JPH10281101A - Electric-pneumatic converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To hold an air pressure even while an input signal is off and a power source is off and prevent the occurrence of a plant trouble. SOLUTION: At an external control part 4, an input signal from a controller 11 is compared with an input signal during preceding sampling of a preceding data memory part 12 by a comparing part 13. A differential output therebetween is superimposed on a voltage from a power source 16 by a superimposing circuit 14 and fed to a body part 2 through a two-wire 3. In the body part 2, a superimposing signal is received by a signal receiving circuit 26, and a motor drive circuit 27 to receive the superimposing signal drives a motor 28, a nozzle flapper 29 is displaced, and an air pressure responding to an input signal from a servo relay 30 is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electropneumatic converter that changes air pressure in response to an electric signal (such as a current signal) from a control system such as a plant.

[0002]

2. Description of the Related Art A well-known conventional electropneumatic converter is shown in FIG.
As shown in the figure, two lines 3 from the controller 11 of the external control panel 1
Thus, the main body 2 receives a current signal of, for example, 4 to 20 mA. In the main body 2, an electromagnetic force is applied to the armature 22 by the input signal current flowing through the coil 21, and the electromagnetic force changes the back pressure of the nozzle flapper 23. The pilot pressure is driven by this back pressure change to change the air pressure. The air pressure of the pilot valve 24 is applied to the armature 22 as a feedback signal via the restoration bellows 25.

[0003]

In the above-described conventional electropneumatic converter, when the input signal is cut off, no current flows through the coil, so that no electromagnetic force can be applied to the armature and the state of the noise flapper is reduced. Can not hold, can not hold air pressure. Therefore, there is a problem in that the output air pressure greatly changes and adversely affects the state of the plant.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an electropneumatic converter which can maintain air pressure even when an input signal is cut off or a power supply is cut off, and can prevent plant trouble. Aim.

[0005]

An electropneumatic converter according to the present invention comprises an external control unit and a main unit, and changes an air pressure according to an electric signal.
The main unit includes a comparison unit that compares a signal input at the time of sampling this time with a signal input at the time of previous sampling, and a superimposition unit that superimposes a signal corresponding to the comparison of the comparison unit on a power supply line. An acquisition unit that determines and acquires a superimposition signal from the superimposition unit, and an air pressure control drive unit that increases and decreases the air pressure with the acquired signal, and connects the external control unit and the main unit with two wires. In the main body, the air pressure is changed only when the superimposed signal is transmitted, and when the superimposed signal is not transmitted, or when the power is turned off, the air pressure according to the signal transmitted last time is maintained. ing.

According to the electropneumatic converter, the input signal at the time of the current sampling and the signal input at the time of the previous sampling are compared by the comparing unit of the external control unit, and the output of the comparing unit and the power supply line are compared by the superposition unit. Are superimposed and sent to the main body via two wires. The main unit acquires the superimposed signal sent by the acquisition unit and supplies it to the air pressure control unit. The air pressure control unit increases / decreases the air pressure according to the acquired signal. When the superimposed signal is not sent or when the power is turned off, the air pressure is kept at the air pressure corresponding to the signal sent last time. When the input signal is interrupted, the air pressure is maintained at the previous value even when the power is interrupted, so that plant trouble can be prevented.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to embodiments. FIG. 1 is a block diagram showing a configuration of an electropneumatic converter according to an embodiment of the present invention. The electropneumatic converter according to this embodiment includes an external control unit 4 provided on a control panel 1 and a main body unit 2 connected to the external control unit 4 by two wires 3.
It is composed of The external controller 4 includes a controller 11
Data storage unit 12 for receiving and storing an input signal at the time of sampling, and a comparing unit 1 for receiving an input signal at the time of current sampling from the controller 11 and comparing with the previous data.
3, an output of the comparator 13, a superimposing circuit 14 for superimposing the supply voltage from the power supply 16, and an answerback signal acquiring circuit 15 for acquiring an answerback signal from the main body 2 and feeding it back to the controller 11. Have.

The main body 2 includes a signal acquisition circuit 26 for receiving a superimposed signal sent via the two wires 3, a motor drive circuit 27 for receiving the acquired signal and driving a motor,
8, a nozzle flapper 29, a servo relay 30, an air pressure sensor 31 that converts the air pressure of the servo relay 30 into an electric signal and feeds back the electric signal, and an answer back signal superimposing circuit 32.

Next, the overall operation of the electropneumatic converter of this embodiment will be described. The signal input from the control unit 11 of the control panel 1 installed in the plant or the like to the external control unit 4 is compared by the comparator 13 with the signal input at the time of the previous sampling, and a difference signal is obtained. D _i-1 the% data of the preceding sampling i-1 point, the% data of the current sampling i point When D _i, the difference signal is D _i -D _i-1.

The difference signal is input to the superposition circuit 14,
The superposition circuit 14 outputs a signal corresponding to the difference signal to the power supply 16.
Power supply signal to the main unit 2
At the same time it is supplied by two wires 3. Here, the signal corresponding to the difference signal
Is, for example, a difference signal = D _i-D_i-1= + N% difference
If there are, n pulses as shown in FIG.
D_i-D_i-1= −n%, if (b) in FIG.
Are n pulses as shown in FIG.

In the main unit 2, when a superimposed signal is sent from the two wires 3, the signal acquisition circuit 26 determines and acquires the superimposed signal. The power signal is used as it is for power supply of each unit of the main body 2. The superimposed signal acquired by the signal acquisition circuit 26 is applied to a motor drive circuit 27. The motor drive circuit 27 calculates a difference between the two signals based on this signal and a signal corresponding to the output air pressure fed back from the air pressure sensor 31. Is driven to adjust the distance between the nozzle flags 10 of the nozzle flapper 29 to adjust the air pressure output from the servo relay 30.

The output air pressure is converted into an electric signal by an air pressure sensor 31 and supplied again as a feedback signal to a pulse motor drive circuit 27 to drive the motor 28 and to set an appropriate distance between the nozzle flapper according to the input signal. Guide to position. The output electric signal of the air pressure sensor 31 is simultaneously superimposed again on the power supply line by the answer back signal superimposing circuit 32 as an answer back signal, and is answer backed to the external control unit via the two wires 3. The answer-backed signal is converted into a signal of, for example, 4 to 20 mA and returned to the controller 11 such as a plant.

In this embodiment, if the comparison signal of the comparison unit in the external control unit is zero, no signal is given to the drive system. Therefore, a drive unit such as a pulse motor that can maintain the distance between the nozzle flapper even when no signal is given or when the power is turned off is used. In addition,
In the above embodiment, the pulse signal is superimposed on the power supply line, but a serial communication signal or a sine waveform signal may be superimposed.

[0014]

According to the present invention, it is possible to maintain the air pressure even in the event of a trouble such as a power supply cutoff or an input signal cutoff, thereby minimizing plant troubles. If the comparison signal in the external control unit is zero, no signal is given to the drive system, so that the current consumption is small.

It is possible to realize a two-wire instrument which does not require construction such as external power supply wiring at the site where the main body is installed. Existing wiring can be used as it is, and replacement from conventional products is easy. The signal from the controller can be supplied as a standard unified signal, and no special signal converter is required (any manufacturer).

There are the following effects.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electropneumatic converter according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a superimposed signal in the electropneumatic converter of the embodiment.

FIG. 3 is a block diagram showing a conventional electropneumatic converter.

[Explanation of symbols]

 2 Body part 3 Two wires 4 External control part 11 Control part 12 Previous data storage part 13 Comparison part 14 Superposition circuit 16 Power supply 26 Signal acquisition circuit 27 Motor drive circuit 28 Motor 29 Nozzle flapper 30 Servo relay

Claims (1)

[Claims] An electro-pneumatic converter comprising an external control unit and a main body unit, the air-pressure converter changing air pressure in accordance with an electric signal, wherein the external control unit receives a signal input at the time of sampling this time and a signal input at the time of previous sampling. And a superimposing unit that superimposes a signal corresponding to the comparison of the comparing unit on a power supply line. The main body unit determines and acquires a superimposed signal from the superimposing unit. An acquisition unit and an air pressure control drive unit that increases and decreases the air pressure based on the acquired signal, and connects the external control unit and the main unit with two wires, and when a superimposed signal is sent from the main unit Change the air pressure only when the superimposed signal is not sent,
Alternatively, an electropneumatic converter characterized in that when power is turned off, an air pressure according to a signal sent last time is maintained.