field device

Abstract

The present application provides a field device including: a current control section that operates with a first power supply voltage, outputs a control signal that controls a current to be output to a transmission line; a current output section that operates with a second power supply voltage different from the first power supply voltage, and is capable of outputting a current of a magnitude corresponding to the control signal output from the current control section to the transmission line; and an abnormality notification section that outputs a first signal indicating a burnout current in which an abnormality has occurred to the current output section in a case where the first power supply voltage has an abnormality.

Description

Technical Field

[0001] This invention relates to a field device.

[0002] This application claims priority to Japanese Patent Application No. 2020-178884, filed on October 26, 2020, the contents of which are incorporated herein by reference. Background Technology

[0003] In factories or workshops, distributed control systems (DCS) are built to achieve a high degree of automation. A DCS is a system in which field devices (e.g., measuring instruments, manipulators) and control devices that control them are connected via communication units. One type of field device used in such a system is a two-wire transmitter that transmits analog signals corresponding to measured process values ​​(e.g., pressure, flow rate, temperature, etc.) to the control device via a two-wire transmission line.

[0004] Japanese Patent Publication No. 9-81883 discloses a conventional two-wire transmitter. This two-wire transmitter includes: a current control unit (digital circuit) that controls the current to be output to the transmission line; and a current output unit (analog circuit) that outputs a current corresponding to the control signal output from the current control unit to the transmission line. Furthermore, under normal conditions, the current output unit outputs a current in the range of, for example, 4 to 20 mA; under abnormal conditions (e.g., power failure), the current output unit outputs a current of, for example, less than 3.6 mA or more than 21.6 mA (burnout output).

[0005] Furthermore, the two-wire transmitter disclosed in Japanese Patent Publication No. 9-81883 includes a first power supply circuit that generates a first power supply voltage to operate the current control unit, and a second power supply circuit that generates a second power supply voltage to operate the current output unit. In this case, if the second power supply voltage drops due to an abnormality in the second power supply circuit, a control signal for cutting off the output is output from the current control unit, and the output is cut off via the current output unit. This notifies the control device connected to the two-wire transmitter that an abnormality has occurred in the field equipment.

[0006] However, in the event of an anomaly in the first power supply circuit, the first power supply voltage may sometimes exceed the voltage range within which the current control unit can operate, causing the current control unit to malfunction. In this situation, the following problem arises: the control device connected to the two-wire transmitter cannot be notified of the anomaly in the field equipment. Summary of the Invention

[0007] To address the aforementioned issues, one aspect of the present invention provides a field device (1-4) comprising: a current control unit (240, 240C) that operates on a first power supply voltage (V1) and outputs a control signal controlling the current to be output to transmission lines (L1, L2); a current output unit (260) that operates on a second power supply voltage (V2) different from the first power supply voltage and is capable of outputting a current corresponding to the magnitude of the control signal output from the current control unit to the transmission lines; and an abnormality notification unit (250) that, in the event of an abnormality in the first power supply voltage, outputs a first signal (P) to the current output unit to indicate that an abnormality has occurred, thereby causing the current output unit to output a burnout current.

[0008] Furthermore, in one aspect of the field device of the present invention, when the second power supply voltage is abnormal, the current control unit outputs a second signal for causing the current output unit to output the burn-out current as the control signal.

[0009] Furthermore, one aspect of the field device of the present invention further includes: a first power monitoring unit (220) that outputs a first abnormal signal indicating an abnormality of the first power supply voltage when the first power supply voltage is outside a predetermined first voltage range; and a second power monitoring unit (221) that outputs a second abnormal signal indicating an abnormality of the second power supply voltage when the second power supply voltage is outside a predetermined second voltage range.

[0010] Furthermore, in one aspect of the field device of the present invention, the abnormality notification unit outputs the first signal to the current output unit when the first abnormality signal is input and the second abnormality signal is not input.

[0011] Furthermore, in one aspect of the field device of the present invention, the abnormality notification unit outputs the second signal to the current output unit when the first abnormality signal is not input and the second abnormality signal is input.

[0012] Alternatively, in a field device according to one aspect of the present invention, when both the first abnormal signal and the second abnormal signal are input, the abnormality notification unit outputs a third signal to the current output unit to cause the current output unit to output a starting current, wherein the starting current is the current required to start the field device.

[0013] Furthermore, one aspect of the field device of the present invention also includes a start circuit (300) that delays the input of the second abnormal signal to the abnormal notification unit for a certain period of time.

[0014] Furthermore, one aspect of the field device of the present invention further includes a sensor module (100), which operates by a third power supply voltage different from the first power supply voltage and the second power supply voltage, and outputs a sensor value representing the measurement result of the sensor (S). The current control unit outputs a PWM (Pulse Width Modulation) signal having a pulse width corresponding to the sensor value output from the sensor module as the control signal, and the current output unit outputs a current corresponding to the pulse width of the PWM signal to the transmission line.

[0015] Furthermore, in one aspect of the field device of the present invention, the first signal and the second signal are signals having pulse widths different from those obtainable from sensor values ​​output from the sensor module.

[0016] Furthermore, one aspect of the field device of the present invention further includes: a communication unit (230) for communication between the sensor module and the current control unit; and a third power supply monitoring unit (500) for stopping the operation of the communication unit in the event of an abnormality in the third power supply voltage, wherein the current control unit outputs the second signal when the communication unit stops operating.

[0017] Furthermore, one aspect of the field device of the present invention also includes a power cut-off unit (400), which, in the event of an abnormality in the first power supply voltage or the second power supply voltage, at least cuts off the supply of the third power supply voltage to the sensor module.

[0018] Furthermore, in one aspect of the field device of the present invention, the abnormality notification unit includes: a pulse signal generating unit (252) for generating a pulse signal; and a clock signal generating unit (251) for generating a clock signal, wherein the first signal is the pulse signal generated by the pulse signal generating unit, and the third signal is the clock signal generated by the clock signal generating unit.

[0019] Furthermore, in one aspect of the field device of the present invention, the abnormality notification unit includes a first selector (255), which selects either the pulse signal generated by the pulse signal generation unit or the clock signal generated by the clock signal generation unit.

[0020] Furthermore, in a field device according to one aspect of the present invention, the first selector selects the clock signal generated by the clock signal generation unit when both the first abnormal signal and the second abnormal signal are input, and selects the pulse signal generated by the pulse signal generation unit in other cases.

[0021] Furthermore, one aspect of the field device of the present invention further includes a sensor module (100), which operates by a third power supply voltage different from the first power supply voltage and the second power supply voltage, and outputs a sensor value representing the measurement result of the sensor. The current control unit outputs a PWM signal having a pulse width corresponding to the sensor value output from the sensor module as the control signal. The abnormal notification unit further includes a second selector (256), which selects either the signal selected by the first selector or the PWM signal output from the current control unit.

[0022] Furthermore, in one aspect of the field device of the present invention, the startup circuit is a hysteresis comparator or a Schmitt trigger.

[0023] Furthermore, one aspect of the field device of the present invention further includes a transmission unit (200), which includes the current control unit, the current output unit and the abnormal notification unit. The transmission unit is separated from the sensor module and connected to the sensor module via a cable (L3). The sensor module outputs the sensor value to the communication unit via the cable.

[0024] Furthermore, in one aspect of the field device of the present invention, the power cut-off unit includes a switch (420), which is in a conducting state when the first power supply voltage and the second power supply voltage are normal, and in a disconnected state when at least one of the first power supply voltage or the second power supply voltage is abnormal.

[0025] Furthermore, in one aspect of the field device of the present invention, when the switch is in the on state, the third power supply voltage is supplied to the sensor module, and when the switch is in the off state, the power cut-off part cuts off the supply of the third power supply voltage to the sensor module.

[0026] Furthermore, the field device of one aspect of the present invention further includes: a first power supply circuit (210) for generating the first power supply voltage by stepping down the second power supply voltage; and a second power supply circuit (211) for generating the second power supply voltage based on power supplied from an external device.

[0027] According to the present invention, the following effect is achieved: even if the power supply voltage supplied to the current control unit that controls the current to be output to the transmission line is abnormal, the abnormality can be notified to an external device.

[0028] Further features and aspects of the invention will become apparent from the detailed description of the embodiments described below with reference to the accompanying drawings. Attached Figure Description

[0029] Figure 1 This is a block diagram illustrating the essential components of the field device according to the first embodiment of the present invention.

[0030] Figure 2 This is a timing diagram of various signals of the field device according to the first embodiment of the present invention.

[0031] Figure 3 This is a diagram showing the status of various signals of the field device according to the first embodiment of the present invention.

[0032] Figure 4 This is a block diagram illustrating the essential components of the field device according to the second embodiment of the present invention.

[0033] Figure 5 This is a circuit diagram illustrating an example of the start-up circuit of a field device provided in the second embodiment of the present invention.

[0034] Figure 6 This is a block diagram illustrating the essential components of the field device according to the third embodiment of the present invention.

[0035] Figure 7 This is a block diagram illustrating the essential components of the field device according to the fourth embodiment of the present invention. Detailed Implementation

[0036] Embodiments of the present invention will be described with reference to preferred embodiments. Those skilled in the art will be able to implement various alternatives to these embodiments using the teachings of the present invention, and the present invention is not limited to the preferred embodiments described herein.

[0037] One aspect of the present invention provides a field device that can notify an external device of an anomaly even if an abnormality occurs in the power supply voltage supplied to a current control unit that controls the current to be output to the transmission line.

[0038] The field device according to embodiments of the present invention will now be described in detail with reference to the accompanying drawings. First, an overview of the embodiments of the present invention will be given, followed by a detailed description of each embodiment.

[0039] [summary]

[0040] A two-wire transmitter, a type of field device, includes: a current control unit that outputs a control signal to control the current to be output to the transmission line; and a current output unit that outputs a current corresponding to the magnitude of the control signal output from the current control unit to the transmission line. In this two-wire transmitter, the current control unit outputs a PWM (Pulse Width Modulation) signal with a pulse width corresponding to a sensor value representing a measurement result from a sensor as a control signal, and a current (e.g., a current in the range of 4 to 20 mA) corresponding to the pulse width of the PWM signal is output to the transmission line from the current output unit.

[0041] Furthermore, in the event of an anomaly such as a power supply failure, this two-wire transmitter can output a current indicating an anomaly (e.g., a current of 3.6mA or less or a current of 21.6mA or more) (output cut-off). In the case of output cut-off, a signal with a pulse width different from the pulse width obtainable from the sensor value is output from the current control unit to the current output unit.

[0042] Here, the current control unit is a digital circuit that operates on a first power supply voltage. In contrast, the current output unit is an analog circuit that operates on a second power supply voltage different from the first power supply voltage. When the second power supply voltage drops, a control signal for cutting off the output is output from the current control unit, and the output is cut off via the current output unit. This notifies the control device connected to the two-wire transmitter of an anomaly in the field equipment. However, sometimes the current control unit fails to operate properly when the first power supply voltage drops. In this case, it cannot notify the control device connected to the two-wire transmitter of an anomaly in the field equipment.

[0043] Furthermore, in existing two-wire transmitters, only decreases in the first and second power supply voltages are detected; increases in either voltage are not detected. Therefore, if the first or second power supply voltage rises above a predetermined value, no abnormality is detected, and thus no notification of an anomaly is sent to the control device connected to the two-wire transmitter.

[0044] Furthermore, in existing two-wire transmitters, since a large current is required during startup, control is implemented to ensure that the current output unit outputs the current required for startup, i.e., the startup current. For example, control is implemented to ensure that the current output unit outputs 50% of the current in the range of 4 to 20 mA (12 mA) as the startup current. This control is necessary for reliably starting the two-wire transmitter, and therefore, it is also necessary to maintain this control when improving the two-wire transmitter.

[0045] In one embodiment of the present invention, the system includes: a current control unit that operates on a first power supply voltage and outputs a control signal that controls the current to be output to the transmission line; a current output unit that operates on a second power supply voltage different from the first power supply voltage and is capable of outputting a current corresponding to the magnitude of the control signal output from the current control unit to the transmission line; and an abnormality notification unit that, in the event of an abnormality in the first power supply voltage, causes the current output unit to output a first signal indicating that an abnormality has occurred, thus preventing current loss. Therefore, even if an abnormality occurs in the power supply voltage supplied to the current control unit that controls the current to be output to the transmission line, an external device can be notified of the abnormality.

[0046] [First Implementation Method]

[0047] <Field Equipment>

[0048] Figure 1 This is a block diagram illustrating the essential components of the field device according to the first embodiment of the present invention. For example... Figure 1 As shown, the field device 1 of this embodiment includes a sensor module 100 and a transmission unit 200, which are connected to an external device C via two transmission lines L1 and L2. The external device C is, for example, a control device that forms the core of a distributed control system. This field device 1 operates by supplying current from the external device C via the two transmission lines L1 and L2, and by controlling the current flowing through the two transmission lines L1 and L2, it outputs a sensor value representing the measurement result of the sensor S to the external device C.

[0049] The sensor module 100 includes a power supply circuit 110, a power monitoring unit 120, and a calculation unit 130, and obtains sensor values ​​representing the measurement results of the sensor S. The power supply circuit 110 generates a power supply voltage Vs, which serves as the operating power supply for the sensor module 100, based on the power supplied from the transmission unit 200. The power supply voltage Vs is supplied to various components constituting the sensor module 100, including the power monitoring unit 120 and the calculation unit 130. The power monitoring unit 120 monitors the power supply voltage Vs generated by the power supply circuit 110. The calculation unit 130 obtains the measurement results of the sensor S (e.g., measurement results of temperature, pressure, flow rate, etc.), and performs A / D conversion (analog-to-digital conversion) on the obtained measurement results to obtain the sensor values.

[0050] The transmission unit 200 includes: power supply circuits 210-214, power monitoring units 220-222, a communication unit 230, a current control unit 240, an abnormality notification unit 250, and a current output unit 260. This transmission unit 200 controls the current flowing through the two transmission lines L1 and L2 based on sensor values ​​obtained from the sensor module 100, thereby outputting the sensor values ​​to the external device C. Furthermore, in the event of an abnormality in the power supply circuits (e.g., power supply circuits 210 and 211), the transmission unit 200 outputs this information to the external device C.

[0051] When outputting sensor values ​​to an external device C, the transmission unit 200, for example, controls the current flowing through the two transmission lines L1 and L2 to converge within the range of 4 to 20 mA. Furthermore, if an abnormality occurs in the power supply circuit to the external device C, the transmission unit 200, for example, outputs a current of 3.6 mA or less, or a current of 21.6 mA or more (burnout current).

[0052] The power supply circuit 210 generates a power supply voltage V1 (first power supply voltage), which becomes the operating voltage of the current control unit 240. Specifically, the power supply circuit 210 generates the power supply voltage V1 by stepping down the power supply voltage V2 (second power supply voltage) generated by the power supply circuit 211. For example, if the power supply voltage V2 is 5.5V, the power supply circuit 210 generates a power supply voltage V1 of 3.0V. The power supply circuit 211 generates the power supply voltage V2, which becomes the operating voltage of the current output unit 260, based on the power supplied from the external device C via transmission lines L1 and L2.

[0053] Power supply circuit 212 generates a power supply voltage V3, which becomes the operating voltage of the fault notification unit 250. Specifically, power supply circuit 212 generates power supply voltage V3 by stepping down the power supply voltage V2 generated by power supply circuit 211. For example, power supply circuit 212 generates a power supply voltage V3 of 2.5V. Power supply circuit 213 generates a power supply voltage V4, which becomes the operating voltage of a display (not shown) installed in field device 1. Specifically, power supply circuit 213 generates power supply voltage V4 by stepping down the power supply voltage V2 generated by power supply circuit 211. For example, power supply circuit 213 generates a power supply voltage V4 of 5.0V.

[0054] Power supply circuit 214 generates a power supply voltage V5 (third power supply voltage) that becomes the operating voltage of sensor module 100. Power supply circuit 214 generates power supply voltage V5 by stepping down the power supply voltage V4 generated by power supply circuit 213. For example, power supply circuit 214 generates a power supply voltage V5 of 3.2V. Power supply circuit 214, for example, has an insulated transformer, with its primary side connected to power supply circuit 213 and its secondary side connected to power supply circuit 110 of sensor module 100. Therefore, by supplying power supply voltage V5 from power supply circuit 214 to power supply circuit 110, power supply voltage Vs is generated.

[0055] The power monitoring unit 220 (first power monitoring unit) monitors the power supply voltage V1 and outputs a signal M1 indicating whether the power supply voltage V1 is abnormal to the abnormality notification unit 250. If the power supply voltage V1 is outside the first voltage range, the power monitoring unit 220 outputs a signal indicating an abnormality in the power supply voltage V1 (first abnormality signal) to the abnormality notification unit 250. An abnormality in the power supply voltage V1 refers to a situation where the power supply voltage V1 is overvoltage or undervoltage. Furthermore, the signal indicating the aforementioned abnormality in the power supply voltage V1 is a low-level signal.

[0056] Here, the aforementioned first voltage range is the range between the upper threshold Vth11 and the lower threshold Vth12. When the power supply voltage V1 exceeds the upper threshold Vth11, the power supply voltage V1 is considered overvoltage, and the power monitoring unit 220 outputs a low-level signal M1. Conversely, when the power supply voltage V1 is less than the lower threshold Vth12, the power supply voltage V1 is considered undervoltage, and the power monitoring unit 220 outputs a low-level signal M1. On the other hand, when the power supply voltage V1 is within the first voltage range, the power supply voltage V1 is not abnormal, and the power monitoring unit 220 outputs a high-level signal M1 indicating that the power supply voltage V1 is normal.

[0057] The power monitoring unit 221 (second power monitoring unit) monitors the power supply voltage V2 and outputs a signal M2 indicating whether the power supply voltage V2 is abnormal to the current control unit 240 and the abnormality notification unit 250. If the power supply voltage V2 is outside the second voltage range, the power monitoring unit 221 outputs a signal indicating an abnormality in the power supply voltage V2 (second abnormality signal) to the current control unit 240 and the abnormality notification unit 250. An abnormality in the power supply voltage V2 refers to a situation where the power supply voltage V2 is overvoltage or undervoltage. Furthermore, the signal indicating the aforementioned abnormality in the power supply voltage V2 is a low-level signal.

[0058] Here, the aforementioned second voltage range is the range between the upper threshold Vth21 and the lower threshold Vth22. When the power supply voltage V2 exceeds the upper threshold Vth21, the power supply voltage V2 is considered overvoltage, and the power monitoring unit 221 outputs a low-level signal M2. Conversely, when the power supply voltage V2 is less than the lower threshold Vth22, the power supply voltage V2 is considered undervoltage, and the power monitoring unit 221 outputs a low-level signal M2. On the other hand, when the power supply voltage V2 is within the second voltage range, the power supply voltage V2 is not abnormal, and the power monitoring unit 221 outputs a high-level signal M2 indicating that the power supply voltage V2 is normal.

[0059] The power monitoring unit 222 monitors the power supply voltage V4 and outputs a signal indicating whether the power supply voltage V4 is abnormal to the current control unit 240 and the abnormality notification unit 250. If the power supply voltage V4 is outside the third voltage range, the power monitoring unit 222 outputs a signal indicating an abnormality in the power supply voltage V4 to the current control unit 240 and the abnormality notification unit 250. An abnormality in the power supply voltage V4 refers to a situation where the fourth power supply voltage V4 is either overvoltage or undervoltage. Furthermore, the signal indicating the aforementioned abnormality in the power supply voltage V4 is a low-level signal.

[0060] Here, the third voltage range is the range between the upper threshold Vth31 and the lower threshold Vth32. When the power supply voltage V4 exceeds the upper threshold Vth31, the power supply voltage V4 is considered overvoltage, and the power supply monitoring unit 222 outputs a low-level signal. Conversely, when the power supply voltage V4 is less than the lower threshold Vth32, the power supply voltage V4 is considered undervoltage, and the power supply monitoring unit 222 outputs a low-level signal. On the other hand, when the power supply voltage V4 is within the third voltage range, the power supply voltage V4 is not abnormal, and the power supply monitoring unit 222 outputs a high-level signal indicating that the power supply voltage V4 is normal. Furthermore, the aforementioned power supply monitoring units 220-222 are, for example, window comparators.

[0061] The communication unit 230 sends the sensor values ​​obtained by the calculation unit 130 of the sensor module 100 to the current control unit 240. The communication unit 230 isolates the calculation unit 130 from the current control unit 240 and enables communication from the calculation unit 130 to the current control unit 240.

[0062] The current control unit 240 operates based on the power supply voltage V1, outputting a PWM signal (control signal) with a pulse width corresponding to the signal M2 output from the power supply monitoring unit 221 to the fault notification unit 250. Specifically, when the signal M2 output from the power supply monitoring unit 221 is high, the current control unit 240 outputs a PWM signal with a pulse width corresponding to the sensor value obtained from the calculation unit 130 via the communication unit 230. This PWM signal is used, for example, to output a current in the range of 4 to 20 mA from the current output unit 260 to the two transmission lines L1 and L2.

[0063] In contrast, when the signal M2 output from the power monitoring unit 221 is low (in the case of the second abnormal signal), the current control unit 240 outputs a PWM signal (second signal) with a pulse width different from the pulse width obtainable from the sensor value obtained from the calculation unit 130. This PWM signal is used to output a burn-off current (e.g., a current of 3.6mA or less or a current of 21.6mA or more) from the current output unit 260 to the two transmission lines L1 and L2.

[0064] The current control unit 240 can be a digital circuit, which may include a processor and non-volatile or volatile semiconductor memory. Examples of processors include CPUs (Central Processing Units) and MPUs (Micro Processing Units). Examples of semiconductor memories include RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable Read Only Memory), and EEPROM (Electrically Erasable Programmable Read Only Memory). Alternatively, the current control unit 240 may also be a microprocessor such as an MCU (Micro Control Unit).

[0065] The abnormality notification unit 250 includes a clock signal generation unit 251, a pulse signal generation unit 252, and a signal selection unit 253. It switches the signal output to the current output unit 260 based on the signal M1 output from the power monitoring unit 220 and the signal M2 output from the power monitoring unit 221. Specifically, the abnormality notification unit 250 outputs the clock signal CLK output from the clock signal generation unit 251, the pulse signal P output from the pulse signal generation unit 252, or the PWM signal output from the current control unit 240 to the current output unit 260 based on signals M1 and M2.

[0066] The clock signal generation unit 251 generates a clock signal CLK (third signal) required for the operation of the current control unit 240. The pulse width of this clock signal CLK is set to a duty cycle of, for example, 50%. That is, the pulse width of the clock signal CLK is set such that if the clock signal CLK is supplied to the current output unit 260, an intermediate current (12mA) in the range of, for example, 4 to 20mA flows. In addition, this intermediate current is the current required for the start-up of the field device 1 (start-up current). The clock signal generation unit 251 outputs the generated clock signal CLK to the signal selection unit 253 and the current control unit 240.

[0067] The pulse signal generation unit 252 includes, for example, an oscillation circuit that generates a pulse signal P (first signal) with a pulse width (duty cycle) different from the clock signal CLK. For example, in order to output the aforementioned burn-out current from the current output unit 260 to the two transmission lines L1 and L2, the pulse signal generation unit 252 generates a pulse signal P with the same pulse width as the PWM signal output from the current control unit 240. That is, the pulse signal generation unit 252 outputs a pulse signal P with a pulse width different from the pulse width obtainable in the current control unit 240 based on the sensor value obtained from the calculation unit 130. The pulse signal generation unit 252 outputs the generated pulse signal P to the signal selection unit 253.

[0068] The signal selection unit 253 selects the signal to be output to the current output unit 260 from the clock signal CLK, the pulse signal P, and the PWM signal (output from the current control unit 240) based on signals M1 and M2. Specifically, the signal selection unit 253 selects the PWM signal when signal M1 is high. The signal selection unit 253 selects the pulse signal P when signal M1 is low and signal M2 is high. The signal selection unit 253 selects the clock signal CLK when both signals M1 and M2 are low.

[0069] Specifically, the signal selection unit 253 includes an OR gate 254, a first selector 255, and a second selector 256. The OR gate 254 calculates the logical sum of the signal M1 output from the power monitoring unit 220 and the signal M2 output from the power monitoring unit 221. Based on the calculation result of the OR gate 254 (hereinafter referred to as "selection signal SL1"), the first selector 255 selects either the clock signal CLK or the pulse signal P. Specifically, the first selector 255 selects the pulse signal P when the selection signal SL1 is high, and selects the clock signal CLK when the selection signal SL1 is low.

[0070] The second selector 256 selects either the signal selected by the first selector 255 or the PWM signal from the current control unit 240 based on the signal M1 output from the power monitoring unit 220 (hereinafter referred to as "selection signal SL2"). The second selector 256 selects the PWM signal when the selection signal SL2 is high, and selects the signal selected by the first selector 255 when the selection signal SL2 is low. The signal selected by the second selector 256 is input to the current output unit 260.

[0071] The current output unit 260 outputs a current (hereinafter referred to as the current signal Iout) corresponding to the signal selected by the second selector 256 to the two transmission lines L1 and L2. Specifically, the current output unit 260 outputs a current signal Iout corresponding to the pulse width (duty cycle) of the signal selected by the second selector 256. For example, when the signal selected by the second selector 256 is a PWM signal output from the current control unit 240 and has a pulse width corresponding to the sensor value obtained from the calculation unit 130, the current output unit 260 outputs a current signal Iout in the range of 4 to 20 mA.

[0072] Furthermore, for example, when the signal selected by the second selector 256 is a PWM signal output from the current control unit 240 and has a pulse width different from the pulse width obtainable from the sensor value obtained from the calculation unit 130, the current output unit 260 outputs the burn-out current (e.g., a current of 3.6mA or less or a current of 21.6mA or more) as the current signal Iout. Similarly, when the signal selected by the second selector 256 is a pulse signal P, the current output unit 260 also outputs the burn-out current as the current signal Iout. Furthermore, when the signal selected by the second selector 256 is a clock signal CLK, the current output unit 260 outputs an intermediate current (12mA) in the range of 4 to 20mA as the current signal Iout.

[0073] <Action of field equipment>

[0074] Next, the operation of the field device 1 according to the first embodiment of the present invention will be described. Hereinafter, the operation of the field device 1 when it is started (operation during startup), the operation when the power supply voltage V1 and the power supply voltage V2 are normal (stabilization operation), the operation when the power supply voltage V1 is abnormal (operation when the power supply voltage V1 is abnormal), and the operation when the power supply voltage V2 is abnormal (operation when the power supply voltage V2 is abnormal) will be described in sequence. Figure 2 This is a timing diagram of various signals of the field device according to the first embodiment of the present invention. Figure 3 This is a diagram showing the status of various signals of the field device according to the first embodiment of the present invention.

[0075] Actions during startup

[0076] Figure 2 The period T1 shown is the period during which the field device 1 is started. For example... Figure 2 As shown, immediately after the power supply to field device 1 is turned on, both power supply voltages V1 and V2 are low. Therefore, as Figure 3 As shown, signals M1 and M2 are both low-level signals, and selection signals SL1 and SL2 are both low-level signals. Therefore, the first selector 255 selects the clock signal CLK and outputs it to the second selector 256. Furthermore, since selection signal SL2 is low, the second selector 256 selects the clock signal CLK output from the first selector 255 and outputs it to the current output section 260. As a result, the current output section 260 outputs the startup current (e.g., 12mA) for the field device 1. In other words, the startup current required to start the field device 1 is supplied from the external device C via two transmission lines L1 and L2. Additionally, if the power supply voltage V1 exceeds the aforementioned lower threshold Vth12 (e.g., 2.7V), the startup of the field device 1 is complete.

[0077] Stable Actions

[0078] Figure 2 The period T2 shown is the period during which field device 1 operates stably. If field device 1 completes its startup, the power supply voltage V1 falls within the first voltage range, and the power supply voltage V2 falls within the second voltage range. Therefore, as... Figure 3 As shown, signals M1 and M2 both become high-level signals, and selection signals SL1 and SL2 also become high-level signals. Here, with selection signal SL2 high-level, the second selector 256 outputs a PWM signal regardless of the output of the first selector 255. As a result, a current in the range of, for example, 4 to 20 mA, is output from the current output section 260 based on the pulse width of the PWM signal. This allows sensor values ​​to be transmitted to an external device C.

[0079] Operation under Abnormal Power Supply Voltage V1

[0080] Figure 2 The period T3 shown is the period during which the system operates when the power supply voltage V1 is abnormal. If an abnormality occurs in the power supply circuit 210, causing the power supply voltage V1 to fall below the lower threshold value Vth12, the signal M1 output from the power monitoring unit 220 becomes low. However, since the power supply circuit 211 operates normally, the signal M2 remains high. Therefore, as... Figure 3 As shown, selection signal SL1 becomes a high-level signal, and selection signal SL2 becomes a low-level signal. Therefore, the first selector 255 selects the pulse signal P and outputs it to the second selector 256. Furthermore, since selection signal SL2 is low, the second selector 256 selects the pulse signal P and outputs it to the current output section 260. As a result, a burnout current (e.g., a current of 3.6mA or less) is output from the current output section 260. Thus, it is possible to notify the external device C of an abnormal power supply voltage occurring in the field device 1. In addition, the operation when the power supply voltage V1 is abnormal is performed not only when the power supply voltage V1 is lower than the lower threshold Vth12, but also when the power supply voltage V1 exceeds the upper threshold Vth11.

[0081] Operation under Abnormal Power Supply Voltage V2

[0082] Figure 2 The period T4 shown is the period during which the system operates when the power supply voltage V2 is abnormal. If an abnormality occurs in the power supply circuit 211, causing the power supply voltage V2 to fall below the lower threshold value Vth22, the signal M2 output from the power monitoring unit 221 becomes low. However, since the power supply circuit 210 operates normally, the signal M1 remains high. Therefore, as... Figure 3 As shown, both selection signals SL1 and SL2 become high-level signals. Here, with selection signal SL2 high-level, the second selector 256 outputs a PWM signal to the current output unit 260, regardless of the output of the first selector 255. Furthermore, since signal M2 output from the power monitoring unit 221 is low-level, the current control unit 240 outputs a PWM signal with a pulse width different from the pulse width obtainable from the sensor value obtained from the calculation unit 130. As a result, the current output unit 260 outputs a burnout current (e.g., a current of 3.6mA or less). Thus, an abnormality in the power supply voltage occurring in the field device 1 can be notified to the external device C. Moreover, this abnormal operation of the power supply voltage V2 occurs not only when the power supply voltage V2 is below the lower threshold Vth22, but also when the power supply voltage V2 exceeds the upper threshold Vth21.

[0083] As described above, the field device 1 of this embodiment includes: a current control unit 240, which operates based on a power supply voltage V1 and outputs a control signal to control the current to be output to the two transmission lines L1 and L2; a current output unit 260, which operates based on a power supply voltage V2 and outputs a current corresponding to the magnitude of the control signal output from the current control unit 240 to the two transmission lines L1 and L2; and an abnormality notification unit 250, which outputs a pulse signal P to the current output unit 260 to indicate that an abnormality has occurred when the power supply voltage V1 is abnormal. Therefore, even when the power supply voltage V1 supplied to the current control unit 240 is abnormal, an abnormality can be notified to the external device C.

[0084] Furthermore, in this embodiment, the power monitoring unit 220 monitors the overvoltage and undervoltage of the power supply voltage V1 as abnormalities of power supply voltage V1, and the power monitoring unit 221 monitors the overvoltage and undervoltage of the power supply voltage V2 as abnormalities of power supply voltage V2. Therefore, not only when power supply voltages V1 and V2 are low, but also when power supply voltages V1 and V2 are overvoltages, an external device C can be notified that an abnormality has occurred in the field device 1.

[0085] [Second Implementation]

[0086] <Field Equipment>

[0087] Figure 4 This is a block diagram illustrating the essential components of the field device according to the second embodiment of the present invention. Furthermore, in Figure 4 In the middle, to and Figure 1 Structures that are identical as shown are assigned the same reference numerals. For example... Figure 4 As shown, the field device 2 in this embodiment is... Figure 1 The transmission unit 200 of the field device 1 shown is changed to the structure of the transmission unit 200A. In the event that the power supply voltage V2 drops along with the power supply voltage V1 due to a short circuit in the power supply circuit 210, this field device 2 can also notify the external device C that an abnormality has occurred in the field device 2.

[0088] In the field device 1 of the first embodiment described above, when the power supply voltages V1 and V2 are low and the signals M1 and M2 are both low-level signals, a starting current is output from the current output unit 260. Therefore, if the power supply voltage V2 decreases along with the power supply voltage V1 due to a short circuit in the power supply circuit 210, a starting current is output from the current output unit 260 instead of a burnout current, even if a power supply abnormality occurs. In the field device 2 of this embodiment, a transmission unit 200A is provided instead of the transmission unit 200 of the field device 1, and a burnout current is output when the power supply voltage V2 decreases along with the power supply voltage V1 due to a short circuit in the power supply circuit 210.

[0089] Transmission Unit 200A Figure 1 A startup circuit 300 is added to the transmission unit 200 shown, and the output of the startup circuit 300 is connected to one of the input terminals (the input terminal of signal M2) of the OR gate 254. The startup circuit 300 is a circuit with hysteresis characteristics that receives the power supply voltage V2 generated by the power supply circuit 211. The startup circuit 300 generates a high-level signal when the power supply voltage V2 exceeds the upper limit threshold Vth41, and generates a low-level signal when the power supply voltage V2 is lower than the upper limit threshold Vth42. This startup circuit 300 is, for example, a hysteresis comparator or a Schmitt trigger. In addition, the signal M2 generated by the power supply monitoring unit 221 is output to the current control unit 240.

[0090] Figure 5 This is a circuit diagram illustrating an example of the start-up circuit of a field device provided in the second embodiment of the present invention. Figure 5 The illustrated startup circuit 300 is a non-inverting hysteresis comparator. Figure 5 The startup circuit 300 shown includes a comparator 310 and resistors R1 to R3. Resistor R1 is connected to the non-inverting input of comparator 310, resistor R2 is connected between the non-inverting input and ground, and resistor R3 is connected between the non-inverting input and output of comparator 310. A reference voltage (e.g., 2.5V) is input to the inverting input of comparator 310, and a power supply voltage V2 via resistor R1 is input to the non-inverting input of comparator 310. The hysteresis width of the startup circuit 300 is determined by the values ​​of resistors R1 to R3, the reference voltage, etc.

[0091] <Action of field equipment>

[0092] Even if the power supply voltage V2 input to the non-inverting input drops, the signal output from comparator 310 will not immediately become low, but will become low after a time corresponding to the hysteresis width of startup circuit 300. Therefore, even if the power supply voltage V2 drops along with the power supply voltage V1 due to a short circuit in power supply circuit 210, the signal output from startup circuit 300 (the signal input to one input of OR gate 254) will remain high for a certain period. Thus, a burnout current can be output from current output section 260.

[0093] Furthermore, the operation of field device 2 (operation during startup, operation during stabilization, operation when power supply voltage V1 is abnormal, and operation when power supply voltage V2 is abnormal) is basically the same as that of field device 1 in the first embodiment. Therefore, detailed description is omitted here.

[0094] As described above, the difference between the field device 2 of this embodiment and the field device 1 of the first embodiment is that it is equipped with a startup circuit 300, while the basic structure is the same as that of the field device 1 of the first embodiment. Therefore, in this embodiment, even if the power supply voltage V1 supplied to the current control unit 240 is abnormal, the external device C can be notified of the abnormality. Furthermore, not only when the power supply voltages V1 and V2 are low, but also when the power supply voltages V1 and V2 are overvoltages, the external device C can be notified of the abnormality in the field device 2. In addition, in this embodiment, even if the power supply voltage V2 decreases along with the power supply voltage V1 due to a short circuit in the power supply circuit 210, a burnout current can be output from the current output unit 260.

[0095] [Third Implementation Method]

[0096] <Field Equipment>

[0097] Figure 6 This is a block diagram illustrating the essential components of the field device according to the third embodiment of the present invention. Furthermore, in Figure 6 In the middle, to and Figure 1 Structures that are identical as shown are assigned the same reference numerals. For example... Figure 6 As shown, the field device 3 in this embodiment is... Figure 1 The transmission section 200 of the field device 1 shown is changed to a transmission section 200B. This field device 3 reduces power consumption when outputting burn-out current.

[0098] In the field device 1 of the first embodiment described above, when the power supply voltages V1 and V2 are abnormal, a burnout current (e.g., a current of 3.6mA or less) is output. During the period of outputting the burnout current, the field device 1 must operate with power corresponding to the burnout current (e.g., a current of 3.6mA or less), so the situation of insufficient power also needs to be considered. In this embodiment, the field device 3 reduces the power consumption of the field device 3 by providing a transmission unit 200B instead of the transmission unit 200 of the field device 1.

[0099] Transmission Unit 200B is in Figure 1 The transmission unit 200 shown includes an additional power cut-off unit 400. In the event of an abnormality in either the power supply voltage V1 or V2, the power cut-off unit 400 cuts off the power supply to electronic components (e.g., sensor module 100) that are not required for the output of the burn-out signal. Figure 6 As shown, the power cut-off unit 400 includes an AND gate 410 and a switch 420.

[0100] AND gate 410 performs a logical AND operation between the signal M1 output from the power monitoring unit 220 and the signal H output from the current control unit 240. Signal H is a signal that, like the signal M2 output from the power monitoring unit 221, is high when the power supply voltage V2 is normal and low when the power supply voltage V2 is abnormal. Switch 420 is connected between power supply circuits 213 and 214, and becomes either on or off based on the signal from AND gate 410. Specifically, it is on when the signal from AND gate 410 is high and off when the signal from AND gate 410 is low. When switch 420 is on, it electrically connects power supply circuits 213 and 214; when switch 420 is off, it disconnects the electrical connection between power supply circuits 213 and 214.

[0101] <Action of field equipment>

[0102] When power supply circuits 210 and 211 are operating normally (e.g., during stable operation), both signal M1 output from power monitoring unit 220 and signal M2 output from power monitoring unit 221 are at a high level. Consequently, high-level signals M1 and H are input to AND gate 410, and a high-level signal is output from AND gate 410 to switch 420. This turns switch 420 on, allowing the supply of power voltage V4 from power supply circuit 213 to power supply circuit 214.

[0103] When an abnormality occurs in power supply circuit 210 while power supply circuit 211 operates normally (in the case of an abnormality in power supply voltage V1), signal M1 output from power monitoring unit 220 is at a low level, and signal M2 output from power monitoring unit 221 is at a high level. Consequently, a low-level signal M1 and a high-level signal H are input to AND gate 410, and a low-level signal is output from AND gate 410 to switch 420. As a result, switch 420 becomes open, cutting off the supply of power supply voltage V4 from power supply circuit 213 to power supply circuit 214.

[0104] In this situation, the signal M1 output from the power monitoring unit 220 is at a low level, and the signal M2 output from the power monitoring unit 221 is at a high level. Therefore, the pulse signal P output from the pulse signal generation unit 252 is input to the current output unit 260 (see reference). Figure 3 As a result, a burnout current (e.g., a current of 3.6mA or less) is output from the current output unit 260. Thus, in the event that an abnormality in the power supply voltage V1 occurring in the field device 3 is notified to the external device C, the power supply voltage V4 from the power supply circuit 213 to the power supply circuit 214 is cut off, thereby suppressing the power consumption of the field device 3.

[0105] When the power supply circuit 210 is operating normally but an abnormality occurs in the power supply circuit 211 (in the case of an abnormality in the power supply voltage V2), the signal M1 output from the power monitoring unit 220 is high, and the signal M2 output from the power monitoring unit 221 is low. Therefore, the high-level signal M1 and the low-level signal H are input to the AND gate 410, and the AND gate 410 outputs a low-level signal to the switch 420. As a result, the switch 420 becomes open, cutting off the supply of power voltage V4 from the power supply circuit 213 to the power supply circuit 214.

[0106] In this situation, signal M1 output from power monitoring unit 220 is at a high level, and signal M2 output from power monitoring unit 221 is at a low level. Therefore, current control unit 240 outputs a PWM signal with a pulse width different from the pulse width obtainable from the sensor value obtained from calculation unit 130 (see reference). Figure 3 As a result, a burnout current (e.g., a current of 3.6mA or less) is output from the current output unit 260. Thus, in the event that an abnormality in the power supply voltage V1 occurring in the field device 3 is notified to the external device C, the power supply voltage V4 from the power supply circuit 213 to the power supply circuit 214 is cut off, thereby suppressing the power consumption of the field device 3.

[0107] In the event of an abnormality in power supply circuits 210 and 211 (including during startup), both signal M1 output from power monitoring unit 220 and signal M2 output from power monitoring unit 221 are at a low level. Consequently, low-level signals M1 and H are input to AND gate 410, and a low-level signal is output from AND gate 410 to switch 420. This causes switch 420 to become open, cutting off the supply of power voltage V4 from power supply circuit 213 to power supply circuit 214.

[0108] As described above, the difference between the field device 3 of this embodiment and the field device 1 of the first embodiment is that it is equipped with a power cut-off section 400, while its basic structure is the same as that of the field device 1 of the first embodiment. Therefore, in this embodiment, even if the power supply voltage V1 supplied to the current control section 240 is abnormal, the external device C can be notified of the abnormality. Furthermore, not only when the power supply voltages V1 and V2 are low, but also when the power supply voltages V1 and V2 are overvoltages, the external device C can be notified of the abnormality in the field device 3. In addition, in this embodiment, the power consumption of the field device 3 when outputting the burn-out current can be reduced.

[0109] [Fourth Implementation Method]

[0110] <Field Equipment>

[0111] Figure 7 This is a block diagram illustrating the essential components of the field device according to the fourth embodiment of the present invention. Furthermore, in Figure 7 In the middle, to and Figure 1 Structures that are identical as shown are assigned the same reference numerals. For example... Figure 7 As shown, the field device 4 in this embodiment is to... Figure 1 The transmission unit 200 of the field device 1 shown is changed to a transmission unit 200C that is separated from the sensor module 100. In the event of an abnormal power supply voltage on the secondary side of the power supply circuit 214, this field device 4 can notify the external device C that an abnormality has occurred in the field device 4.

[0112] like Figure 7 As shown, the sensor module 100 of the field device 4 is separate from the transmission unit 200C, and they are connected via two cables L3. The transmission unit 200C is... Figure 1 The transmission unit 200 shown is modified by adding a power monitoring unit 500 and changing the current control unit 240 to a current control unit 240C. The power monitoring unit 500 (third power monitoring unit) monitors the power supply voltage V5 and stops the operation of the communication unit 230 when the power supply voltage V5 falls outside the fifth voltage range. An abnormality in the power supply voltage V5 refers to a situation where the power supply voltage V5 is overvoltage or undervoltage.

[0113] Here, the aforementioned fifth voltage range is the range between the upper threshold Vth51 and the lower threshold Vth52. If the power supply voltage V5 exceeds the upper threshold Vth51, the power supply voltage V5 is considered overvoltage, and the power monitoring unit 500 stops the operation of the communication unit 230. Furthermore, if the power supply voltage V5 is less than the lower threshold Vth52, the power supply voltage V5 is considered undervoltage, and the power monitoring unit 500 stops the operation of the communication unit 230.

[0114] Current control unit 240C in Figure 1 The current control unit 240 shown includes a function to detect the communication status of the communication unit 230. For example, the current control unit 240C uses a CRC (Cyclic Redundancy Check) function to verify whether the communication unit 230 is operating normally. If a communication error is detected in the communication unit 230, the current control unit 240C determines that the communication unit 230 is not operating normally. If the communication unit 230 is determined to be not operating normally, the current control unit 240C outputs a PWM signal (second signal) with a pulse width different from the pulse width obtainable from the sensor value obtained from the calculation unit 130.

[0115] <Action of field equipment>

[0116] When the field device 4 is located in a factory or workshop, the sensor module 100 is sometimes positioned differently from the transmission unit 200C. In this case, the transmission unit 200C is connected to the sensor module 100 via cable L3. Here, if an abnormality occurs in the power supply voltage V5, the power monitoring unit 500 stops the communication unit 230. As a result, the current control unit 240C determines that the communication unit 230 is not operating normally and outputs a PWM signal with a pulse width different from the pulse width obtainable from the sensor value obtained from the calculation unit 130. As a result, a burnout current (e.g., a current of 3.6mA or less) is output from the current output unit 260. Thus, even if there is an abnormality in the power supply voltage on the secondary side of the power supply circuit 214, it is possible to notify the external device C that an abnormality has occurred in the field device 4.

[0117] Here, in the event of an abnormality in the power supply voltage V5, the sensor module 100 can also notify the current control unit 240C of the occurrence of the abnormality via the communication unit 230. For example, if the power supply monitoring unit 500 detects an abnormality in the power supply voltage V5, the sensor module 100 can also issue a notification. However, in this case, the sensor module 100 must receive a signal indicating the presence or absence of an abnormality from the power supply monitoring unit 500 via cable L3. Depending on the length of cable L3, it can sometimes take a considerable amount of time from the occurrence of an abnormality to the notification of the abnormality to the current control unit 240C. Furthermore, cable L3 is prone to becoming a noise intrusion path. Therefore, due to this noise, it is sometimes impossible to correctly notify the sensor module of the abnormality from the power supply monitoring unit 500, and the abnormality of the power supply voltage V5 cannot be notified to the external device C.

[0118] Therefore, in the event of an abnormality in the power supply voltage supplied to the sensor module 100, the field device 4 of this embodiment generates a communication error such as interrupting communication with the communication unit 230 in an analog manner, thereby causing the communication unit 230 to stop. This allows for reliable notification of the abnormality in the power supply voltage V5 to the external device C.

[0119] As described above, the field device 4 of this embodiment is basically the same as the field device 1 of the first embodiment, except that the power monitoring unit 500 is provided and the current control unit 240 is changed to a current control unit 240C. Therefore, in this embodiment, even if the power supply voltage V1 supplied to the current control unit 240 is abnormal, the external device C can be notified of the abnormality. Furthermore, not only when the power supply voltages V1 and V2 are low, but also when the power supply voltages V1 and V2 are overvoltages, the external device C can be notified of the abnormality in the field device 4. In addition, in this embodiment, even if the power supply voltage on the secondary side of the power supply circuit 214 is abnormal, the external device C can be notified of the abnormality in the field device 4.

[0120] The field devices according to embodiments of the present invention have been described above. The present invention is not limited to the above embodiments and can be freely modified within the scope of the present invention. For example, the first to fourth embodiments described above can be appropriately combined. For example, the field device 3 of the third embodiment and the field device 4 of the fourth embodiment may also include the startup circuit 300 included in the field device 2 of the second embodiment.

[0121] Furthermore, in the above embodiment, it was stated that power supply voltage V1 is a first power supply voltage and power supply voltage V2 is a second power supply voltage. However, the second power supply voltage only needs to be different from the first power supply voltage. For example, the second power supply voltage can be a voltage higher than the first power supply voltage. As an example, the second power supply voltage can be power supply voltage V4.

[0122] Furthermore, in the above embodiments, it was described that the field devices 1 to 4 are separate from the sensor S. However, the field devices 1 to 4 may also include the sensor S. For example, the field devices 1 to 4 may also be valve devices such as vortex flow meters, temperature sensors, flow control valves or on / off valves, actuator devices such as fans or motors, or other field devices installed in the factory.

[0123] Here, the factories equipped with field devices 1 to 4 include not only industrial factories such as chemical plants, but also factories that manage and control wellheads and their surroundings in gas fields or oil fields, factories that manage and control power generation from hydropower, thermal power, or nuclear power, factories that manage and control environmental power generation from solar or wind power, and factories that manage and control water supply and drainage or dams. It should be noted that the above-mentioned factories are merely examples and are not limited to those described above.

[0124] In this specification, terms indicating direction such as "front," "back," "up," "down," "right," "left," "vertical," "horizontal," "longitudinal," "horizontal," "row," and "column" refer to these directions in the device of the present invention. Therefore, these terms in the specification of the present invention should be interpreted relative to the device of the present invention.

[0125] The term "construction" is used to describe the structure, elements, or parts of an apparatus that are configured to perform the functions of the invention.

[0126] Furthermore, the term “method plus function” in the claims should include all structures that can be utilized to perform the functions contained in the invention.

[0127] The term "unit" is used to refer to a component, unit, hardware, or part of software programmed to perform a desired function. Typical examples of hardware are devices and circuits, but are not limited to these.

[0128] The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments. Additions, omissions, substitutions, and other modifications to the structure can be made without departing from the spirit of the present invention. The present invention is not limited by the foregoing description, but only by the appended claims.

Claims

1. A field device, characterized in that... include: The current control unit operates based on the first power supply voltage and outputs a control signal that controls the current to be output to the transmission line. The current output unit operates by using a second power supply voltage that is different from the first power supply voltage, and is able to output a current corresponding to the magnitude of the control signal output from the current control unit to the transmission line. as well as In the event of an abnormality in the first power supply voltage, the abnormality notification unit will output a first signal to the current output unit, indicating that an abnormal burnout current has occurred. In the event of an abnormality in the second power supply voltage, the current control unit will output a second signal, which is used to cause the current output unit to output the burn-out current, as the control signal output.

2. The field device according to claim 1, characterized in that... Also includes: The first power supply monitoring unit outputs a first abnormality signal indicating an abnormality in the first power supply voltage when the first power supply voltage falls outside a predetermined first voltage range; and The second power supply monitoring unit outputs a second abnormality signal indicating an abnormality in the second power supply voltage when the second power supply voltage falls outside a predetermined second voltage range.

3. The field device according to claim 2, characterized in that, When the first abnormal signal is input and the second abnormal signal is not input, the abnormality notification unit outputs the first signal to the current output unit.

4. The field device according to claim 2, characterized in that, When the first abnormal signal is not input but the second abnormal signal is input, the abnormal notification unit outputs the second signal to the current output unit.

5. The field device according to claim 2, characterized in that, When the first abnormal signal and the second abnormal signal are input, the abnormality notification unit outputs a third signal to the current output unit to cause the current output unit to output a starting current, wherein the starting current is the current required to start the field device.

6. The field device according to any one of claims 2 to 5, characterized in that, It also includes a startup circuit that delays the input of the second abnormal signal to the abnormal notification unit for a certain period of time.

7. The field device according to any one of claims 1 to 5, characterized in that, It also includes a sensor module that operates via a third power supply voltage different from the first and second power supply voltages, and outputs a sensor value representing the sensor's measurement result. The current control unit outputs a PWM signal having a pulse width corresponding to the sensor value output from the sensor module as the control signal. The current output section outputs a current corresponding to the pulse width of the PWM signal to the transmission line.

8. The field device according to claim 7, characterized in that, The first signal and the second signal are signals having pulse widths that are different from the pulse widths obtainable from the sensor values ​​output from the sensor module.

9. The field device according to claim 7, characterized in that... Also includes: The communication unit performs communication between the sensor module and the current control unit; as well as The third power supply monitoring unit stops the operation of the communication unit if the third power supply voltage is abnormal. The current control unit outputs the second signal when the communication unit stops operating.

10. The field device according to claim 7, characterized in that, It also includes a power cut-off unit, which, in the event of an abnormality in the first power supply voltage or the second power supply voltage, cuts off at least the supply of the third power supply voltage to the sensor module.

11. The field device according to claim 5, characterized in that, The anomaly notification unit includes: A pulse signal generation unit that generates pulse signals; and The clock signal generation unit that generates clock signals. The first signal is the pulse signal generated by the pulse signal generation unit. The third signal is the clock signal generated by the clock signal generation unit.

12. The field device according to claim 11, characterized in that, The abnormality notification unit includes a first selector, which selects either the pulse signal generated by the pulse signal generation unit or the clock signal generated by the clock signal generation unit.

13. The field device according to claim 12, characterized in that, The first selector selects the clock signal generated by the clock signal generation unit when both the first abnormal signal and the second abnormal signal are input, and selects the pulse signal generated by the pulse signal generation unit when the other abnormal signals are input.

14. The field device according to claim 12, characterized in that, It also includes a sensor module that operates via a third power supply voltage different from the first and second power supply voltages, and outputs a sensor value representing the sensor's measurement result. The current control unit outputs a PWM signal having a pulse width corresponding to the sensor value output from the sensor module as the control signal. The abnormality notification unit further includes a second selector, which selects either the signal selected by the first selector or the PWM signal output from the current control unit.

15. The field device according to claim 6, characterized in that, The startup circuit is a hysteresis comparator or a Schmitt trigger.

16. The field device according to claim 9, characterized in that, It also includes a transmission unit, which comprises the current control unit, the current output unit, and the abnormality notification unit. The transmission unit is detached from the sensor module and connected to the sensor module via a cable. The sensor module outputs the sensor value to the communication unit via the cable.

17. The field device according to claim 10, characterized in that, The power cut-off section includes a switch, which is in a conducting state when the first power supply voltage and the second power supply voltage are normal, and in a disconnected state when at least one of the first power supply voltage or the second power supply voltage is abnormal.

18. The field device according to claim 17, characterized in that, When the switch is in the ON state, the third power supply voltage is supplied to the sensor module. When the switch is in the open state, the power cut-off section cuts off the supply of the third power supply voltage to the sensor module.

19. A field device, characterized in that... include: The current control unit operates based on the first power supply voltage and outputs a control signal that controls the current to be output to the transmission line. The current output unit operates by using a second power supply voltage that is different from the first power supply voltage, and is able to output a current corresponding to the magnitude of the control signal output from the current control unit to the transmission line. The abnormality notification unit outputs a first signal to the current output unit to indicate that an abnormal burnout current has occurred when the first power supply voltage is abnormal. The first power supply circuit generates the first power supply voltage by stepping down the second power supply voltage. as well as The second power supply circuit generates the second power supply voltage based on the power supplied from the external device.

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