JPH06249201A - Positioner - Google Patents

Abstract

PURPOSE:To eliminate generation of any drift in a valve opening near the valve opening target value. CONSTITUTION:In a control unit 20, a valve opening setting signal is received from an outer controller, and an electropneumatic conversion unit is controlled by feed back of an opening position signal from a position sensor 25. After the deviation between the set opening and a valve real opening comes in a prescribed range, feed back control is carried out by an air pressure signal from a pressure sensor 27 for detecting an output pressure to the driving unit 24 of a pilot valve 23. Since there is no influence of frictional resistance of a valve seal packing, any drift in a valve opening is eliminated when the valve opening comes near the set opening, and also responsiveness can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positioner for adjusting the opening of a control valve such as the flow rate of fluid.

[0002]

2. Description of the Related Art As a conventional positioner for adjusting the opening of a control valve of this type, there is a positioner as shown in FIG. This positioner controls the air pressure from an external pressure supply source in response to a control signal from the control unit 30 that receives a valve opening setting signal for setting the valve opening from an external controller, and outputs the signal. An electro-pneumatic conversion unit 31, a drive unit 34 that drives the valve 8 by the controlled air pressure, and a position sensor 35.
The output of the position sensor 35 is fed back to the control unit 30 via the A / D converter 36.

FIG. 5 shows an example of the layout of the drive unit and the position sensor. The drive unit 34 having a diaphragm (not shown) inside the valve body 40 and the frame 37.
The diaphragm and the valve body in the valve body are connected by a stem 38 so that the displacement of the diaphragm is transmitted to the valve body. The position sensor 35 is composed of a rotary potentiometer 41 having a lever 39, is supported by a frame 37, and the lever 39 is provided with a pin 42 provided on a stem 38.
It is connected with. As a result, as shown in (b) of the figure, the position sensor outputs the displacement of the stem 38 represented by the pin position y as a signal representing the angular position θ.

In this positioner, the control unit 30 outputs a control signal to the electropneumatic conversion unit 31 in response to the valve opening setting signal R. In the electro-pneumatic conversion section 31, the air pressure supplied from the pneumatic pressure source is adjusted according to the control signal, and the drive section 34 is adjusted.
Send to. The drive unit 34 receives the air pressure and stroke-displaces the stem 38 to change the opening degree of the valve. When the valve opening control is performed in this manner, the position sensor 35 detects the lever angle and outputs the detected value as A /
It is sent to the control unit 30 via the D converter 36. The control unit 30 obtains the deviation between the target value and the current value at this angular position and performs Gap type PID control.

[0005]

In the above PID control,
Although the deviation is given while setting the target in multiple stages, in the above-mentioned conventional positioner, a deviation of about 0.1 to 0.5% occurs after the deviation from the final target value is within 1%. It was the reality. This phenomenon is particularly likely to occur when the operation of the stem is not smooth due to the frictional resistance of the seal packing in the valve or the drive unit because the integral gain in Gap is increased from the viewpoint of efficiency. Therefore, the present invention
In view of the above conventional problems, it is an object of the present invention to provide a positioner in which fluctuation does not occur near the valve opening target value.

[0006]

Therefore, the present invention is based on FIG.
As shown in FIG. 3, the control means 1 to which the valve opening setting signal is input, the electro-pneumatic conversion means 6 that outputs the air pressure controlled according to the control signal from the control means 1, and the valve by the controlled air pressure. In the positioner including the driving means 7 for driving the driving means 8, the opening degree detecting means 9 for outputting a position signal corresponding to the opening degree of the valve 8 and the pressure for detecting the air pressure to the driving means 7 and outputting the air pressure signal. The detection means 10 is provided, and the control means 1 includes a comparison means 4 for comparing a valve opening setting signal and a position signal, and a first control calculation means 2 for calculating a control value by feedback control using the position signal.
A second control calculation means 3 for calculating a control value by feedback control using an air pressure signal, and a switching means 5 for switching the outputs of the first and second control calculation means.
When the deviation between the valve opening setting signal and the position signal is equal to or larger than a predetermined width, the output of the first control calculation means 2 is used as the control signal, and when the deviation is within the predetermined width, the second control calculation means The output of 3 is used as the control signal.

[0007]

The difference between the set opening based on the valve opening setting signal and the actual opening of the valve detected by the opening detection means 9 is checked by the comparison means 4. While the deviation is equal to or larger than the predetermined width, the first control calculation unit 2 performs the control calculation by the feedback of the opening position signal from the opening detection unit 9, and the control signal is output via the switching unit 5. The output of the control means 1 is sent to the electropneumatic conversion means 6. When the deviation falls within the predetermined range, the switching means 5 outputs the control signal of the second control calculation means 3 as the output of the control means 1. The second control calculation means 3 performs control calculation by feedback control using the air pressure signal from the pressure detection means 10 and outputs a control signal. Here, since the opening position signal is not used, control is performed that is not affected by the friction resistance of the seal packing of the valve.

[0008]

FIG. 2 is a diagram showing an embodiment of the present invention. A valve opening setting signal R for setting the valve opening is input to the control unit 20 from an external controller. An electro-pneumatic conversion section 21 that controls and outputs air pressure from an external pressure supply source in accordance with a control signal from the control section 20 is provided, and an output of a pilot valve 23 that receives the control pressure from the electro-pneumatic conversion section 21 The drive unit 24 drives the valve 8.

A position sensor 25 as an opening detecting means is attached to the valve 8, and the position sensor 25
Is fed back to the control unit 20 via the A / D converter 26. Further, a pressure sensor 27 that detects the output pressure of the pilot valve 23 is provided, and the detection output of the pressure sensor 27 is the A / D converter 28.
It is adapted to be input to the control unit 20 via.

FIG. 3 shows the flow of processing in the control unit 20. First, at step 101, a valve opening setting signal R for setting the valve opening is input from an external controller, and at step 102, the output of the position sensor 25 is input via the A / D converter 26. In step 103, the deviation e between the set opening based on the valve opening setting signal R and the actual opening which is the feedback signal from the position sensor 25 is checked.

Here, while the deviation e is within a predetermined width Pe, for example, 1% or more, the routine proceeds to step 104, where the deviation is included in a variable to perform PID control, and the input valve opening setting is performed. A control value is calculated corresponding to the signal in the direction of reducing the deviation, and a control signal to the electropneumatic conversion unit 21 is output. When the deviation is smaller than the predetermined width Pe in the check in step 103, the process proceeds to step 105,
The pressure value of the pilot valve 23 at that time input from the pressure sensor 27 via the A / D converter 28 is stored.

Thereafter, in step 106, a control value is calculated using the detection output of the pressure sensor 27 as a feedback signal so that the output pressure of the pilot valve 27 is held at the stored pressure value, and the control value is output. To be done. Steps 101 to 102 and 104 constitute the first control calculation means of the invention, and steps 105 to 106 are the second.
It constitutes the control calculation means of. Further, step 103 serves both as a comparison means and a switching means.

This embodiment is configured as described above, and in controlling the valve opening, first, feedback control is performed by the opening position signal from the position sensor, and the deviation from the set opening based on the valve opening setting signal is detected. After entering the specified range, the pressure sensor measures and stores the pilot valve output pressure at that time to maintain the output pressure, so it is not affected by the friction resistance of the valve seal packing. There is an effect that the responsiveness is improved as a result of eliminating the wobbling after becoming close to the set opening degree and by reducing the control time until the valve opening degree is settled.

In the embodiment, the air pressure to the driving means is detected by the pressure sensor for detecting the pilot valve output pressure, but the invention is not limited to this. For example, the output pressure of the electropneumatic conversion section for driving the pilot valve is detected. Then, it can also be used for pressure feedback in the vicinity of the target set opening. Furthermore, the type of position sensor is not particularly limited.

[0015]

As described above, according to the present invention, in addition to the opening detecting means for detecting the actual opening position of the valve, the pressure detecting means for detecting the air pressure to the driving means is provided, and the set opening and the actual valve opening are provided. Feedback control using the actual opening position signal is performed until the deviation from the opening falls within the specified range, and after the deviation enters the specified range, feedback control using the air pressure signal is switched to. It has the effect of eliminating fluctuations when the opening is near the set opening and improving responsiveness.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of the present invention.

FIG. 2 is a diagram showing an embodiment of the invention.

FIG. 3 is a flowchart showing a processing flow in the embodiment.

FIG. 4 is a diagram showing a conventional example.

FIG. 5 is a diagram showing a layout of a drive unit and a potentiometer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 control means 2 1st control calculation means 3 2nd control calculation means 4 comparison means 5 switching means 6 electropneumatic conversion means 7 drive means 8 valve 9 opening degree detection means 10 pressure detection means 20 control section 21 electropneumatic conversion section 23 Pilot valve 24 Drive part 25 Position sensor 26, 28 A / D converter 27 Pressure sensor 30 Control part 31 Electro-pneumatic conversion part 34 Drive part 35 Position sensor 36 A / D converter 37 Frame 38 Stem 39 Lever 40 Valve body 41 Potentiometer 42 Pin R Valve opening setting signal

Claims (1)

[Claims] 1. A control means to which a valve opening setting signal is inputted, an electropneumatic converting means for outputting an air pressure controlled according to the control signal from the control means, and a valve driven by this controlled air pressure. In a positioner having a driving means for operating, an opening degree detecting means for outputting a position signal corresponding to the opening degree of the valve, and a pressure detecting means for detecting the air pressure to the driving means and outputting an air pressure signal, The control means is controlled by comparing means for comparing the valve opening setting signal with the position signal, first control calculating means for calculating a control value by feedback control using the position signal, and feedback control using the air pressure signal. It comprises a second control calculation means for calculating a value and a switching means for switching the outputs of the first and second control calculation means. No. 1 when the deviation of the number is more than a predetermined width
The positioner is configured so that the output of the control calculation means of is the control signal, and the output of the second control calculation means is the control signal when the deviation falls within a predetermined range.