JPH0526322Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an electropneumatic positioner that obtains a valve opening corresponding to a current signal, and particularly relates to an improvement of a transmission circuit that transmits a valve opening signal.

<Prior Art> FIG. 2 is a block diagram showing an outline of the structure of an electro-pneumatic positioner disclosed in Japanese Patent Application No. 1988-213799 entitled "Electro-pneumatic positioner".

10 and 11 are for example 4 to 4 from a controller etc.
This is an input terminal that receives current output I _p such as 20 mA as input current I _p . 12 is an input processing circuit;
Resistor 1 inserted in series between input terminals 10 and 11
21 converts the input current I _p into a voltage signal V _i , and a Zener diode 12 connected in series with this resistor.
Step 2 creates the circuit power supply voltage E _b .

A differential amplifier 13 amplifies the difference between the voltage signal V _i and the feedback signal V _f . The piezoelectric actuator 16 that displaces the flapper 168 is differentially driven by the differential voltage V _c between the output V _p of the differential amplifier 13 and the feedback signal V _p related to the stem displacement of the pilot relay 14 .

The piezoelectric actuator 16 includes piezoelectric elements 161,1
62, and these piezoelectric elements are driven differentially by a differential voltage V _c and are displaced in opposite directions. A nozzle 17 is arranged opposite the flapper 168, and the nozzle back pressure _Pb of the nozzle 17 changes in accordance with the differential voltage _Vc , which is input to the pilot relay 14.

The pilot relay 14 amplifies the nozzle back pressure P _b and converts it into a pneumatic output P _p .
Displace. This displacement is converted into a feedback signal V _p by the displacement/electrical signal converter 19, and the differential amplifier 13
The difference between the output V p and the output V _p is taken.

The valve 20 connects the pneumatic output P _p to the valve stem 20
1, and this displacement is converted into a feedback signal V _f by a displacement/electrical signal converter 21. This displacement/
The electric signal converter 21 is constructed using a vibrating force sensor, and a pair of piezoelectric elements 213 and 214 are arranged on an etched vibrating part 212 of a cantilever beam 211 with one end fixed. The two piezoelectric elements form a closed loop to cause the vibration section 212 to self-oscillate at its natural frequency.
By converting the displacement X of the valve stem 201 into force and inputting it to the other end of the cantilever beam 211 via a spring 216, a frequency output _o related to the displacement X of the valve stem 201, that is, the valve opening degree can be obtained. I can do it. The frequency output _o of the amplifier 215 is converted into a feedback signal V _f by the frequency/voltage conversion circuit 217 and fed back to the differential amplifier 13 .

The above is the configuration of the main body 22 of the conventional electro-pneumatic positioner. In addition, the transmission section 23 described below is also included.
is connected.

The transmission circuit 24 receives the feedback voltage V _f and outputs a current output I _v of 4 to 20 mA corresponding to the span of the feedback voltage V _f to output terminals 25 and 26 . One ends of two-wire transmission lines l ₁ and l ₂ are connected to the output terminals 25 and 26 .

A receiving circuit 27 is provided at the other end of the transmission lines l ₁ and l ₂ .
and a power supply 28 are connected, and the power supply 28 supplies power to the transmission circuit 24, and the transmission circuit 24 supplies a current corresponding to the feedback signal V _f to the reception circuit 27.

<Problems to be Solved by the Invention> However, the electropneumatic positioner with this conventional configuration, in addition to the Zener diode that generates the circuit voltage E _b of the main body 22, also has a valve 20 connected to the valve 20 at a position away from the main body 22. There is a problem in that a separate external power source 28 is required for the transmission section 23 installed to determine the valve opening degree.

<Means for Solving the Problems> In order to solve the above problems, the present invention transmits a current signal from two transmission lines and converts the current signal into a circuit power supply and a current signal necessary for circuit operation. Obtain a corresponding voltage signal, displace the stem of the valve with an output signal corresponding to the difference signal between the voltage signal and the feedback signal, and use a signal related to the frequency signal corresponding to this displacement as a feedback signal to control the valve corresponding to the current signal. An electro-pneumatic positioner for determining the opening is provided with a superimposition circuit that is supplied with voltage from a circuit power source and superimposes a valve opening signal on a transmission line that corresponds to a frequency signal and can be distinguished from a current signal.

<Operation> Since the valve stem displacement is converted into a frequency signal and a signal related to this frequency signal is returned to the input side as a feedback signal, this frequency signal is used to control the superimposition circuit energized by the circuit power supply. According to
The current output flowing through two transmission lines is a frequency signal or a digital signal that is superimposed on the current output and sent to the transmission line, and is generated at both ends of a resistor inserted in series with the transmission line. The valve opening degree of the valve is detected by restoring the signal or digital signal. Therefore, the opening degree of the valve can be known on the transmitting side without having to prepare a power source separate from the power source for the main body.

<Example> Hereinafter, an example of the present invention will be described using the drawings. FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention. Note that parts having the same functions as those of the conventional electropneumatic positioner shown in FIG. 3 are designated by the same reference numerals, and the description thereof will be omitted as appropriate.

The differential amplifier 13 has a voltage signal V _i applied to its non-inverting input terminal (+) via a resistor 30, a feedback signal V _f being applied to its inverting input terminal (-), and amplifies these difference signals. do. And this differential amplifier 1
A capacitor 31 is connected between the non-inverting input terminal (+) and the inverting input terminal (-) of No. 3, and the resistor 30 and capacitor 31 constitute a low-pass filter 32.

The difference between the output V _p of the differential amplifier 13 and _the feedback signal V _p is calculated and output as a change in the nozzle back pressure P _b of the nozzle 17 via the actuator 16 . It is amplified and the valve stem 201 of the valve 20 is displaced X
let

_{This displacement}
The signal is fed back to the differential amplifier 13 as a signal.

The frequency output _o is a signal proportional to the displacement X of the valve stem 201. This frequency output _o is input to the superimposition circuit 33, where it is converted into a voltage pulse V _o corresponding to the frequency output _o and output to the transmission line _l2 .

This superimposition circuit 33 includes transistors 331, 33
2, resistor 333, 334, 335, capacitor 3
It is composed of 36 mag. One end of the series circuit in which the resistor 333, the emitters and collectors of the transistors 331 and 332, and the resistor 334 are connected in series is connected to the common potential point COM, and the other end is connected to the Zener diode 122, where the power supply voltage is connected.
E _b is applied. Transistors 331 and 3
A frequency output _o is applied to the base of 32, and a voltage pulse V _o corresponding to the frequency output _o is outputted from the collectors of these through a resistor 335 and a capacitor 336 to the transmission line l ₂ .

In this way, the voltage pulse V _o is superimposed on the input current I _p on the transmission lines l ₁ and l ₂ and transmitted to the adjustment measurement. Therefore, in the control measurement, that is, on the panel instrument side, by inserting a receiving resistor R in series with the transmission lines l ₁ and l ₂ , it is possible to receive the pulse signal generated at both ends of the transmission lines l 1 and l 2 . Since this pulse signal corresponds to the valve opening degree, the valve 20 can be connected to the panel instrument side (transmission side) without any special power supply.
The valve opening degree can be detected.

On the other hand, a diode 34 is inserted in series with the input terminal 11 on the transmission line _l2 side so that the polarity is opposite to that of the input current I _p , and a voltage pulse V _o is applied between this and the input terminal 11, and Since the low-pass filter 32 is inserted at the input end of the differential amplifier 13, the differential amplifier 13 is not affected by the frequency output _o .

Note that in the embodiment shown in FIG. 1, the valve opening degree of the valve 20 is detected by a vibration type sensor and converted into a frequency, but the invention is not limited to this, and for example, a magnetostrictive potentiometer,
A frequency signal or
By converting to a PWM signal, it can be applied in the same way as shown in FIG.

<Effects of the invention> As described above in detail with the embodiments, according to the invention, a signal proportional to the valve opening of the valve can be transmitted from
It can be detected on the 20mA generation side, that is, on the panel instrument side.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention, and FIG. 2 is a block diagram showing the configuration of a conventional electropneumatic positioner. 12...Input processing circuit, 13...Differential amplifier,
14... Pilot relay, 16... Actuator, 19, 21... Displacement/electrical signal converter, 2
0... Valve, 22... Main body, 23... Transmission section, 24... Transmission circuit, 32... Low-pass filter,
33... Superposition circuit, V _f ... Feedback signal, V _o ... Voltage pulse, _o ... Frequency output, X... Displacement.

Claims (1)

[Scope of utility model registration request] A current signal is transmitted from the two transmission lines, and from this current signal, a circuit power supply necessary for the operation of the circuit and a voltage signal corresponding to the current signal are obtained, and an output corresponding to the difference signal between the voltage signal and the feedback signal is obtained. In an electro-pneumatic positioner that displaces a valve stem in response to a signal and uses a signal related to a frequency signal corresponding to this displacement as the feedback signal to obtain a valve opening corresponding to the current signal, a voltage is supplied from the circuit power supply and the An electro-pneumatic positioner comprising a superimposition circuit that superimposes a valve opening signal on the transmission line that corresponds to the frequency signal and can be distinguished from the current signal.