JP5706213B2 - 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 having a function of transmitting to has been proposed. FIG. 3 shows a configuration of a main part of a positioner having a communication function with a host system (see, for example, Patent Document 2).

  In FIG. 3, a DC current signal of 4 to 20 mA is input to the input terminals T1 and T2. The Zener diode D1 is connected to the input terminals T1 and T2 via the resistor RA, and generates a power supply voltage V1 for internal circuits such as the modem 4 and the CPU 6. The capacitor CA is inserted between the transmission circuit 1 and the reception circuit 2 and the input terminal T2, and insulates the power supply voltage V1 and the digital communication signal in a DC manner. The capacitor CB 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 transmission circuit 1 transmits a response signal to the higher system by digital communication. The receiving circuit 2 receives a request signal sent from the higher system. Here, the host system is connected to the input terminals T1 and T2 via a two-wire transmission line (a pair of electric wires). In addition, in the digital communication of the transmission / reception circuits 1 and 2, the impedance by the resistor RA is effectively used so that a communication amplitude of a certain voltage level or more can be secured. The current detection circuit 3 detects a current signal input to the input terminals T <b> 1 and T <b> 2, and the detected signal is sent to the A / D converter 7.

  The modem 4 performs modulation / demodulation of digital communication of the transmission / reception circuits 1 and 2, and exchanges transmission / reception contents with the CPU 6. The CPU 6 performs digital communication and position control of the control valve 14, and a communication processing program such as a request signal and a response signal and a control program such as PID control are stored in the memory 5. The D / A converter 8 converts the control output of the CPU 6 from a digital signal into an analog signal.

  The drive circuit 9 amplifies and impedance converts the analog signal sent from the D / A converter 8 and sends it to the electropneumatic conversion module 11. The sensor interface circuit 10 processes the signal of the position sensor 13 and sends it to the A / D converter 7. The A / D converter 7 converts the input current signal sent from the current detection circuit 3 and the control valve position signal sent from the sensor interface circuit 10 into a digital signal and sends it to the CPU 6.

  The electropneumatic conversion module 11 converts the input drive current into an air pressure signal, and controls the air pressure of the nozzle by a torque motor. The control relay 12 amplifies the air pressure signal, and opens and closes the control valve 14 by the amplified air pressure signal. In order to control the opening degree of the control valve 14, the position signal of the position sensor 13 is sent to the CPU 6 via the sensor interface circuit 10 and the A / D converter 7, and the CPU 6 performs a control operation and outputs the control output to the D / A converter 8. Is sent to the drive circuit 9 via. As a result, the control valve 14 is driven and the valve opening degree is controlled to the target value through the path of the drive circuit 9 → the electropneumatic conversion module 11 → the control relay 12 → the control valve 14.

  In this positioner 100, communication is possible between the host system and the positioner 100 by superimposing an alternating current signal on a direct current signal of 4 to 20 mA. The contents of the communication are control parameters for the control calculation for the control valve 14, zero / span point adjustment amount, displacement sensor signal output, and transmission / reception of self-diagnosis results. The communication data is read in the path of the receiving circuit 2 → the modem 4 → the CPU 6 and the communication data is transmitted in the path of the CPU 6 → the modem 4 → the transmitting circuit 1. The DC current signal input to the positioner 100 is recognized through the path of the current detection circuit 3 → A / D converter 7 → CPU 6.

  In this positioner 100, in order to perform digital communication, it is necessary that the resistance RA is approximately 250Ω or more. When the input current is 20 mA, the voltage drop is 5 V or more, and the voltage V1 generated by the Zener diode D1 is reduced. Therefore, instead of the resistor RA, a variable impedance circuit Z1 as shown in FIG. 4 is used as an active load.

  In the variable impedance circuit Z1, the transistor Q1 has a collector connected to the line L1 and an emitter connected to the line L2 via the resistor R11. The transistor Q2 has a collector connected to the line L1 and a base via a resistor R13, and an emitter connected to the base of the transistor Q1 and also connected to a line L2 via a resistor R12. The base of the transistor Q2 is connected to the line L2 via a parallel circuit of a resistor R14, a capacitor C11, and a resistor R15. The line L1 is a connection line to the Zener diode D1, and the line L2 is a connection line to the terminal T2.

  FIG. 5 is an impedance characteristic diagram of the variable impedance circuit Z1. As can be seen from this impedance characteristic diagram, the variable impedance circuit Z1 has a characteristic that the impedance (| Z |) is low in the low frequency region and the impedance (| Z |) is high in the high frequency region. That is, the impedance with respect to the direct current signal is low, and the impedance with respect to the alternating current signal is higher than the impedance with respect to the direct current signal. By using such a variable impedance circuit Z1, the voltage drop in the variable impedance circuit Z1 can be reduced, and the voltage V1 generated by the Zener diode D1 can be increased.

JP 2004-151941 A Japanese Patent Laid-Open No. 11-304033 (Patent No. 3596293)

Recently, there has been a demand for a positioner having such a communication function such that two positioners are connected in series (two linked) between two transmission lines. However, even with a positioner using the above-described variable impedance circuit Z1, it has been difficult to realize such a usage method.

  For example, when the supply voltage from the two-wire transmission line is 15V, when two positioners are connected, the voltage between terminals of the positioner is 7.5V. In this case, if at least 5V is required as the power supply voltage of the internal circuit, the voltage drop in the variable impedance circuit Z1 is allowed only to 2.5V.

  However, the conventional variable impedance circuit Z1 shown in FIG. 4 has a configuration in which the transistors Q1 and Q2 are Darlington-connected, so that the impedance (DC impedance) for a DC current signal is large, and the variable impedance circuit The voltage drop at Z1 cannot be 2.5 V or less. For this reason, the terminal-to-terminal voltage at which the positioner can operate (minimum operating terminal voltage) cannot be 7.5 V or less, and two positioners cannot be connected between two transmission lines.

The present invention has been made to solve such a problem. The object of the present invention is to realize a two-connection between two transmission lines by reducing the minimum operating terminal voltage. To provide a possible 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 the positioner that controls the opening of the control valve according to the value of the DC and receives the AC current signal that is sent superimposed on the DC current signal, the impedance to the DC current signal is low, and the AC current signal A variable impedance circuit having characteristics higher than that of a DC current signal. The variable impedance circuit includes a DC current signal, an input line of an AC current signal superimposed on the DC current signal, and a DC current signal. The output line of the alternating current signal superimposed on the current signal and the direct current signal, and the input line and the output line A series circuit of a first resistor and a second resistor connected to each other, a transistor having a collector connected to the input line and a base connected to a connection point between the first resistor and the second resistor, A third resistor connected between the emitter of the transistor and the output line, a capacitor having one end connected to a connection point between the first resistor and the second resistor, and the other end of the capacitor and the output line And a fourth resistor connected to each other, and the presence of the variable impedance circuit allows two positioners to be connected in series between a pair of wires (two connected). And

  According to the present invention, the variable impedance circuit is provided with a single transistor, and the voltage generated at the connection point between the first resistor and the second resistor at the base of the single transistor, that is, the capacitor and the fourth resistor. A voltage applied to the parallel circuit of the series circuit and the second resistor is applied. As a result, the characteristic of the variable impedance circuit is that the impedance to the direct current signal is low and the impedance to the alternating current signal is high. In this case, since the variable impedance circuit operates with only one transistor, the DC impedance is reduced, and the voltage drop in the variable impedance circuit can be further reduced.

According to the positioner of the present invention, since the variable impedance circuit is operated by a single transistor, the DC impedance is reduced, the voltage drop in the variable impedance circuit can be further reduced, and the minimum operating terminal voltage is reduced. As a result, it is possible to realize two connections between two transmission lines.

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 variable impedance circuit used for this positioner. It is a figure which shows the structure of the principal part of the conventional positioner which has a communication function between high-order systems. It is a figure which shows the structure of the variable impedance circuit used as an active load in the conventional positioner. It is an impedance characteristic view of this variable impedance circuit.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a configuration of a main part of an embodiment of a positioner according to the present invention. 3, the same reference numerals as those in FIG. 3 denote the same or equivalent components as those described with reference to FIG. 3, and the description thereof will be omitted.

  In the positioner 200 of the present embodiment, a variable impedance circuit Z2 as shown in FIG. 2 is used as an active load. That is, the line L1 is an input line for a direct current signal and an alternating current signal superimposed on the direct current signal, and the line L2 is an output line for an alternating current signal superimposed on the direct current signal and the direct current signal. A variable impedance circuit Z2 is connected between the input line L1 and the output line L2.

  The variable impedance circuit Z2 includes a series circuit of a first resistor R1 and a second resistor R2 connected between the input line L1 and the output line L2, and a collector connected to the input line L1. Is connected to a connection point between the first resistor R1 and the second resistor R2, a third resistor R3 connected between the emitter of the transistor Q1 and the output line L2, and a first resistor The capacitor C1 has one end connected to a connection point between the R1 and the second resistor R2, and a fourth resistor R4 connected between the other end of the capacitor C1 and the output line L2.

  In this variable impedance circuit Z2, the voltage generated at the connection point between the first resistor R1 and the second resistor R2 at the base of the transistor Q1, that is, the series circuit of the capacitor C1 and the fourth resistor R4, and the second resistor R2 Voltage applied to the parallel circuit. Thereby, as the characteristics of the variable impedance circuit Z2, it is possible to obtain the characteristics that the impedance to the direct current signal is low and the impedance to the alternating current signal is high.

  In this case, the conventional variable impedance circuit Z1 (FIG. 4) is operated by transistors Q1 and Q2 connected in Darlington, but the variable impedance circuit Z2 of the present embodiment is operated by only one transistor Q1. Impedance is reduced, and the voltage drop in the variable impedance circuit Z2 is further reduced.

  For example, in the present embodiment, the voltage drop in the variable impedance circuit Z2 is 1.3V. Therefore, when the power supply voltage of the internal circuit in the positioner 200 is 5V, that is, when the voltage V1 generated by the Zener diode D1 is 5V, the minimum operating terminal voltage of the positioner 200 is 6.3V.

  Thereby, for example, when the supply voltage from the two-wire transmission line is 15V, when the positioner 200 is connected in two, the voltage between the terminals of the positioner 200 becomes 7.5V. The positioner 200 can be operated. The same applies to the case where another load is connected to the positioner 200, and it is possible to cope until the voltage between the terminals becomes 6.3 V or less.

  Further, in the variable impedance circuit Z2 of the present embodiment, the transistor Q2 and the resistor R12 are omitted, as can be seen in comparison with the conventional variable impedance circuit Z1 shown in FIG. This simplifies, reduces the number of parts, and reduces costs.

  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 ... Transmission circuit, 2 ... Reception circuit, 3 ... Current detection circuit, 4 ... Modem, 5 ... Memory, 6 ... CPU, 7 ... A / D converter, 8 ... D / A converter, 9 ... Drive circuit, 10 DESCRIPTION OF SYMBOLS ... Sensor interface circuit, 11 ... Electropneumatic conversion module, 12 ... Control relay, 13 ... Position sensor, 14 ... Control valve, T1, T2 ... Input terminal, D1 ... Zener diode, CA, CB ... Capacitor, Z2 ... Variable impedance circuit , L1 ... input line, L2 ... output line, Q1 ... transistor, R1 ... first resistor, R2 ... second resistor, R3 ... third resistor, R4 ... fourth resistor, C1 ... capacitor, 200 ... positioner .

Claims (1)

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 addition, in a positioner that receives an alternating current signal sent superimposed on the direct current signal,
A variable impedance circuit having a low impedance with respect to the DC current signal and having a characteristic that an impedance with respect to the AC current signal is higher than an impedance with respect to the DC current signal;
The variable impedance circuit is:
An input line of the DC current signal and an AC current signal superimposed on the DC current signal;
An output line of the DC current signal and an AC current signal superimposed on the DC current signal;
A series circuit of a first resistor and a second resistor connected between the input line and the output line;
A transistor having a collector connected to the input line and a base connected to a connection point between the first resistor and the second resistor;
A third resistor connected between the emitter of the transistor and the output line;
A capacitor having one end connected to a connection point between the first resistor and the second resistor;
A fourth resistor connected between the other end of the capacitor and the output line ;
The positioner is
A positioner wherein two variable impedance circuits can be connected in series between the pair of electric wires due to the presence of the variable impedance circuit .

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