JP2018201309A - Noise countermeasure circuit and field apparatus - Google Patents

Abstract

To execute a noise countermeasure without modifying and replacing a field apparatus and a power supply.SOLUTION: A noise countermeasure circuit 11 is provided with: a first capacity adjustment part 12-1 which is inserted between a + power line L1 and a ground A and in which a switch SW1 is connected with a capacitor C1 in series; and a second capacity adjustment part 12-2 which is inserted between a - power line L2 and the ground A and in which a switch SW2 is connected with a capacitor C2 in series.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a noise countermeasure circuit and a field device.

  Field devices used in the industrial market, such as valve positioners and pressure transmitters, are often used in environments where there is a noise source between the power source and the field device. For example, ground (ground) is usually treated as the same potential everywhere, but in reality, the electrical resistance component between two points increases as the distance increases. When the resistance component increases, when the power supply and the field device are installed at some distance, a potential difference or noise is generated between the ground at the power source and the ground at the field device, affecting the operation of the field device. Sometimes. Further, when the cable between the power source and the field device is wired in parallel with the other cable, noise from the other cable may be superimposed on the cable between the power source and the field device due to capacitive coupling between the cables.

  As shown in FIG. 11, in the conventional field device 100, capacitors C100 and C101 are connected between the + (plus) power line L1 and the ground A and between the-(minus) power line L2 and the ground A as countermeasures against various noises. ing. When there is a noise source between the power supply and the field device, the influence of noise varies depending on the circuit configuration of the power supply and the field device and the state of the cable. In particular, since noise acts as an alternating current component, what kind of capacitive component each power supply and field device have with respect to the ground is an important issue.

  However, since there is no particular rule regarding the capacity component of the power supply or each field device with respect to the ground, when any power source or field device of various manufacturers is connected at the site, what kind of capacity these combinations have with respect to the ground? I don't know if it will form an ingredient. For this reason, it is difficult to realize noise countermeasures that are optimal for all sites with the circuit configuration shown in FIG. 11, and in some cases, a noise path that is undesirable for field devices is formed and affected by noise. (See Patent Document 1).

  A conventional problem will be described with reference to FIG. Here, a case where the power source line L2 is grounded to the ground A2 in the power source 200 will be described. In the example of FIG. 12, a noise source N caused by, for example, a resistance component exists between the power supply side ground A2 and the field device side ground A1.

  When the setting of the capacitors C100 and C101 is not appropriate, considering the path of the noise voltage with reference to the power supply side ground A2, the noise voltage is transmitted via the field device side ground A1 and the capacitor C100 for the + power supply line L1. It becomes a state. On the other hand, the -power supply line L2 has the same potential as the power supply side ground A2. In this state, a noise potential difference is generated between the + power supply line L1 and the −power supply line L2 of the field device 100, and the noise current passes through the internal circuit 101 of the field device 100 through the path 300 shown in FIG. Will affect the circuit operation.

  When the operation of the field device 100 is affected by noise, it is necessary to take measures such as changing the power source 200 or the circuit of the field device 100 so that the capacity is set optimally on the spot.

Japanese Unexamined Patent Publication No. 2017-020631

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a noise countermeasure circuit and a field device that can implement noise countermeasures without modifying or replacing field devices or power supplies. .

The noise countermeasure circuit of the present invention (first to fourth embodiments) is configured to be inserted between a power supply line for supplying a power supply voltage from a power supply to an internal circuit of a field device and the ground, and the capacity can be adjusted. It is characterized by comprising a capacity adjusting unit.
Further, in one configuration example (first and third embodiments) of the noise countermeasure circuit of the present invention, the capacitance adjusting unit includes a switch inserted between the power supply line and the ground, and the same row as the switch. A capacitor inserted between the power line and the ground and connected directly or indirectly to the switch, the capacitance being adjustable by turning the switch on and off. Is.
Moreover, in one configuration example (first and third embodiments) of the noise countermeasure circuit of the present invention, the capacitance adjusting unit includes a plurality of circuits including the switch and the capacitor per power supply line. It is what.
Moreover, in one configuration example (second and fourth embodiments) of the noise countermeasure circuit of the present invention, the capacitance adjusting unit is composed of a variable capacitor.
In one configuration example (first to fourth embodiments) of the noise countermeasure circuit according to the present invention, the capacitance adjusting unit supplies the first power supply voltage to the internal circuit of the field device. A first capacity adjusting unit inserted between a line and the ground, and a second power supply line for supplying a second power supply voltage to an internal circuit of the field device, and the ground. And a second capacity adjustment unit.

Also, one configuration example (third and fourth embodiments) of the noise countermeasure circuit of the present invention measures the first AC potential difference between the first power supply line and the second power supply line. A first measuring unit configured to measure, a second measuring unit configured to measure a second AC potential difference between the first power line and the ground, and the second power line A third measuring unit configured to measure a third AC potential difference between the first AC potential difference and the ground, a magnitude determination between the first AC potential difference and a reference value, and the second AC potential difference and the A determination unit configured to determine the magnitude of the third AC potential difference, and a control unit configured to adjust the capacities of the first and second capacity adjustment units according to the determination result of the determination unit Are further provided.
Further, in one configuration example (third and fourth embodiments) of the noise countermeasure circuit of the present invention, the control unit determines whether the second AC potential difference is greater than or equal to the reference value. And the capacitance of the first and second capacitance adjusting units is adjusted in a direction in which the first AC potential difference is reduced based on the result of the magnitude determination of the third AC potential difference. .
Further, in one configuration example (third and fourth embodiments) of the noise countermeasure circuit of the present invention, the control unit is configured such that the first AC potential difference is equal to or greater than the reference value, and the second AC When the potential difference is smaller than the third AC potential difference, the capacitance of the first capacitance adjustment unit is adjusted in a decreasing direction, the first AC potential difference is greater than or equal to the reference value, and the second When the AC potential difference is larger than the third AC potential difference, adjustment is performed in a direction in which the capacity of the second capacity adjustment unit decreases.
The field device (first to fourth embodiments) of the present invention includes the noise countermeasure circuit.

  According to the present invention, by inserting a capacity adjustment unit between a power supply line that supplies a power supply voltage from a power supply to an internal circuit of the field device and the ground, the power supply line of the field device can be connected at the site where the field device is installed. The noise path can be adjusted by setting the capacitance of the capacitance adjustment unit so that the capacitance component possessed with respect to the ground is appropriate, and noise countermeasures should be implemented without modifying or replacing field devices or power supplies Can do.

  In the present invention, the first, second, and third measurement units, the determination unit, and the control unit are provided, so that the capacity component that the power line of the field device has against the ground at the site where the field device is installed. Therefore, the capacity of the capacity adjustment unit can be automatically optimized so that appropriate noise countermeasures can be automatically taken.

FIG. 1 is a circuit diagram showing a configuration of a field device according to a first embodiment of the present invention. FIG. 2 is a diagram for explaining the effect of the noise countermeasure circuit according to the first embodiment of the present invention. FIG. 3 is a circuit diagram showing another configuration of the field device according to the first embodiment of the present invention. FIG. 4 is a circuit diagram showing a configuration of a field device according to the second embodiment of the present invention. FIG. 5 is a circuit diagram showing the configuration of a field device according to the third embodiment of the present invention. FIG. 6 is a flowchart for explaining the operation of the noise countermeasure circuit according to the third embodiment of the present invention. FIG. 7 is a circuit diagram showing another configuration of the field device according to the third embodiment of the present invention. FIG. 8 is a flowchart for explaining another operation of the noise countermeasure circuit according to the third example of the present invention. FIG. 9 is a circuit diagram showing a configuration of a field device according to the fourth embodiment of the present invention. FIG. 10 is a flowchart for explaining the operation of the noise countermeasure circuit according to the fourth embodiment of the present invention. FIG. 11 is a circuit diagram illustrating a configuration of a conventional noise countermeasure circuit. FIG. 12 is a diagram for explaining a problem of the conventional noise countermeasure circuit.

[First embodiment]
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a configuration of a field device according to a first embodiment of the present invention. The field device 1 includes an internal circuit 10 that implements various functions and a noise countermeasure circuit 11.

  The internal circuit 10 controls, for example, the opening of the valve (when the field device 1 is a valve positioner) or measures the pressure difference between two points or the absolute pressure (when the field device 1 is a pressure transmitter). ). Needless to say, the field device 1 is not limited to a valve positioner or a pressure transmitter.

  The noise countermeasure circuit 11 supplies a positive power supply voltage from a power supply (not shown) to the internal circuit 10 of the field device 1 + a capacitor C1 inserted between the power supply line L1 (first power supply line) and the ground A, A negative power supply voltage (for example, ground potential) is supplied from the power supply to the internal circuit 10-the capacitor C2 inserted between the power supply line L2 (second power supply line) and the ground A, the + power supply line L1 and the ground A And a switch SW1 inserted in series with the capacitor C1, and a switch SW2 inserted in series with the capacitor C2 between the power line L2 and the ground A.

  As described above, in this embodiment, the first capacitance adjusting unit 12-1 in which the switch SW1 and the capacitor C1 are connected in series is inserted between the + power supply line L1 and the ground A, and the − power supply line L2 Between the ground A, a second capacitance adjusting unit 12-2 in which a switch SW2 and a capacitor C2 are connected in series is inserted.

  As a result, in this embodiment, the switches SW1 and SW2 are turned on / off so that the capacity component of the power supply lines L1 and L2 of the field device 1 with respect to the ground A is appropriate at the site where the field device 1 is installed. The noise path can be adjusted by setting and adjusting the capacity of the capacity adjusting units 12-1 and 12-2, and noise countermeasures can be implemented without modifying or replacing the field device 1 or the power source. .

  The effect of the present embodiment will be described with reference to FIG. Here, a case where the negative power supply line L2 is grounded to the ground A2 in the power supply 2 will be described. As in the prior art, in the example of FIG. 2, there is a noise source N due to, for example, a resistance component between the power supply side ground A2 and the field device side ground A1.

  When the switch SW1 of the noise countermeasure circuit 11 is set to OFF and the switch SW2 is set to ON, considering the path of the noise voltage with reference to the power supply side ground A2, the switch SW1 is set to OFF. Since the noise path 3 through the side ground A1 and the capacitor C1 is blocked, no noise voltage is transmitted to the + power supply line L1. On the other hand, the -power supply line L2 has the same potential as the power supply side ground A2. In this state, a noise potential difference does not occur between the + power supply line L1 and the −power supply line L2 of the field device 1, so that a conventional noise current does not flow through the internal circuit 10. Thus, in this embodiment, noise countermeasures can be implemented by appropriately setting ON / OFF of the switches SW1 and SW2.

  In FIG. 1 and FIG. 2, the circuit in which the switch and the capacitor are connected in series is one per power line. However, the circuit is not limited to this, and the switch and the capacitor are connected in series as shown in FIG. A plurality of circuits may be provided per power line. A circuit in which a plurality of circuits in which a switch SW1 and a capacitor C1 are connected in series is arranged in parallel between the + power supply line L1 and the ground A constitutes a first capacitance adjusting unit 12-1a. Further, a circuit in which a plurality of circuits in which a switch SW2 and a capacitor C2 are connected in series is arranged in parallel between the power source line L2 and the ground A constitutes a second capacitance adjusting unit 12-2a.

  According to the noise countermeasure circuit 11a of the field device 1a shown in FIG. 3, the capacity of the power supply lines L1 and L2 of the field device 1a with respect to the ground A can be finely adjusted, and more appropriate noise countermeasures are implemented. It becomes possible.

  The switches SW1 and SW2 may be ones that can be set ON / OFF by a mechanical operation, or may be ones that can be set ON / OFF by an external control signal.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. FIG. 4 is a circuit diagram showing the configuration of a field device according to the second embodiment of the present invention. The same components as those in FIGS. 1 and 3 are given the same reference numerals. The field device 1b of this embodiment includes an internal circuit 10 and a noise countermeasure circuit 11b.

  The noise countermeasure circuit 11b includes a variable capacitor C3 inserted between the + power supply line L1 and the ground A, and a variable capacitor C4 inserted between the −power supply line L2 and the ground A. The variable capacitor C3 constitutes a first capacitance adjustment unit 12-1b, and the variable capacitor C4 constitutes a second capacitance adjustment unit 12-1b.

  As described above, in this embodiment, by using the variable capacitors C3 and C4 instead of the circuit in which the switch and the capacitor are connected in series, the capacity of the power supply lines L1 and L2 of the field device 1 with respect to the ground A is increased. It is possible to adjust continuously, and it is possible to implement more appropriate noise countermeasures.

  The variable capacitors C3 and C4 may be those whose capacitance is changed by a mechanical operation, or may be one whose capacitance is changed by a control signal from the outside.

[Third embodiment]
Next, a third embodiment of the present invention will be described. FIG. 5 is a circuit diagram showing the configuration of a field device according to the third embodiment of the present invention. The same components as those in FIGS. 1, 3, and 4 are given the same reference numerals. The field device 1c of this embodiment includes an internal circuit 10 and a noise countermeasure circuit 11c. In the first embodiment, an operator who takes measures against noise at the installation location of the field device needs to determine ON / OFF setting of the switches SW1 and SW2 by trial and error. On the other hand, the present embodiment automatically optimizes the ON / OFF setting of the switches SW1 and SW2.

  The noise countermeasure circuit 11c includes capacitors C1 and C2, switches SW1 and SW2, a measurement unit 110 that measures an AC potential difference (first AC potential difference) between the + power supply line L1 and the −power supply line L2, and a + power supply. A measurement unit 111 that measures an AC potential difference (second AC potential difference) between the line L1 and the ground A, and a measurement that measures an AC potential difference (third AC potential difference) between the power line L2 and the ground A. Unit 112, determination unit 113 for determining the magnitude of the measurement result of the measurement unit 110 and the reference value, and determination of the magnitude of the measurement result of the measurement units 111 and 112, and switches SW1 and SW2 according to the determination result of the determination unit 113 And a control unit 114 that adjusts the capacity by controlling ON / OFF of the. In this embodiment, switches SW1 and SW2 that can be set ON / OFF by a control signal from the control unit 114 are used.

  FIG. 6 is a flowchart for explaining the operation of the noise countermeasure circuit 11c of this embodiment. In the initial state, the control unit 114 turns on both the switches SW1 and SW2. The measurement unit 110 measures the AC potential difference V12 between the + power supply line L1 and the −power supply line L2 (step S1 in FIG. 6). Measurement unit 111 measures AC potential difference V1 between + power supply line L1 and ground A (step S2 in FIG. 6). The measuring unit 112 measures the AC potential difference V2 between the power line L2 and the ground A (step S3 in FIG. 6). Measurement units 110 to 112 may detect peak values of AC potential differences V12, V1, and V2, or may detect average values.

  Subsequently, the determination unit 113 determines the magnitude of the AC potential difference V12 measured by the measurement unit 110 and a predetermined reference value Vref. Determination unit 113 determines that internal circuit 10 is not likely to be affected by noise when | V12 | <Vref, that is, when the absolute value of AC potential difference V12 is smaller than reference value Vref (YES in step S4 in FIG. 6). To do. When the absolute value of the AC potential difference V12 is smaller than the reference value Vref, the control unit 114 maintains the current state of the switches SW1 and SW2 (here, both are ON) and ends the process.

  The reference value Vref is determined by, for example, experimentally creating a situation in which the internal circuit 10 transitions from a state that is not affected by noise to a state that is affected by noise, and an alternating current when the state of the internal circuit 10 changes. The absolute value of the potential difference V12 may be set as the reference value Vref.

  Determination unit 113 determines that internal circuit 10 may be affected by noise when the absolute value of AC potential difference V12 is greater than or equal to reference value Vref (YES in step S4), and determines the AC measured by measurement unit 111. The magnitude difference between the potential difference V1 and the AC potential difference V2 measured by the measuring unit 112 is determined. The AC potential difference V1 corresponds to the voltage across the capacitor C1, and the AC potential difference V2 corresponds to the voltage across the capacitor C2.

  Determination unit 113 determines that | V1 | <| V2 |, that is, if the absolute value of AC potential difference V1 is smaller than the absolute value of AC potential difference V2 (YES in step S5 in FIG. 6), field device-side ground A1 and capacitor C1. Through the + power supply line L1 is determined to be a noise path. That is, the noise voltage is applied to the internal circuit 10 as much as the AC potential difference V1 is small. When the absolute value of the AC potential difference V1 is smaller than the absolute value of the AC potential difference V2, the control unit 114 switches the switch SW1 from ON to OFF and maintains the current state of the switch SW2 (here, ON) (FIG. 6). Step S6), the process ends.

  Determination unit 113 determines that | V1 |> | V2 |, that is, if the absolute value of AC potential difference V1 is larger than the absolute value of AC potential difference V2 (NO in step S5), via field device-side ground A1 and capacitor C2. -It is determined that the route to the power supply line L2 is a noise route. That is, the noise voltage is applied to the internal circuit 10 as much as the AC potential difference V2 is small. When the absolute value of the AC potential difference V1 is larger than the absolute value of the AC potential difference V2, the control unit 114 maintains the current state of the switch SW1 (here, ON) and switches the switch SW2 from ON to OFF (FIG. 6). Step S7) and the process is terminated. The operations of the determination unit 113 and the control unit 114 are shown in Table 1.

  As described above, in this embodiment, the switches SW1 and SW2 are turned on / off so that the capacity component of the power supply lines L1 and L2 of the field device 1c with respect to the ground A is appropriate at the site where the field device 1c is installed. OFF can be automatically optimized, and appropriate noise countermeasures can be automatically implemented.

  The present embodiment may be applied to a configuration in which a plurality of circuits each having a switch and a capacitor connected in series are provided per power supply line. The configuration of the field device 1d in this case is shown in FIG. 7, and the operation of the noise countermeasure circuit 11d is shown in FIG. The processes in steps S1 to S4 in FIG. 8 are as described above.

  The determination unit 113d of the noise countermeasure circuit 11d performs the magnitude determination between the AC potential difference V12 and the reference value Vref as described above (step S4 in FIG. 8). When the absolute value of the AC potential difference V12 is greater than or equal to the reference value Vref, the AC potential difference V1. And the processing according to the magnitude determination between the AC potential difference V2 are performed as described above (steps S5 to S7 in FIG. 8). And the determination part 113d acquires the measurement result of the measurement parts 110-112 again after the process of step S5-S7 (FIG. 8 step S8-S10), and the absolute value of alternating current potential difference V12 becomes smaller than the reference value Vref. The process of steps S5 to S7 is performed until there is no switch that can be changed from the ON state to the OFF state on the side of the switch whose state is to be changed (NO in step S12 in FIG. 8). Run repeatedly.

  For example, after the one of the plurality of switches SW1 is changed from the ON state to the OFF state by the control unit 114d (Step S6), the determination unit 113d has the absolute value of the latest AC potential difference V12 still greater than or equal to the reference value Vref ( If NO in step S11), if there are any switches in the ON state among the plurality of switches SW1 (YES in step S12), the process returns to step S5. The determination unit 113d determines that the absolute value of the latest AC potential difference V12 is still greater than or equal to the reference value Vref after one of the plurality of switches SW2 is changed from the ON state to the OFF state by the control unit 114d (step S7). (NO in step S11) If there are any switches in the ON state among the plurality of switches SW2 (YES in step S12), the process returns to step S5.

  Thus, ON / OFF of the plurality of switches SW1 and SW2 is automatically performed in a direction in which the absolute value of the AC potential difference V12 decreases (so that the absolute value of the AC potential difference V1 and the absolute value of the AC potential difference V2 are equal). Therefore, it is possible to implement more appropriate noise countermeasures.

[Fourth embodiment]
Next, a fourth embodiment of the present invention will be described. FIG. 9 is a circuit diagram showing the configuration of a field device according to the fourth embodiment of the present invention. The same components as those in FIGS. 1, 3 to 5 and 7 are denoted by the same reference numerals. The field device 1e of this embodiment includes an internal circuit 10 and a noise countermeasure circuit 11e. In the second embodiment, a worker who takes measures against noise at the installation location of the field device needs to determine the capacities of the variable capacitors C3 and C4 by trial and error. On the other hand, the present embodiment automatically optimizes the capacitances of the variable capacitors C3 and C4.

  The noise countermeasure circuit 11e includes variable capacitors C3 and C4, measurement units 110 to 112, a determination unit 113e, and a control unit 114e that adjusts the capacitance of the variable capacitors C3 and C4 according to the determination result of the determination unit 113e. Is done. In the present embodiment, as the variable capacitors C3 and C4, capacitors whose capacity can be changed by a control signal from the control unit 114e are used.

FIG. 10 is a flowchart for explaining the operation of the noise countermeasure circuit 11e of this embodiment. The processing in steps S1 to S5 in FIG. 10 is as described in the third embodiment.
When the absolute value of AC potential difference V1 is smaller than the absolute value of AC potential difference V2 (YES in step S5 in FIG. 10), control unit 114e performs control so that the capacitance of variable capacitor C3 is reduced by a predetermined amount, and variable capacitor C4. Is maintained (step S13 in FIG. 10).

  In addition, when the absolute value of AC potential difference V1 is larger than the absolute value of AC potential difference V2 (NO in step S5), control unit 114e performs control so that the capacity of variable capacitor C4 is reduced by a predetermined amount, and variable capacitor C3. Is maintained (step S14 in FIG. 10).

  The determination unit 113e acquires the measurement results of the measurement units 110 to 112 again after the processes of steps S5, S13, and S14 (steps S15 to S17 in FIG. 10), and the absolute value of the AC potential difference V12 is smaller than the reference value Vref. Until the capacity of the variable capacitor to be changed reaches the lower limit and cannot be changed (NO in step S19 of FIG. 10), the processes of steps S5, S13, and S14 are repeatedly executed. .

  For example, after the capacity of the variable capacitor C3 is reduced by the control unit 114e (step S13), the determination unit 113e has the absolute value of the latest AC potential difference V12 still greater than or equal to the reference value Vref (NO in step S18), and the variable capacitor C3 If it is possible to further reduce the capacity of the control signal (the control signal can be changed in the direction of reducing the capacity of C3) (YES in step S19), the process returns to step S5. In addition, after the capacity of the variable capacitor C4 is reduced by the control unit 114e (step S14), the determination unit 113e determines that the absolute value of the latest AC potential difference V12 is still greater than or equal to the reference value Vref (NO in step S18). If the capacity of C4 can be further reduced (the control signal can be changed in the direction of reducing the capacity of C4) (YES in step S19), the process returns to step S5.

  In this way, the capacitances of the variable capacitors C3 and C4 are automatically optimized so that the absolute value of the AC potential difference V12 decreases (so that the absolute value of the AC potential difference V1 and the absolute value of the AC potential difference V2 are equal). This makes it possible to implement more appropriate noise countermeasures. Table 2 shows operations of the determination unit 113e and the control unit 114e.

  6, 8, and 10 may be performed once, for example, when the field devices 1c, 1d, and 1e are turned on, or may be performed at regular intervals. However, it may be carried out when there is an instruction from the worker.

  The determination units 113, 113d, and 113e described in the third and fourth embodiments are realized by, for example, a computer having a CPU (Central Processing Unit), a storage device, and an interface, and a program that controls these hardware resources. be able to. The CPU executes the processing described in the third and fourth embodiments according to the program stored in the storage device.

  In the first to fourth embodiments, the noise countermeasure circuits 11, 11a to 11e are provided in the field devices 1, 1a to 1e. However, the present invention is not limited to this, and the noise countermeasure circuits 11, 11a to 11e are provided in the field. You may make it provide in the exterior of apparatus 1,1a-1e. However, in order to avoid an increase in the distance between the ground of the noise countermeasure circuits 11, 11a to 11e and the ground of the field equipment 1, 1a to 1e, the noise countermeasure circuits 11, 11a to 11e are connected to the field equipment 1, It is desirable to provide in the vicinity of 1a-1e.

  In the first and third embodiments, a circuit in which the switch SW1 and the capacitor C1 are directly connected is referred to as the first capacitance adjusting unit 12-1, and a circuit in which the switch SW2 and the capacitor C2 are directly connected is the first. However, the capacity adjustment units 12-1 and 12-2 are not limited to such a configuration. For example, an element or a circuit such as a resistor may be inserted between the switch SW1 and the capacitor C1 and between the switch SW2 and the capacitor C2. That is, the capacitors C1 and C2 may be inserted between the power supply line and the ground in the same row as the switches SW1 and SW2, respectively, and may be directly or indirectly connected to the switches SW1 and SW2.

  In the first capacitance adjusting unit 12-1a shown in FIGS. 3 and 7, a plurality of circuits including the switch SW1 and the capacitor C1 may be provided for each power supply line, and each capacitor C1 is a switch in the same row. It may be connected directly or indirectly to SW1. Similarly, in the second capacitance adjusting unit 12-2a, a plurality of circuits including the switch SW2 and the capacitor C2 may be provided per power supply line, and each capacitor C2 may be directly or directly connected to the switch SW2 in the same row. It only needs to be connected indirectly.

  The present invention can be applied to noise countermeasures for field devices.

  DESCRIPTION OF SYMBOLS 1,1a-1e ... Field device, 10 ... Internal circuit, 11, 11a-11e ... Noise countermeasure circuit, 12-1, 12-1a, 12-1b, 12-2, 12-2a, 12-1b ... Capacity adjustment , 110 to 112 ... measurement unit, 113, 113d, 113e ... determination unit, 114, 114d, 114e ... control unit, L1, L2 ... power line, A ... ground, C1, C2 ... capacitor, C3, C4 ... variable capacitor , SW1, SW2 ... switches.

Claims (9)

  A noise countermeasure circuit comprising: a capacity adjustment unit that is inserted between a power supply line for supplying a power supply voltage from a power supply to an internal circuit of a field device and a ground, and configured to adjust the capacity. The noise countermeasure circuit according to claim 1,
The capacity adjusting unit is
A switch inserted between the power line and the ground;
A capacitor inserted between the power line and the ground in the same row as the switch, and a capacitor connected directly or indirectly to the switch;
A noise countermeasure circuit characterized in that the capacitance can be adjusted by turning on and off the switch. The noise suppression circuit according to claim 2,
The noise countermeasure circuit, wherein the capacitance adjusting unit includes a plurality of circuits including the switch and the capacitor per power line. The noise countermeasure circuit according to claim 1,
The noise countermeasure circuit, wherein the capacitance adjusting unit is composed of a variable capacitor. The noise suppression circuit according to any one of claims 1 to 4,
The capacity adjusting unit includes a first capacity adjusting unit inserted between the first power supply line for supplying a first power supply voltage to an internal circuit of the field device and the ground, and an inside of the field device. A noise countermeasure circuit comprising: a second capacitance adjusting unit inserted between the second power supply line for supplying a second power supply voltage to the circuit and the ground. In the noise countermeasure circuit according to claim 5,
A first measurement unit configured to measure a first AC potential difference between the first power supply line and the second power supply line;
A second measuring unit configured to measure a second AC potential difference between the first power line and the ground;
A third measuring unit configured to measure a third AC potential difference between the second power line and the ground;
A determination unit configured to determine the magnitude of the first AC potential difference and a reference value, and to determine the magnitude of the second AC potential difference and the third AC potential difference;
A noise countermeasure circuit, further comprising: a control unit configured to adjust a capacitance of the first and second capacitance adjustment units according to a determination result of the determination unit. The noise suppression circuit according to claim 6,
When the first AC potential difference is greater than or equal to the reference value, the control unit reduces the first AC potential difference based on a result of the magnitude determination between the second AC potential difference and the third AC potential difference. A noise countermeasure circuit characterized by adjusting the capacitances of the first and second capacitance adjustment units in the direction of The noise countermeasure circuit according to claim 7,
When the first AC potential difference is greater than or equal to the reference value and the second AC potential difference is smaller than the third AC potential difference, the control unit has a capacitance of the first capacitance adjustment unit. When the first AC potential difference is greater than or equal to the reference value and the second AC potential difference is greater than the third AC potential difference, the capacitance of the second capacitance adjustment unit is adjusted in a decreasing direction. A noise countermeasure circuit that adjusts in a direction that reduces noise.   A field device comprising the noise countermeasure circuit according to claim 1.

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