JP5781889B2 - Positioner - Google Patents

Description

  The present invention receives a DC current signal from a host system via a pair of electric wires, generates its own operating power supply from the DC current signal, and opens the control valve according to the value of the DC current signal. The present invention relates to a positioner for controlling the degree.

  Conventionally, this type of positioner is designed to operate with a current (DC current signal) of 4 to 20 mA sent from the host system via a pair of wires. For example, when a current of 4 mA is sent from the host system, the opening of the control valve is 0%, and when a current of 20 mA is sent, the opening of the control valve is 100%.

  In this case, since the supply current from the host system changes in the range of 4 mA (lower limit current value) to 20 mA (upper limit current value), the internal circuit of the positioner should always be secured as the current value supplied from the host system. The self-operating power supply is generated from a current of less than 4 mA possible.

  A set opening value for the control valve is input from the host system to the positioner. Further, the actual opening value of the control valve is also obtained through the opening sensor. Therefore, in the positioner, by calculating the relationship between the set opening value of the control valve and the actual opening value, it is possible to perform abnormality diagnosis of the control valve, self-diagnosis, and the like. If such an abnormality diagnosis function is provided in the positioner, it is not necessary to provide a separate abnormality diagnosis device, and the function of the system can be improved at a low cost (for example, see Patent Document 1).

  For these reasons, in addition to the original function of controlling the valve opening of the control valve, the positioner has recently received the results of the valve opening transmission function, the control valve abnormality diagnosis, and its own abnormality diagnosis. A positioner has been proposed that has a communication function that transmits information to the control valve and receives information such as control parameters for control calculation of the control valve from the host system.

  For example, in the positioner disclosed in Patent Document 2, a current signal including set value information is input via an input terminal, and a digital calculation circuit that performs control calculation of a pneumatic signal so as to match the set value, and the digital In a positioner having an electropneumatic conversion module that converts a control output of an arithmetic circuit into a pneumatic signal, power supply voltage generating means for generating an internal power supply voltage from a current signal including set value information, and the power supply voltage generating means are connected in series A variable impedance circuit and a variable impedance control circuit for controlling the impedance of the variable impedance circuit are provided, and the variable impedance circuit is connected in parallel to the electropneumatic conversion module.

  In this positioner, the variable impedance control circuit lowers the impedance of the variable impedance circuit in the low frequency region and increases the impedance of the variable impedance circuit in the high frequency region. That is, the impedance for the direct current signal is lowered, and the impedance for the alternating current signal is made higher than the impedance for the direct current signal. By using such a variable impedance circuit, it is possible to receive information (AC current signal) from the host system that is sent superimposed on the DC current signal.

JP 2004-151941 A JP 2000-304148 A

  The positioner shown in Patent Document 2 is designed to have a communication function from the beginning. In contrast, there is a demand for a positioner having only a valve opening control function that does not have a communication function (hereinafter, this positioner is referred to as a conventional positioner) to have a communication function as an add-on. is there.

  However, based on the same idea as in Patent Document 2 for such a request, a circuit such as an electropneumatic conversion module provided in the conventional positioner from the beginning, a variable impedance circuit newly added for a communication function, and the like If the devices are designed to be connected in parallel, a large current consumption is added, which greatly affects the design and the basic circuit portion of the conventional positioner cannot be used as it is.

  The present invention has been made to solve such a problem, and the object of the present invention is to provide a communication function later by using the basic circuit unit of the conventional positioner as it is. Is to provide a simple positioner.

  In order to achieve such an object, the present invention receives a direct current signal from a host system via a pair of wires and generates its own operating power supply from the direct current signal, while the direct current signal In a positioner provided with a basic circuit unit that controls the opening of the control valve according to the value of and a communication function circuit unit that receives an alternating current signal transmitted superimposed on a direct current signal, The basic circuit unit and the communication function circuit unit are connected in series between the electric wires, and the communication function circuit unit includes a constant voltage control means for controlling the voltage between its terminals constant during non-communication, and an AC current signal during reception. And impedance varying means for changing the impedance of itself to a level higher than the impedance of the direct current signal.

  In this invention, the basic circuit part and the communication function circuit part of the positioner are connected in series. For this reason, a current flows in series between the communication function circuit unit and the basic circuit unit, and there is no additional current consumption. As a result, the basic circuit portion of the conventional positioner can be used as it is, and a communication function can be provided later.

  In the present invention, the communication function circuit unit includes a constant voltage control unit and an impedance variable unit. As a first configuration example thereof, as the constant voltage control unit, for example, a current connected between terminals of the communication function circuit unit. The control element, the voltage dividing circuit connected between the terminals of the communication function circuit unit, the divided voltage generated by the voltage dividing circuit and the reference voltage are compared, and the current flowing through the current control element is determined so that they match. It is conceivable to use a low voltage filter connected between the operational amplifier and the current control element as the impedance variable means using a constant voltage circuit including an operational amplifier to be controlled.

  In the first configuration example, when the communication function circuit unit has a transmission function for superimposing transmission information to the higher-order system supplied through the operational amplifier on the DC current signal, the transmission of information to the higher-order system is performed. When performing, the low pass filter may be disconnected from the connection path between the operational amplifier and the current control element.

  In the present invention, the communication function circuit unit includes a constant voltage control unit and an impedance variable unit. As a second configuration example, the constant voltage control unit includes, for example, a current connected between terminals of the communication function circuit unit. The control element, the voltage dividing circuit connected between the terminals of the communication function circuit unit, the divided voltage generated by the voltage dividing circuit and the reference voltage are compared, and the current flowing through the current control element is determined so that they match. It is conceivable to use a constant voltage circuit including an operational amplifier to be controlled, and to use a capacitor connected between the output terminal of the operational amplifier and the input terminal of the reference voltage as the impedance variable means.

  In the second configuration example, when the communication function circuit unit has a transmission function for superimposing transmission information to the higher-order system supplied through the operational amplifier on the DC current signal, transmission of information to the higher-order system is performed. When performing, the connection path through the capacitor between the output terminal of the operational amplifier and the input terminal of the reference voltage may be cut off.

  In the second configuration example, transmission information to the higher-level system may be given from a connection path between the operational amplifier and the current control element, instead of being given through the operational amplifier. This eliminates the need to block the connection path between the output terminal of the operational amplifier and the input terminal of the reference voltage during transmission, and simplifies the design due to the independence of the reception impedance and transmission signal. To be able to.

  According to the present invention, the basic circuit unit and the communication function circuit unit are connected in series, and the communication function circuit unit has constant voltage control means for controlling the voltage between its own terminals at the time of non-communication, and AC voltage at the time of reception. Since the impedance variable means for changing the self impedance for the current signal to a level higher than the impedance for the DC current signal is provided, a large current consumption is not added, and the basic circuit portion of the conventional positioner is provided. It is possible to use it as it is and to have a communication function later.

  Further, according to the present invention, the communication function circuit unit includes a constant voltage control means for controlling the voltage between its terminals to be constant during non-communication, and a self-impedance with respect to an alternating current signal during reception to an impedance with respect to a direct current signal. Compared with a system in which a variable impedance circuit is provided between the basic circuit section and the communication function circuit section, the voltage between the terminals of the positioner is reduced by adopting a configuration that includes an impedance variable means that changes the level to a higher level. It is also possible to obtain the effect that the

It is a figure which shows the structure of the principal part of one Embodiment of the positioner which concerns on this invention. It is a figure which shows the structure of the principal part of the conventional positioner. It is a figure which shows the 1st example of the communication function circuit in the positioner of this Embodiment. It is a figure which shows the 2nd example of the communication function circuit in the positioner of this Embodiment. It is a figure which shows the 3rd example of the communication function circuit in the positioner of this Embodiment. It is a block diagram (reference drawing) of the principal part of a positioner at the time of setting it as a system which provides a variable impedance circuit between a communication function circuit part and a basic circuit part.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the conventional positioner will be described first, and then the positioner of the present embodiment will be described.

[Conventional positioner]
FIG. 2 shows the configuration of the main part of the conventional positioner. In FIG. 2, reference numeral 100 denotes a conventional positioner, which is attached to the control valve 200.

  A DC current signal of 4 to 20 mA is input to the input terminals T1 and T2 of the conventional positioner 100 from the host system via the pair of electric wires L1 and L2. The Zener diode ZD1 is connected between the input terminals T1 and T2 via the resistor RA, and generates a power supply voltage V1 for an internal circuit such as the CPU1. The capacitor CB1 is a decoupling circuit for the power supply voltage V1, and prevents energy transfer and feedback between the power supply voltage V1 and the ground GND.

  The current detection circuit 2 detects the value of the DC current signal input to the input terminals T1 and T2, and the detected value of the DC current signal is sent to the A / D converter 3. The CPU 1 controls the opening degree of the control valve 200, and a control program such as PID control is stored in the memory M1. The D / A converter 4 converts the control output of the CPU 1 from a digital signal into an analog signal.

  The drive circuit 5 amplifies or impedance-converts the analog signal sent from the D / A converter 4 to generate a current signal Io and supplies it to the electropneumatic conversion module 7. The sensor interface circuit 6 processes the valve opening signal from the position sensor 9 and sends it to the A / D converter 3. The A / D converter 3 converts the value of the DC current signal sent from the current detection circuit 2 and the value of the valve opening signal sent from the sensor interface circuit 6 into a digital signal and sends it to the CPU 1.

  The electropneumatic conversion module 7 converts the input current signal Io into an air pressure signal Pn, and controls the air pressure of the nozzle. The control relay 8 amplifies the air pressure signal Pn, and opens and closes the control valve 200 by the amplified air pressure signal Pout.

  The opening degree control of the control valve 200 is performed by sending the valve opening degree signal of the position sensor 9 to the CPU 1 via the sensor interface circuit 6 and the A / D converter 3, and the CPU 1 performs control calculation and D / A converts the control output. This is done by sending it to the drive circuit 5 via the device 4. As a result, the control valve 200 is driven through the path of the drive circuit 5 → the electropneumatic conversion module 7 → the control relay 8 → the control valve 200 to control the valve opening to the target value.

  In this conventional positioner 100, a Zener diode ZD1, a resistor RA, a capacitor CB1, CPU1, a current detection circuit 2, an A / D converter 3, a D / A converter 4, and a drive circuit connected between input terminals T1 and T2. 5, all circuit configurations including the sensor interface circuit 6 are defined as a basic circuit unit 10.

[Positioner of this embodiment]
FIG. 1 shows a configuration of a main part of the positioner according to the present embodiment. 2, the same reference numerals as those in FIG. 2 denote the same or equivalent components as those described with reference to FIG. 2, and the description thereof will be omitted. In order to distinguish from the conventional positioner 100 shown in FIG.

  In the positioner 101 of the present embodiment, the basic circuit section 10 of the conventional positioner 100 and the communication function circuit section 11 unique to the present embodiment are connected in series between the input terminals T1 and T2.

  In this positioner 101, the communication function circuit unit 11 includes a communication function circuit 12, a modem 13, and a capacitor CB2. The communication function circuit 12 has a reception function and a transmission function. The communication function circuit 12 receives information transmitted from the upper system by the reception function by digital communication, and transmits information to the upper system by the transmission function by digital communication.

  The contents of communication using the communication function circuit 12 include control parameters for control calculation with respect to the control valve 200, the adjustment amount of the zero / span point, the actual opening of the control valve 200, and transmission / reception of self-diagnosis results. . In this communication, information is received through the path of communication function circuit 12 → modem 13 → CPU1, and information is transmitted through the path of CPU1 → modem 13 → communication function circuit 12.

[First example of communication function circuit]
FIG. 3 shows a first example of the communication function circuit 12. The communication function circuit 12 (12A) of the first example includes a constant voltage control circuit 121, a low-pass filter 122, a switch SW1, and resistors RB and RC, and is connected to terminals P1 and P2 of the communication function circuit unit 11. Connected between connection lines LA and LB.

  The constant voltage control circuit 121 includes a transistor Q1, a diode D1, an operational amplifier OP1, resistors R1 to R8, capacitors C3 and C4, and a Zener diode ZD2. The collector of the transistor Q1 is connected to the terminal P1. Connected to the connection line LA, the emitter of the transistor Q1 is connected to the connection line LB to the terminal P2 via the diode D1 and the resistor RB. This transistor Q1 corresponds to a current control element in the present invention.

  In the constant voltage control circuit 121, a series circuit of resistors R1 and R2 is connected as a voltage dividing circuit between the lines LA and LB, and a voltage generated at a connection point between the resistors R1 and R2 is a voltage dividing circuit. Is supplied to the non-inverting input terminal of the operational amplifier OP1 as the divided voltage Vpv generated by

  In addition, a parallel circuit of a capacitor C3 and a Zener diode ZD2 is connected between the lines LA and LB via a resistor R5. The parallel circuit of the capacitor C3 and the Zener diode ZD2 is connected to the resistor R5. The voltage is applied to the inverting input terminal of the operational amplifier OP1 as the reference voltage Vs through the resistor R3.

  The output terminal of the operational amplifier OP1 is connected to the base of the transistor Q1 via a low-pass filter 122 and a resistor R7, and a switch SW1 is provided on a connection line between the low-pass filter 122 and the resistor R7. This low-pass filter 122 corresponds to the impedance variable means in the present invention.

  The switch SW1 is a one-circuit / two-contact switch, the first contact a is connected to the output side of the low-pass filter 122, and the second contact b is connected to the input side of the low-pass filter 122. The operation of the switch SW1 is controlled by a command from the CPU 1, and the connection mode to the first contact a is normally set (during non-communication and reception), and the connection mode to the second contact b only at the time of transmission. It is said.

[Non-communication]
During non-communication, the operational amplifier OP1 of the communication function circuit 12A compares the divided voltage Vpv with the reference voltage Vs and outputs a comparison output that matches the two. This comparison output passes through the low-pass filter 122, passes through the switch SW1 in the connection mode to the first contact a, and is given to the base of the transistor Q1 through the resistor R7. Thereby, the current flowing through the transistor Q1 is adjusted so that the divided voltage Vpv and the reference voltage Vs match, that is, the voltage between the terminals P1 and P2 of the communication function circuit unit 11 is constant (for example, 5 V). Be controlled.

[When receiving]
During reception, the operational amplifier OP1 of the communication function circuit 12A compares the divided voltage Vpv with the reference voltage Vs and outputs a comparison output that matches the two. This comparison output passes through the low-pass filter 122, passes through the switch SW1 in the connection mode to the first contact a, and is given to the base of the transistor Q1 through the resistor R7.

  Here, at the time of reception, an alternating current signal is superimposed on a direct current signal from the host system. In this case, since the low-pass filter 122 is inserted between the operational amplifier OP1 and the resistor R7, the AC component does not easily pass through the low-pass filter 122, and the loop gain of the shunt regulator in the signal frequency band (950 Hz to 2500 Hz). Becomes smaller and feedback becomes difficult.

  As a result, at the time of reception, the control operation of the current flowing through the transistor Q1 becomes dull, and the impedance to the AC current signal changes to a level higher than the impedance to the DC current signal, and the connection point between the resistor RB and the diode D1 The received signal is taken out and sent to the modem 13 as a change in voltage (for example, a change width of 500 mV).

[When sending]
At the time of transmission, the CPU 1 sets the switch SW1 to the connection mode to the second contact b, and sends transmission information to the higher-level system to the modem 13. As a result, the low-pass filter 122 is disconnected from the connection path between the operational amplifier OP1 and the transistor Q1, and in this state, transmission information from the modem 13 is applied to the inverting input terminal of the operational amplifier OP1 via the resistor RC. .

  The transmission information given to the inverting input terminal of the operational amplifier OP1 passes through the bypass LC that bypasses the low-pass filter 122, passes through the switch SW1 that is in the connection mode to the second contact b, and passes through the resistor R7. Applied to the base of transistor Q1. As a result, the transmission information is superimposed on the current flowing through the transistor Q1, and is sent to the host system.

[Second example of communication function circuit]
FIG. 4 shows a second example of the communication function circuit 12. Similarly to the communication function circuit 12A of the first example, the communication function circuit 12 (12B) of the second example is also connected between the connection lines LA and LB with the terminals P1 and P2 of the communication function circuit unit 11.

  The communication function circuit 12B of the second example is different from the communication function circuit 12A of the first example in that a capacitor C5 is provided instead of the low-pass filter 122, and this capacitor C5 is connected between the output terminal and the inverting input terminal of the operational amplifier OP1. It is in the place where it is connected to. Further, a switch SW2 having one circuit and one contact is provided instead of the switch SW1, and this switch SW2 is provided in a connection path LD between the output terminal and the inverting input terminal of the operational amplifier OP1 via the capacitor C5.

  In the communication function circuit 12B, the operation of the switch SW2 is controlled by a command from the CPU 1, and is normally turned on (during non-communication and reception) and is turned off only during transmission. Further, in this communication function circuit 12B, the capacitor C5 connected between the output terminal and the inverting input terminal of the operational amplifier OP1 corresponds to the impedance variable means referred to in the present invention. The rest is the same as the communication function circuit 12A of the first example, and the description thereof is omitted.

[Non-communication]
During non-communication, the operational amplifier OP1 of the communication function circuit 12B compares the divided voltage Vpv with the reference voltage Vs and outputs a comparison output that matches the two. This comparison output is given to the base of the transistor Q1 through the resistor R7. Thereby, the current flowing through the transistor Q1 is adjusted so that the divided voltage Vpv and the reference voltage Vs match, that is, the voltage between the terminals P1 and P2 of the communication function circuit unit 11 is constant (for example, 5 V). Be controlled.

[When receiving]
At the time of reception, the operational amplifier OP1 of the communication function circuit 12B compares the divided voltage Vpv with the reference voltage Vs and outputs a comparison output that matches the two. This comparison output is given to the base of the transistor Q1 through the resistor R7.

  Here, at the time of reception, an alternating current signal is superimposed on a direct current signal from the host system. In this case, since the capacitor C5 is inserted in the connection path LD between the output terminal of the operational amplifier OP1 and the inverting input terminal, an AC component passes through the capacitor C5, and the shunt regulator in the signal frequency band (950 Hz to 2500 Hz). The loop gain becomes smaller, making it difficult to apply feedback.

  As a result, at the time of reception, the control operation of the current flowing through the transistor Q1 becomes dull, and the impedance to the AC current signal changes to a level higher than the impedance to the DC current signal, and the connection point between the resistor RB and the diode D1 The received signal is taken out and sent to the modem 13 as a change in voltage (for example, a change width of 500 mV).

[When sending]
At the time of transmission, the CPU 1 turns off the switch SW2 and sends transmission information to the higher system to the modem 13. As a result, the connection path LD between the output terminal of the operational amplifier OP1 and the inverting input terminal via the capacitor C5 is cut off, and in this state, transmission information from the modem 13 is given to the inverting input terminal of the operational amplifier OP1 through the resistor RC. It will be.

  The transmission information given to the inverting input terminal of the operational amplifier OP1 is given to the base of the transistor Q1 via the resistor R7 without being returned to the inverting input terminal of the operational amplifier OP1 by the capacitor C5. As a result, the transmission information is superimposed on the current flowing through the transistor Q1, and is sent to the host system.

  In this communication function circuit 12B, the low-pass filter 122 in the communication function circuit 12A is replaced with one capacitor C5, and the switch SW2 may be a simple switch. As a result, the circuit configuration can be simplified and the cost can be reduced.

[Third example of communication function circuit]
FIG. 5 shows a third example of the communication function circuit 12. Similarly to the communication function circuit 12A of the first example and the communication function circuit 12B of the second example, the communication function circuit 12 (12C) of the third example also has a connection line LA to the terminals P1 and P2 of the communication function circuit unit 11. , LB.

  This communication function circuit 12C of the third example is different from the communication function circuit 12B of the second example in that the switch SW2 is eliminated and a capacitor C5 is fixedly connected between the output terminal and the inverting input terminal of the operational amplifier OP1. The transmission circuit 123 is provided so as to provide transmission information to the higher-order system from the connection path between the operational amplifier OP1 and the transistor Q1. Others are the same as those of the communication function circuit 12B of the second example, and thus the description thereof is omitted.

  In this communication function circuit 12C, the transmission circuit 123 is composed of an operational amplifier OP2, resistors R9 to R14, and capacitors C6 to C8, and a non-inverting input terminal of the operational amplifier OP2 along the path of the capacitors C6 and R11. Is sent to the host system, and is sent from the output terminal of the operational amplifier OP2 to the base of the transistor Q1 through the path of the capacitor C7 and the resistor R14.

[Non-communication]
During non-communication, the operational amplifier OP1 of the communication function circuit 12C compares the divided voltage Vpv with the reference voltage Vs and outputs a comparison output that matches the two. This comparison output is given to the base of the transistor Q1 through the resistor R7. Thereby, the current flowing through the transistor Q1 is adjusted so that the divided voltage Vpv and the reference voltage Vs match, that is, the voltage between the terminals P1 and P2 of the communication function circuit unit 11 is constant (for example, 5 V). Be controlled.

[When receiving]
At the time of reception, the operational amplifier OP1 of the communication function circuit 12C compares the divided voltage Vpv with the reference voltage Vs and outputs a comparison output that matches the two. This comparison output is given to the base of the transistor Q1 through the resistor R7.

  Here, at the time of reception, an alternating current signal is superimposed on a direct current signal from the host system. In this case, since the capacitor C5 is inserted in the connection path LD between the inverting input terminal and the output terminal of the operational amplifier OP1, the AC component passes through the capacitor C5, and the shunt in the signal frequency band (950 Hz to 2500 Hz). The loop gain of the regulator is reduced, making it difficult to apply feedback.

  As a result, at the time of reception, the control operation of the current flowing through the transistor Q1 becomes dull, and the impedance to the AC current signal changes to a level higher than the impedance to the DC current signal, and the connection point between the resistor RB and the diode D1 The received signal is taken out and sent to the modem 13 as a change in voltage (for example, a change width of 500 mV).

[When sending]
At the time of transmission, the CPU 1 sends transmission information to the host system to the modem 13. This transmission information is sent to the transmission circuit 123. In the transmission circuit 123, transmission information to the host system is given to the non-inverting input terminal of the operational amplifier OP2 through the path of the capacitor C6 and the resistor R11, and from the output terminal of the operational amplifier OP2 to the transistor Q1 through the path of the capacitor C7 and the resistor R14. Sent to the base. As a result, the transmission information is superimposed on the current flowing through the transistor Q1, and is sent to the host system.

  In this communication function circuit 12C, it is not necessary to cut off the connection path LD via the capacitor 5 between the inverting input terminal and the output terminal of the operational amplifier OP1 at the time of transmission, and the design is easy due to the independence of the reception impedance and the transmission signal. It becomes possible to.

  As can be seen from the above description, according to the positioner 101 of the present embodiment, the basic circuit unit 10 and the communication function circuit unit 11 of the conventional positioner 100 are connected in series. The basic circuit unit 10 can be provided with a communication function by using the basic circuit unit 10 of the conventional positioner 100 as it is without adding a large current consumption. Become. This means that when two types of positioners with a communication function and positioners without a communication function are prepared, the basic circuit unit can use both models in common.

  Further, according to the positioner 101 of the present embodiment, the communication function circuit 12 is configured such that the constant voltage control circuit 121 that controls the voltage between its terminals to be constant during non-communication, and the self-impedance with respect to the AC current signal during reception. Since impedance varying means (low-pass filter 122 in the first example communication function circuit 12A and capacitor C5 in the second example communication function circuit 12B) is provided to change the level higher than the impedance to the DC current signal, the communication function Compared with a method in which a variable impedance circuit is provided between the circuit unit and the basic circuit unit, the voltage between terminals of the positioner can be reduced.

  FIG. 6 is a configuration diagram (reference diagram) of a main part of the positioner when a variable impedance circuit is provided between the communication function circuit unit and the basic circuit unit. Also in this positioner 102, the communication function circuit unit 15 is connected in series to the basic circuit unit 10 of the conventional positioner 100. However, the communication function circuit 14 in the communication function circuit unit 15 is configured by a simple reception circuit, transmission circuit, or the like, and the variable impedance circuit 16 is connected in series between the basic circuit unit 10 and the communication function circuit unit 15. .

  In this positioner 102, since the variable impedance circuit 16 is connected in series between the basic circuit unit 10 and the communication function circuit unit 15, the voltage between the terminals of the positioner 102 increases by the voltage drop in the variable impedance circuit 16. However, there is a problem that the voltage between the terminals of the positioner 102 becomes too large.

  On the other hand, in the positioner 101 according to the present embodiment, the communication function circuit unit 11 is provided with the communication function circuit 12 having both the operation power supply function and the variable impedance function, so that the basic circuit unit 10, the communication function circuit unit 11, The need to provide a variable impedance circuit between them is eliminated. For this reason, in the positioner 101 of the present embodiment, there is no variable impedance circuit between the basic circuit unit 10 and the communication function circuit unit 11, and the voltage across the terminals of the positioner 101 is reduced by the amount of this variable impedance circuit. Is able to.

  In the above-described embodiment, the positioner 101 has a transmission / reception function as a communication function. However, the positioner 101 does not necessarily have a transmission function, and may have only a reception function.

  In the embodiment described above, the low-pass filter 122 and the capacitor C5 are used as the impedance variable means in the communication function circuit 12. However, the self-impedance with respect to the AC current signal at the time of reception is higher than the impedance with respect to the DC current signal. Any function can be used as long as it can realize a function that can be changed to a high level, and the present invention is not limited to the low-pass filter 122 or the capacitor C5.

[Extension of the embodiment]
The present invention has been described above with reference to the embodiment, but the present invention is not limited to the above embodiment. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention. In addition, each example of the communication function circuit 12 described above can be implemented in any combination within a consistent range.

  The positioner of the present invention can be used in various fields such as process control as a device for controlling the opening of the control valve.

  DESCRIPTION OF SYMBOLS 1 ... CPU, 2 ... Current detection circuit, 3 ... A / D converter, 4 ... D / A converter, 5 ... Drive circuit, 6 ... Sensor interface circuit, 7 ... Electropneumatic conversion module, 8 ... Control relay, 9 ... Position sensor, 10 ... Basic circuit part, 11 ... Communication function circuit part, 12 (12A, 12B, 12C) ... Communication function circuit, 13 ... Modem, 121 ... Constant voltage control circuit, 122 ... Low pass filter, SW1 ... Switch, Q1 ... transistor, OP1 ... op amp, C5 ... capacitor, SW2 ... switch, 123 ... transmission circuit, 101 ... positioner, 200 ... regulator valve.

Claims (6)

Receives a DC current signal from the host system via a pair of wires, generates its own operating power supply from this DC current signal, and controls the opening of the control valve according to the value of the DC current signal In a positioner comprising a basic circuit part and a communication function circuit part for receiving an alternating current signal transmitted superimposed on the direct current signal,
The basic circuit unit and the communication function circuit unit are connected in series between the pair of electric wires,
The communication function circuit unit is
Constant voltage control means for controlling the voltage between its own terminals at the time of non-communication,
A positioner comprising: impedance changing means for changing its own impedance with respect to the AC current signal to a level higher than the impedance with respect to the DC current signal during reception. The positioner as claimed in claim 1,
The constant voltage control means includes
The current control element connected between the terminals of the communication function circuit unit, the voltage dividing circuit connected between the terminals of the communication function circuit unit, and the divided voltage generated by the voltage dividing circuit and the reference voltage are compared. And a constant voltage circuit including an operational amplifier that controls a current flowing through the current control element so that the two match.
The impedance varying means is
A positioner comprising a low-pass filter connected between the operational amplifier and the current control element. The positioner according to claim 2, wherein
The communication function circuit unit is
A transmission function for superimposing transmission information to the higher-order system given through the operational amplifier on the DC current signal,
The positioner wherein the low-pass filter is disconnected from a connection path between the operational amplifier and the current control element when transmitting information to the host system. The positioner as claimed in claim 1,
The constant voltage control means includes
The current control element connected between the terminals of the communication function circuit unit, the voltage dividing circuit connected between the terminals of the communication function circuit unit, and the divided voltage generated by the voltage dividing circuit and the reference voltage are compared. And a constant voltage circuit including an operational amplifier that controls a current flowing through the current control element so that the two match.
The impedance varying means is
A positioner comprising a capacitor connected between an output terminal of the operational amplifier and an input terminal of a reference voltage. The positioner according to claim 4, wherein
The communication function circuit unit is
A transmission function for superimposing transmission information to the higher-order system given through the operational amplifier on the DC current signal,
When transmitting information to the higher-order system, the connection path via the capacitor between the output terminal of the operational amplifier and the input terminal of the reference voltage is cut off. The positioner according to claim 4, wherein
The communication function circuit unit is
A positioner comprising: a transmission circuit that provides transmission information to the higher-order system to be superimposed on the DC current signal from a connection path between the operational amplifier and the current control element.

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