of noise introduced into the switch monitor, A chatter prevention circuit of the switch monitor is configured to output a chatter-stable state output having a stable DC voltage based on the chatter-state output indicating the closed state of the switch, and A controller configured to set the switch to one of the open and closed states based on the output or state of the active component, and to generate a notification based on one of the first state output, the second state output, and the chatter-stable state output, indicating at least one of the current state of the switch and whether the switch is operating properly. Field devices for industrial processes, including those mentioned above.
2. One of the first state output and the second state output includes a logic low voltage. The other of the first state output and the second state output includes a logic high voltage. The chattering signal includes a voltage that alternates between the logic low voltage and the logic high voltage. The field device according to claim 1.
3. The aforementioned switch monitor is A differential amplifier configured to output a differential voltage based on the voltage difference between the first terminal and the second terminal of the switch or the current passing through the switch, and The field device according to claim 2, comprising a comparator configured to output one of the first state output, the second state output, and the chattering state signal based on the differential voltage.
4. The field device according to claim 3, wherein the chatter prevention circuit is configured to output a first stable state output that substantially reflects the first state output based on the first state output, and to output a second stable state output that substantially reflects the second state output based on the second state output.
5. The controller uses a switch control signal to set the switch to the open or closed state. The chatter prevention circuit comprises a D-type flip-flop having a clear (CLR) input for receiving the switch control signal, a clock (CLK) input for receiving the status output, and a D input for receiving a logic high voltage. The chatter stable state output, the first stable state output, and the second stable state output are generated at the Q output of the flip-flop based on the state output. The field device according to claim 4.
6. The field device according to claim 5, wherein the chatter prevention circuit includes an OR gate connected to the Q output and the state output.
7. The field device according to claim 4, wherein the controller generates the notification based on a comparison between one of the first stable state output, the second stable state output, and the chatter stable state output and a switch setting indicating the intended state of the switch.
8. The controller is configured to set the switch to the open or closed state using a switch control signal. The controller generates the notification based on a comparison between one of the first stable state output, the second stable state output, and the chatter stable state output and the switch control signal. The field device according to claim 4.
9. The controller is configured to set the switch to the open or closed state using a switch control signal. The active component includes the sensor having a parameter output corresponding to the sensed process parameter, The controller is configured to use the switch control signal to set the switch to either the open or closed state based on the parameter output. The field device according to claim 1.
10. The system further includes a measurement circuit configured to convert the parameter output into a parameter value for use by the controller, The aforementioned sensor is selected from the group consisting of a pressure sensor, a level sensor, a flow sensor, and a temperature sensor. The controller is configured to communicate the parameter values and notifications to a remote location using a communication circuit. The field device according to claim 9.
11. The controller is configured to set the switch to the open or closed state using a switch control signal. The active component comprises the control device selected from the group consisting of actuators, valves, and solenoids. The control device includes at least two different states, The controller is configured to use the switch control signal to set the switch to either the open state or the closed state based on the state of the control device. The field device according to claim 1.
12. Active components selected from the group consisting of sensors configured to sense process parameters and control devices configured to control the process of an industrial process, A switch electrically coupled to a first terminal and a second terminal, 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 the electrical parameters of the switch, wherein the state output is a first state output indicating the open state of the switch when the switch is in the open state, a second state output indicating the closed state of the switch when the switch is in the closed state, and a chattering state output indicating the closed state of the switch when the switch is in the closed state, the chattering state output includes a signal that alternates between the first state output and the second state output as a result of noise introduced into the switch monitor, A chatter prevention circuit of the switch monitor is configured to output a chatter-stable state output having a stable DC voltage based on the chatter-state output indicating the closed state of the switch, and A controller configured to set the switch to one of the open and closed states based on the output or state of the active component, and to generate a notification based on one of the first state output, the second state output, and the chatter-stable state output, indicating at least one of the current state of the switch and whether the switch is operating properly. Field devices including, and An external device electrically coupled to the switch via the first terminal, and Includes a power supply that is electrically coupled to the switch via the second terminal and configured to supply power to the external device via the switch, When the switch is in the closed state, power is supplied to the external device, and when the switch is in the open state, power is cut off from the external device. Industrial process control system.
13. One of the first state output and the second state output includes a logic low voltage. The other of the first state output and the second state output includes a logic high voltage, and The chattering signal includes a voltage that alternates between the logic low voltage and the logic high voltage. The system according to claim 12.
14. The switch monitor includes a differential amplifier configured to output a differential voltage based on the voltage difference between the first and second terminals of the switch or the current flowing through the switch, and Based on the differential voltage, the first state output, the second state output, and the chatter A comparator configured to output one of the ring-state signals, including, The system according to claim 13.
15. The system according to claim 14, wherein the chatter prevention circuit is configured to output a first stable state output that substantially reflects the first state output based on the first state output, and to output a second stable state output that substantially reflects the second state output based on the second state output.
16. The controller uses a switch control signal to set the switch to the open or closed state. The chatter prevention circuit comprises a D-type flip-flop having a clear (CLR) input for receiving the switch control signal, a clock (CLK) input for receiving the status output, and a D input for receiving a logic high voltage. The chatter stable state output, the first stable state output, and the second stable state output are generated at the Q output of the flip-flop based on the state output. The system according to claim 15.
17. The system according to claim 16, wherein the chatter prevention circuit includes an OR gate connected to the Q output and the state output.
18. The system according to claim 15, wherein the controller generates the notification based on a comparison between any one of the first stable state output, the second stable state output, and the chatter stable state output and a switch setting indicating the intended state of the switch.
19. The controller is configured to set the switch to the open or closed state using a switch control signal. The controller generates the notification based on a comparison between one of the first stable state output, the second stable state output, and the chatter stable state output and the switch control signal. The system according to claim 15.
20. A method for controlling an external device using an industrial process field device, Using the active components of a field device to sense process parameters of an industrial process, or to control the industrial process, Using the switch control signal generated by the field device controller and the output or state of the active component, set the switch of the field device to a current state corresponding to either an open state where power from the external power supply is cut off from the external device, or a closed state where power from the external power supply is connected to the external device. Using the switch monitor of the field device, detect the electrical parameters indicating the current state of the switch. Using the switch monitor, a state output indicating the current state is generated based on the detected electrical parameters, wherein the state output includes a first state output indicating the open state of the switch when the switch is in the open state, a second state output indicating the closed state of the switch when the switch is in the closed state, and a chattering state output indicating the closed state of the switch when the switch is in the closed state, the chattering state output includes a signal that alternates between the first state output and the second state output as a result of noise introduced into the switch monitor. Using the chatter prevention circuit of the switch monitor, before indicating the closed state of the switch Based on the recorded chattering state output, a chatter-stable state output having a stable DC voltage is generated, and Using the controller, generate a notification indicating at least one of the current state of the switch and whether the switch is operating properly, based on any one of the first state output, the second state output, and the chatter stabilization state output. Methods that include...