JP2012207755A - Positioner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive voltage-input type positioner that establishes communication by simply modifying a conventional current-input type positioner.SOLUTION: A voltage-current converting circuit 1-5 is provided in a stage prior to a communication circuit 1-2. The voltage-current converting circuit 1-5 has impedance characteristics where the impedance Z becomes extremely low for a communication signal (alternating current electric signal) and the impedance Zsig becomes high for a DC signal (direct-current electric signal). An AC voltage signal Vf from a communication device 3B is converted into an electric current by the impedance Z (Zf>>Z) in the voltage-current converting circuit 1-5, and transmitted to the current-input type communication circuit 1-2.

Description

  The present invention receives a DC electric signal from a host system via a pair of electric wires, generates its own operating power supply from the DC electric signal, and opens the control valve according to the value of the DC electric 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, if the control valve is a proportional valve and the current of 4 mA is sent from the host system, the opening of the proportional valve is 0%, and if the current of 20 mA is sent, the opening of the proportional 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. 6 shows a configuration of a main part of a system using a positioner having a communication function with the host system.

  In FIG. 6, 1 is a positioner, 2 is a host device connected to the positioner 1 via two-wire transmission lines (a pair of electric wires) L1 and L2, and 3 is connected between the transmission lines L1 and L2 as necessary. 4 is an upper system, 5 is a control valve (proportional valve). The positioner 1 includes a main circuit 1-1, a communication circuit 1-2, and a constant voltage circuit 1-3. In the case of this example, the host system 4 is composed of a host device 2 and a communication device 3.

  In this system, the host device 2 sends a DC current signal I of 4 to 20 mA to the positioner 1 via the transmission lines L1 and L2. In the positioner 1, the constant voltage circuit 1-3 generates a constant voltage Vpos from the DC current signal I sent from the host device 2, and supplies the constant voltage Vpos to the communication circuit 1-2 and the main body circuit 1-1. The main circuit 1-1 controls the opening degree of the proportional valve 5 according to the value of the direct current signal I sent from the host device 2. Also, abnormality diagnosis of the proportional valve 5 and self abnormality diagnosis are performed.

  The communication device 3 superimposes a communication AC current signal If on a DC current signal I to the positioner 1. In the positioner 1, the communication circuit 1-2 is a current input type communication circuit, extracts an alternating current signal If superimposed on the direct current signal I, and is notified by the alternating current signal If. Commands and data from the device 3 are transmitted to the main circuit 1-1. Further, the communication circuit 1-2 changes the line voltage of the transmission lines L1 and L2, thereby transmitting the abnormality diagnosis result of the proportional valve 5 and the own abnormality diagnosis result from the main body circuit 1-1 to the communication device 3. . Such a communication method is disclosed in Patent Document 2.

  By the way, recently, there is a demand to perform abnormality diagnosis not only with a proportional valve but also with an on / off valve, and a positioner is sometimes applied. However, since the on / off valve may be controlled by two positions of full open and full close, usually a solenoid valve is generally used, and a pair of electric wires are used to operate the solenoid valve. A voltage signal (usually 0 to 24 V) is input. Therefore, the internal circuit of the positioner that controls the valve opening degree of such an on / off valve needs to be adapted to voltage input.

  For example, in Patent Document 2, if one communication device is a positioner and the other communication device is a host device, the host device superimposes a communication AC voltage signal on a DC voltage signal that fluctuates within a predetermined range. The positioner side extracts a DC voltage signal from the voltage signal received from the host device, controls the opening of the control valve based on the value of the DC voltage signal, and controls the host device. By changing the line current that is fed back, the valve opening degree and the abnormality diagnosis result can be transmitted to the host device side. In this case, the positioner is compatible with voltage input and can be applied to an on / off valve. It is also possible to control the opening of the proportional valve by using the power supply of the host system as a voltage output type (DO: digital output) instead of a current output type (AO: analog output).

In addition, the system which supplies a voltage output type power supply is called a fieldbus system (for example, refer patent document 3), for example, supplies a voltage of 9-32V from a high-order system.
In the following, a type of positioner that inputs a DC current signal is referred to as a current input type positioner, and a type of positioner that inputs a DC voltage signal is referred to as a voltage input type positioner.

  In this case, a manufacturer that manufactures and supplies a positioner secures a communication function with the host system, and is compatible with an on / off valve or a fieldbus system. Two types of voltage input type positioners must be prepared, which is a manufacturing burden. In addition, the voltage input type positioner must be prepared as a different one from a general current input type positioner, and therefore it is expensive.

  Therefore, in order to eliminate this burden, Patent Document 4 discloses a dual-purpose positioner that can handle both current input from an analog transmission line and voltage input from a fieldbus transmission line with one model. Yes. This dual-purpose positioner is provided with an interface circuit (I / V block) connected to an analog transmission line and an interface circuit (FB block) connected to a fieldbus transmission line, and the I / V block and FB block are connected to each other. Switch to use as needed.

Japanese Patent Laid-Open No. 1-114102 Japanese Patent Laid-Open No. 61-070827 JP 2004-226092 A (Patent No. 4185369) JP 2002-367069 A

  However, in the dual-purpose positioner disclosed in Patent Document 4, the I / V block and the FB block must be provided separately, and the configuration becomes complicated, and the current input type positioner or voltage input type There is a problem that it becomes more expensive than other positioners.

  Therefore, the present applicant considered providing the fixed resistor 1-4 (see FIG. 7) in the previous stage of the communication circuit 1-2 in the current input type positioner 1 (1A) shown in FIG. In the system using the positioner 1 (1B), the higher-level device 2 (2B) sends a DC voltage signal V to the positioner 1B. Further, the communication device 3 (3B) superimposes the communication AC voltage signal Vf on the DC voltage signal V to the positioner 1B. The control valve 5 (5B) is a solenoid valve (on / off valve).

  In this positioner 1B, the DC voltage signal V from the host device 2B is converted into a current by the fixed resistor 1-4 and sent to the main circuit 1-1. Thereby, the main circuit 1-1 controls the opening and closing of the control valve 5B based on the value of the current converted by the fixed resistor 1-4, that is, the value of the DC voltage signal V.

  However, in this positioner 1B, since the resistance value r of the fixed resistor 1-4 is large, the impedance with respect to the AC voltage signal Vf on the input line is too high compared to the power supply side, and the converted current is small. It becomes impossible to communicate. Usually, in order to prevent the communication signal from entering the power supply side on the power supply side, the impedance Zf is medium with respect to the communication signal (AC electrical signal), and the DC signal (DC electrical signal). Although the communication filter 6 having an impedance characteristic in which the impedance Zdc is extremely low is provided, even if such a communication filter 6 is provided, communication is not possible because Zf << r.

  The present invention has been made to solve such a problem, and the object of the present invention is to provide an inexpensive configuration capable of performing communication with a simple change to a general current input type positioner. The object is to provide a voltage input type positioner.

  In order to achieve such an object, the present invention receives a direct current electric signal from a host system via a pair of electric wires and generates its own operating power supply from the direct current electric signal, while the direct current electric signal is generated. In the positioner that controls the opening degree of the control valve according to the value of the current input type communication circuit that receives the AC electrical signal superimposed on the DC electrical signal from the host system, and the communication circuit When the DC electrical signal from the host system is a voltage, the voltage-current converter circuit converts the voltage to a current and sends it to the communication circuit. The impedance is high, and the impedance to the AC electrical signal is lower than the impedance to the DC electrical signal.

  According to the present invention, when an AC voltage signal (AC electrical signal) is sent from the host system superimposed on a DC voltage signal (DC electrical signal), the voltage-current conversion circuit The signal is converted into a direct current signal with a high impedance, and the alternating voltage signal is converted into an alternating current signal with a low impedance. The alternating current signal converted by the voltage-current converter circuit is sent to a current input type communication circuit.

  The voltage-current conversion circuit according to the present invention can be configured by a parallel circuit of a capacitor and a resistor, or can be configured by a parallel circuit of a series circuit of an inductance and a capacitor and a resistor.

  Further, a bypass circuit may be connected in parallel to the voltage / current conversion circuit, and a changeover switch that enables / disables the parallel connection of the bypass circuit to the voltage / current conversion circuit may be provided. In this case, if the parallel connection of the bypass circuit to the voltage-current conversion circuit is enabled, the voltage-current conversion circuit does not function and a current input type positioner is obtained.

  According to the present invention, the voltage-current conversion circuit having the characteristic that the impedance to the DC electrical signal is high and the impedance to the AC electrical signal is low is provided in the previous stage of the communication circuit. The AC voltage signal is converted into an AC current signal as it is due to the low impedance, and communication can be performed with a simple change to a general current input type positioner. Therefore, it is possible to provide a voltage input type positioner having an inexpensive configuration.

It is a figure which shows the structure of the principal part of the system using one Embodiment (Embodiment 1) of the positioner which concerns on this invention. It is a figure which shows the specific example of the voltage current conversion circuit provided in the front | former stage of the communication circuit of the positioner in this system. It is a figure which shows the frequency characteristic of the impedance Z in the specific example of this voltage current conversion circuit. It is a figure which shows the example (Embodiment 2) which provided the bypass circuit via the switch in parallel with the voltage current conversion circuit. It is a figure which shows the example which turned on the changeover switch in the bypass circuit provided in parallel with the voltage current conversion circuit, and was used as a current input type positioner. It is a figure which shows the structure of the principal part of the system using the positioner (general current input type positioner) which has a communication function between high-order systems. It is a figure which shows the example which provided the fixed resistor in the front | former stage of the communication circuit of the current input type positioner, and tried to change into the voltage input type positioner.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[Embodiment 1]
FIG. 1 is a diagram showing a configuration of a main part of a system using an embodiment (Embodiment 1) of a positioner according to the present invention. In this figure, the same reference numerals as those in FIG. 7 denote the same or equivalent components as those described with reference to FIG.

  In this system, as can be seen in comparison with the system shown in FIG. 7, a voltage-current conversion circuit 1-5 is provided in the positioner 1 (1C) instead of the resistor 1-4. The voltage-current conversion circuit 1-5 has an impedance characteristic that the impedance Z is extremely low with respect to a communication signal (AC electrical signal) and the impedance Zsig is high with respect to a DC signal (DC electrical signal). Have.

  FIG. 2 shows a specific example of the voltage-current conversion circuit 1-5. The voltage / current converter 1-5 shown in FIG. 2A is a parallel circuit of a capacitor C and a resistor R. The voltage-current conversion circuit 1-5 shown in FIG. 2B is a parallel circuit of a series circuit of an inductance L and a capacitor C and a resistor R.

  In this positioner 1C, the DC voltage signal V from the host device 2B is converted into a current with an impedance Zsig in the voltage-current conversion circuit 1-5, that is, converted into a current with an impedance Zsig that is higher than the DC signal, and the main circuit 1-1. Thereby, the main circuit 1-1 controls the opening and closing of the control valve 5B based on the value of the current converted by the voltage-current conversion circuit 1-5, that is, the value of the DC voltage signal V.

  Further, in this positioner 1C, the AC voltage signal Vf from the communication device 3B is converted into a current with an impedance Z in the voltage-current conversion circuit 1-5, that is, converted into a current with an impedance Z that is extremely low with respect to the communication signal. And sent to the current input type communication circuit 1-2. In this case, since Zf >> Z, the intrusion of the communication signal to the power source side is prevented, and the AC voltage signal Vf is converted into an AC current signal as it is in the voltage-current conversion circuit 1-5. It is converted and sent to the current input type communication circuit 1-2.

  FIG. 3A shows the frequency characteristics of the impedance Z in the voltage-current conversion circuit 1-5 shown in FIG. FIG. 3B shows frequency characteristics of the impedance Z in the voltage-current conversion circuit 1-5 shown in FIG. In the voltage-current conversion circuit 1-5 shown in FIG. 2A, as shown in FIG. 3A, by setting the values of the capacitor C and the resistor R appropriately, a predetermined value including the communication frequency fcom is set. The impedance Z can be made extremely low with respect to the above frequency. In the voltage-current conversion circuit 1-5 shown in FIG. 2B, the communication frequency fcom is set by appropriately setting the values of the capacitor C, the resistance R, and the inductance L as shown in FIG. 3B. The impedance Z can be extremely low as the center.

  As can be seen from the above description, the positioner 1C according to the first embodiment is a voltage current constituted by CR or CRL in the preceding stage of the communication circuit 1-2 of the general current input type positioner 1A shown in FIG. By only providing the conversion circuit 1-5, the AC voltage signal Vf from the communication device 3B can be received, and communication with the communication device 3B becomes possible. In this manner, in the present embodiment, it is possible to provide a voltage input type positioner 1C having an inexpensive configuration capable of performing communication with a simple change to a general current input type positioner 1A.

[Embodiment 2]
The positioner 1C shown in FIG. 1 is used as a voltage input type positioner. In order to make the positioner 1C into a current input type, the voltage-current conversion circuit 1-5 must be removed. Therefore, in the second embodiment, as shown in FIG. 4, a bypass circuit (short circuit) 1-6 is provided in parallel with the voltage-current conversion circuit 1-5, and the changeover switch 1 is provided in the bypass circuit 1-6. -7 is provided.

  When this positioner 1 (1D) is used as a voltage input type positioner, the selector switch 1-7 is turned off as shown in FIG. As a result, the parallel connection of the bypass circuit 1-6 to the voltage / current conversion circuit 1-5 is invalidated, and the voltage / current conversion circuit 1-5 functions to be a voltage input type positioner.

  On the other hand, when the positioner 1D is used as a current input type positioner, the selector switch 1-7 is turned on as shown in FIG. As a result, the parallel connection of the bypass circuit 1-6 to the voltage / current conversion circuit 1-5 is enabled, the voltage / current conversion circuit 1-5 does not function, and a current input type positioner is obtained.

  In the first and second embodiments, the control valve 5B is an electromagnetic valve. However, the power supply system to the positioners 1C and 1D is a field bus system, and the control valve 5B is a proportional valve. Good.

  In the first and second embodiments, the communication device 3 is connected between the transmission lines L1 and L2 as necessary. However, in the system in which communication is performed between the host device 3 and the positioner 1. There may be.

  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 (1A-1D) ... Positioner, 1-1 ... Main body circuit, 1-2 ... Communication circuit, 1-3 ... Constant voltage circuit, 1-4 ... Resistance, 1-5 ... Voltage-current conversion circuit, 1-6 ... Bypass circuit, 1-7 ... changeover switch, 2 (2A, 2B) ... host device, 3 (3A, 3B) ... communication device, 4 ... host system, 5 (5A, 5B) ... control valve, 6 ... communication filter , L1, L2 ... transmission path (a pair of electric wires), R ... resistance, C ... capacitor, L ... inductance.

Claims (4)

Receives a DC electrical signal from the host system via a pair of electric wires, generates its own operating power supply from this DC electrical signal, and controls the opening of the control valve according to the value of the DC electrical signal In the positioner,
A current input type communication circuit that receives an AC electrical signal transmitted from the host system superimposed on the DC electrical signal; and
Provided in the previous stage of the communication circuit, when the DC electrical signal from the host system is a voltage, comprising a voltage-current conversion circuit that converts this voltage into a current and sends it to the communication circuit,
The voltage-current conversion circuit has a characteristic that an impedance with respect to the DC electric signal is high and an impedance with respect to the AC electric signal is lower than an impedance with respect to the DC electric signal. The positioner as claimed in claim 1,
A bypass circuit connected in parallel to the voltage-current converter circuit;
A positioner comprising: a changeover switch for enabling / disabling parallel connection of the bypass circuit to the voltage-current conversion circuit. The positioner according to claim 1 or 2,
The voltage-current conversion circuit is a parallel circuit of a capacitor and a resistor. The positioner according to claim 1 or 2,
The voltage-current conversion circuit is a parallel circuit of a series circuit of an inductance and a capacitor and a resistor.

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