JPH0298603A - Positioner - Google Patents

Abstract

PURPOSE:To foresee the fault of a valve and to preserve by providing a variable impedance element, the impedance of which is varied in accordance with the valve opening degree, in series to a magnet unit and transmitting the valve opening degree to a controller. CONSTITUTION:An input current sent from the controller 16 is converted to a force F1 by the magnet unit 21 and the force is given to a beam 22. A displacement is generated in the beam 22 by the force F1 received and a back pressure is given to a nozzle 23. This back pressure is amplified by a pilot relay 24 and converted to a pneumatic pressure, by which the force FP is given to the beam 22 for its rebalancing, and an air motor for the valve is driven by the output pneumatic pressure to make a valve lift to the upper limit, and yet the displacement of the lift is converted to the turn of a potentiometer 26 as the variable impedance element, conveying through a transmission shaft 27, and a voltage drop VP generated in the potentiometer 26 is transmitted to the controller 10 together with the voltage drop VL of the magnet unit 21. With this arrangement, the valve opening degree can be detected, thereby the fault of the valve is foreseen.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a self-balancing positioner for determining the valve opening of a pneumatic control valve, and particularly to a positioner for monitoring the valve opening.

[Conventional technology]

Generally, the flow rate control system is a negative feedback control system with a closed circuit configuration as shown in FIG. 4, and the flow control valve itself is often of the self-balancing type as shown in FIG. 5.

In FIG. 4, 1 is a subtracter, 2 is a controller, 3 is a flow rate regulating valve, 4 is a controlled object, and 5 is a flow rate detector. Moreover, FIG. 5 is a system diagram showing in detail the flow control valve 3 of FIG. 4, where 6 is a current/air pressure signal converter as a positioner, 7 is a valve, and 8 is a valve lift displacement detector.

In FIG. 4, a signal representing the difference between the value of the setting signal a and the value of the flow rate signal is input to the controller 2;
outputs a valve operation current signal C from the above difference signal. The valve operation current signal C controls the flow rate control valve 3, and the flow rate control valve 3 controls the object to be controlled (here, the flow rate). The flow rate detector 5 detects the controlled object (flow rate) and uses the subtractor 1 as a flow rate signal.
Output to.

In FIG. 5, a current/air pressure signal converter 6 into which a valve operation current signal C is input controls the opening and closing of a valve 7 using air pressure. The displacement of the valve lift according to the opening and closing of the valve is given to the current/pneumatic signal converter 6 by the valve lift displacement detector 8, and the fifth
The system in the figure is automatically balanced.

(Problems to be Solved by the Invention) In the above-mentioned system, only a control output is given to the control valve in response to an input, and the control valve may malfunction or have poor followability to the control output. Control was carried out with complete disregard for the state of the control equipment.This could lead to unexpected accidents due to detection of failures or delays in control speed.In addition, in consideration of these issues, the reliability of control equipment has recently been improved.・Depending on safety needs, predictive maintenance technology that attempts to maintain the flow rate detector 5 and flow control valve 3 before they fail, and technology that aims to improve reliability by making the controller 2 a duplex redundant system The need for such things is increasing, and some of them are being applied.

However, predictive maintenance for failure of flow control valve systems is not performed except in some applications. The current technical level is as follows.

■ Detection of upper and lower limits of valve lift A limit switch detects whether the valve stem is at the upper limit position or lower limit position.

■ A separate valve opening control is provided, and a new 2-wire transmission line is used to transmit the valve opening with a 4 to 20 mA signal.

In the above method (■), economical position sensing can be performed by attaching a limit switch not only to the upper and lower limits but also to any point, but in the end it is only possible to sense the point, and for current use, it is not possible to turn off the valve when a problem occurs. As a sensor, it only has a passive function, such as confirming that the lift is in a predetermined position or on the safe side.

The above method (■) attempts to detect the valve opening using a separate 24.1 type of wiring, but except for special instrumentation examples such as water treatment systems, wiring costs are high and it is especially difficult to control. It is not widely used because it does not require valve opening information (monitoring at one or two points is sufficient).

An object of the present invention is to provide a positioner with a function of transmitting the operating state of a control valve, and to realize this easily and inexpensively.

[Means to solve the problem]

In order to solve these problems, the present invention receives a valve operation current signal from a controller via two signal lines, converts this valve operation current signal into a pneumatic pressure signal, and determines the valve opening of a pneumatic control valve. In a self-balancing positioner that controls
A variable impedance element whose impedance changes depending on the valve opening of the pneumatic control valve is arranged in series with a magnet unit through which a valve operation current signal flows, and the valve opening of the pneumatic control valve is adjusted to a voltage according to the impedance of the variable impedance element. The information is sent to the controller as follows.

[Effect]

In the positioner according to the present invention, the valve opening degree signal is given as a voltage signal to the signal line by the variable impedance element, and by receiving this on the controller side, a signal indicating the valve opening degree of the pneumatic control valve is transmitted.

〔Example〕

FIG. 1 is a system diagram showing a flow control system to which an embodiment of the positioner according to the present invention is applied. In the same figure, IO
is a controller, 20 is a positioner, 11 is a constant voltage circuit, 12 is an operational amplifier as an actuator drive circuit, 13 is a transistor, 14 is a resistor, 15 is a valve opening detection circuit, 21 is a magnet unit through which a valve operation current signal flows, 22 is a beam, 23 is a nozzle, 24 is a viron trirelay, 25 is a feedback bellows, 26 is a potentiometer as a variable impedance element, and 27 is a transmission shaft through which the valve lift from the valve is transmitted. Note that as the variable impedance element, in addition to the potentiometer, a strain gauge, a capacitive element, a magnetoresistive element, etc. may be used.

Next, the operation will be explained. 4 to 20 m sent from the controller 10 to the positioner 20 via 21 transmission lines
The input current A is converted into a force F by the magnet unit 21, which imparts a force to the beam 22. The beam 22 receives this force Fl and is displaced, giving back pressure to the nozzle 23. The back pressure corresponding to this displacement is amplified by the pilot relay 24 provided with an air source as shown by the arrow AR, and is 0.2~
1 kgf/cm" air pressure. This output air pressure is fed to the feedback bellows 25, which applies a force FP to the beam 22 to rebalance the beam 22. The output air pressure is supplied to the valve air motor (Fig. (not shown)
The displacement of the valve lift is transmitted through the transmission shaft 27 and converted into the rotation of the potentiometer 26 as a variable impedance element, and the voltage drop P generated in the potentiometer 26 is the magneto/ It is sent to the controller 10 along with the voltage drop VI of the unit 21.

The valve opening detection circuit 15 of the controller 10 detects VP from the voltage drop vr+vp to know the valve opening. Next, V
The valve opening detection circuit 15 that detects vp from I+VP will be described.

FIG. 2 is a circuit diagram showing the valve opening detection circuit 15.
-33 are operational amplifiers. In FIG. 2, the same or equivalent parts as in FIG. 1 are given the same reference numerals. As mentioned above, the voltage output from the positioner 20 is v r
+vp. Also, the impedance of the resistor 14 is the first
Same as magnet unit 21 in the figure (e.g. 250Ω)
, and a voltage Vl is generated across the resistor 14. Therefore,
Since the collector-emitter voltage of the transistor 13 is almost zero, 2V is applied to the positive terminal of the operational amplifier 31.
A voltage of I+VP exists, and a voltage of vr occurs at its negative terminal. Since the operational amplifier 31 is an amplifier that outputs the difference in voltage between the plus side terminal and the minus side terminal, its output becomes v r +vp. The operational amplifier 32 is a buffer and outputs the voltage VI generated at the positive terminal.

Since the operational amplifier 33 is an amplifier that outputs the difference between input voltages like the operational amplifier 31, its output becomes VP.

In this way, the potentiometer 2 of the positioner 20
6 (see FIG. 1) can be detected, and therefore the valve opening degree can be detected.

FIG. 3 is a system diagram showing a flow control system to which a second embodiment of the positioner according to the present invention is applied.

In the figure, 28 is a proximity sensor that changes impedance according to a signal from the displacement sensor 28a, 29 is a valve opening feedback spring, 30 is a shaft, 34 is an air motor,
35 is a valve, and the air motor 34 and the valve 35 constitute a pneumatic control valve. In FIG. 3, the same or equivalent parts as in FIG. 1 are given the same reference numerals.

Next, the operation will be explained. An input terminal of 4 to 20 mA sent from the controller 10 to the positioner 20 is converted into force Fl by the magnet unit 21, and the beam 22
Give power to. The beam 22 receives this force Fl and is displaced, giving back pressure to the nozzle 23. The back pressure corresponding to this displacement is amplified by the pilot relay 24 supplied with the air source shown by the arrow AR, and the back pressure is amplified to 0. This output air pressure is converted to an air pressure of '2-1 kgf/cm'.
is given, thereby controlling the opening degree of the valve 35. Further, a force FP corresponding to the valve opening degree is applied by the spring 29 via the shaft 30 to rebalance the beam 22. beam 22
The positional displacement of is detected by the displacement sensor 28a, and the proximity sensor 28 controls its impedance based on this detected value. Therefore, as in the case of FIG. 1, a voltage VP corresponding to the valve opening is generated in the proximity sensor 28, and this voltage VP
is transmitted to the controller 10 along with the voltage drop VI of the magnet unit 21, that is, a voltage of V I +VP. Since the detection of voltage VP is the same as in the first embodiment, its explanation will be omitted.

〔Effect of the invention〕

As explained above, the present invention arranges a variable impedance element whose impedance changes depending on the valve opening degree in series with a magnet unit, and transmits the valve opening degree to the controller as a voltage according to the impedance of the variable impedance element. Since the valve opening degree information can be detected on the controller side using the existing two-wire transmission line, there is an effect that predictive maintenance of valve failure can be achieved.

Further, there is no need to install new wiring for this purpose, and it can be realized with a relatively simple configuration, so it is highly effective as an on-site device. Furthermore, it is also possible to transmit information such as temperature and pressure instead of the valve opening degree, which is highly expandable.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing a flow rate control system to which a first embodiment of the positioner according to the present invention is applied, FIG. 2 is a circuit diagram showing a valve opening detection circuit constituting the controller of FIG. 1, and FIG.
The figure is a system diagram showing a flow control system to which the second embodiment of the present invention is applied, FIG. 4 is a system diagram showing a general flow control system,
FIG. 5 is a system diagram showing a flow control valve to which a conventional positioner is applied. 10... Controller, 11... Constant voltage circuit, 12
...Operation amplifier, 13...Transistor, 14...
・Resistor, 15... Valve opening detection circuit, 20... Positioner, 21... Magnet unit, 22... Beam, 23... Nozzle, 24... Pilot relay,
25...Feedback bellows, 26...Potentiometer, 27...Transmission shaft.

Claims (1)

[Claims] The automatic balancing type receives a valve operation current signal from a controller via two signal lines, and converts the valve operation current signal into a pneumatic signal using a current/pneumatic pressure conversion circuit to control the valve opening of a pneumatic control valve. In the positioner, an impedance variable element whose impedance changes depending on the valve opening of the pneumatic control valve is arranged in series with the magnet unit through which the valve operation current signal flows, and the impedance variable element changes the valve opening of the pneumatic control valve. A positioner characterized in that the voltage is transmitted to the controller as a voltage according to the impedance of the element.