JPH07310843A - Valve positioner - Google Patents

Abstract

PURPOSE:To eliminate an influence exercised by the noise of the drive part of a control valve to effect control and friction of a grand packing, to perform smooth operation, and to reduce an excessive amount and perform high speed response precise control. CONSTITUTION:A valve positioner comprises a microprocessor 42 to compute a control signal MVk, by which at least proportional integrating operation is effected, from a set value signal SV from a master controller 1 and a feedback signal PV from a control valve 3; an electric/pneumatic converting part 44 to convert the control signal MVk into an analogue signal and an operation pneumatic signal 3B; and angle detecting parts 46 and 47 to convert a valve opening signal 3C from the control valve 3 into an angle signal 3D and perform feedback of a valve opening signal, being a digital signal, to the microprocessor 42. This constitution changes a control parameter by which proportional integrating operation is effected according to polarity of a control deviation consisting of a difference between the set value signal SV and the feedback signal PV.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a valve positioner which controls a diaphragm type control valve used in process control, lowers the power of a control circuit portion and an air pressure operating portion, and has a control function by a microprocessor.

[0002]

2. Description of the Related Art Conventionally, there is an electro-pneumatic positioner for operating a diaphragm type control valve (hereinafter abbreviated as a control valve). FIG. 5 shows a block diagram of the electro / pneumatic positioner. In FIG. 5, 2 corresponds to the electric / pneumatic positioner, 3 corresponds to the control valve, 10 corresponds to the valve opening degree 3C of the control valve 3, and the electric / pneumatic positioner 2 receives the current signal 1B to set the SV (SV; Setpoint Value target value). ) Output controller. The electro-pneumatic positioner includes a torque motor 21, a balance beam 22, a pilot relay 23 controlled by a gap between a nozzle and a flapper, a feedback shaft 24, and a feedback lever 25.

From controller 10 to controller valve 3
The current signal 1B corresponding to the valve opening 3C of is the electro / pneumatic positioner 2
Is input to the torque motor 21 and the force is applied to the nozzle flapper across the balance beam 22 from the torque motor 21, and due to the gap between the nozzle and the flapper, the pilot relay 23
The operating air pressure 3B of is changed and the control valve 3 is driven. The valve opening 3C is transmitted from the valve shaft of the control valve 3 to the feedback lever 25 through the link mechanism, and the feedback lever 25 is displaced by the feedback shaft.
It is converted into force by 24 and is fed back to the balance beam 22. In this way, the current signal of the controller 10
A valve opening of 3C corresponding to 1B is set.

[0004]

In the conventional electro-pneumatic positioner, due to the size of the drive part of the control valve to be controlled and the friction of the gland packing for sealing the fluid, an offset is generated only by the proportional operation. When the gain is increased to reduce this offset, an oscillation phenomenon occurs. In particular, the difference between the response speed of the control valve in the opening direction and the closing direction, the tightening operation to improve the fluid sealing performance, and the resulting valve opening during reverse operation until opening The demand for precise control that reduces the amount of overshoot and responds at high speed to a large increase in frictional force and a large change in the valve opening setting within the normal valve opening range is: In the prior art, the stability of control must be emphasized, countermeasures must be taken by adding a throttle mechanism to the output air pressure of the positioner, and some of the required characteristics must be compromised.

The present invention has been made in view of the above points, and an object thereof is to solve the above-described problems and eliminate the influences of the size of the driving portion of the control valve to be controlled, the friction of the gland packing, etc. The present invention is to provide a valve positioner adapted to a digital transmission signal of control, which enables precise operation with high speed response with a small overshooting amount while enabling various operations.

[0006]

In order to achieve the above object, in the first aspect of the invention, a valve positioner for receiving a set value signal from a master controller and controlling the valve opening of a diaphragm type control valve is used. Is an interface unit that receives a set value signal from the master controller, and a microprocessor that calculates at least a control signal that performs a proportional-integral operation from the set value signal from the interface unit and the valve opening signal from the control valve. , A D / A converter for converting the control signal output from the microprocessor into an analog signal, an electric / air converter for receiving the analog signal from the D / A converter and converting the analog signal into an operation air pressure signal, and a control valve And a feedback lever that converts the valve opening signal of And an angle detector that feeds back a digital valve opening signal to the microprocessor by means of an angle signal. At least a control deviation of the difference between the set value signal from the master controller and the digital valve opening signal of the control valve. The control parameter for performing the proportional-plus-integral operation is changed according to the polarity.

Further, in the second aspect of the present invention, the microprocessor calculates a control signal for performing at least a proportional-plus-integral operation, and calculates a difference between the operation signal from the control deviation and the primary difference signal of the control deviation, It is assumed that the electric / air conversion unit is operated by the integrated value of the differential operation signal.
According to the third aspect of the invention, in the valve positioner that receives the set value signal from the master controller and controls the valve opening of the diaphragm type control valve, the valve positioner includes an interface section that receives the set value signal from the master controller. A microprocessor that calculates at least a control signal that performs a proportional-integral operation from a set value signal from the interface unit and a valve opening signal from the control valve, and D that converts the control signal output by this microprocessor into an analog signal. A / A converter, an electric / pneumatic converter that receives an analog signal from the D / A converter and converts it into an operation air pressure signal, a feedback lever that converts a valve opening signal from a control valve into an angle signal, and Digital signal to microprocessor by angle signal An angle detection unit for feeding back the valve opening signal, consisting, at least, of the control deviation and the control deviation by a difference between the digital valve opening signal setpoint signal and the control valve from the master controller 1
The control parameter is changed according to the polarity of the differential signal of the operation signal including the next differential signal.

In the fourth aspect of the invention, the valve opening of the control valve is fully closed or fully saturated,
When controlling from this saturation state to the normal operating range, the proportional band of the controller is a predetermined proportional band until the valve opening signal falls within the normal operating range of 0% to 100%. The deviation is controlled with a predetermined constant value according to the polarity of the control deviation at this time.

In the fifth invention, the control parameter changes the proportional gain.

[0010]

With the above arrangement, in the first aspect of the invention, the control parameter is changed according to the polarity of the control deviation which is the difference between the set value signal from the master controller and the digital valve opening signal of the control valve. It is possible to select a control parameter suitable for each response characteristic corresponding to the increasing / decreasing direction of the valve opening.

Further, in the second aspect of the invention, the difference between the operation signals is calculated from the control deviation and the primary difference signal of the control deviation, and the electric / air conversion section is operated by the integrated value of the difference operation signals. Therefore, by selecting the proportional gain and the integration time in accordance with the control valve characteristics, for a large setting change in the operating range, before the control deviation reverses, based on the rate of change of the valve opening, The operation signal is pulled back, and the overshooting amount can be reduced or the high-speed response control without the overshooting amount can be performed.

In the third aspect of the invention, the control parameter is changed in accordance with the polarity of the differential signal of the operation signal, so that the change of the valve opening degree can be dealt with, including a large setting change. It is possible to perform optimum control that matches the response characteristics. In the fourth aspect, the proportional band of the controller is a predetermined proportional band and the control deviation is the control deviation at this time until the operating air pressure signal enters the normal operating range of 0% to 100%. By controlling at a predetermined constant value according to the polarity of, the operating air pressure input to the control valve is at a predetermined value and escapes from the retightened area with large frictional force, and after that, normal By performing control with the control method described above, it is possible to perform smooth control with good controllability over a wide range as a control valve having a high fluid sealing property.

[0013]

1 is a block diagram of a valve positioner as one embodiment of the present invention, FIG. 2 is a detailed configuration diagram of one embodiment, FIG. 3 is a flow chart of a control calculation method in one embodiment, and FIG. The control response characteristic view from a fully closed state to a predetermined opening is shown, and the same reference numerals are given to the same functional members corresponding to FIG.

In FIG. 1, 1 is a master controller, 4 is a valve positioner as an embodiment, and 3 is a control valve to be controlled. Valve positioner 4
Is an interface unit 41 that receives the set value signal (SV) from the master controller 1, and a feedback signal PV that is proportional to the set value signal (SV) from this interface unit 41 and the valve opening signal 3C from the control valve 3. To control signal MV _k (MV: Manipulating Val)
ue), the microprocessor 42, the D / A converter 43 for converting the control signal MV _k output by the microprocessor 42 into an analog signal, and the analog signal from the D / A converter 43 to receive the operating air pressure. An electric / pneumatic pressure conversion unit 44 for converting into a signal 3B and a feedback lever 25 for converting a valve opening signal 3C from the control valve 3 into an angle signal 3D.
And an angle detection section for feeding back a digital feedback signal PV to the microprocessor 42 by the angle signal 3D, which in the illustrated example is composed of a potentiometer 46 and an A / D conversion section 47.

With such a configuration, a signal (SV set value) for setting the valve opening degree 3C of the control valve 3, for example, an optical digital signal is input from the master controller 1 to the valve positioner 4. The input SV setting value signal is converted into a digital electric signal by the optical signal interface 41 and input to the microprocessor 42. The microprocessor 42 converts the SV set value and an analog electric signal by the potentiometer 46 from the valve shaft of the control valve 3 via the feedback lever 25 by the link mechanism and a digital signal by the A / D converter 47. The feedback signal PV (PV; Pr;
esent Value, current value) and performs PI (D) calculation processing and outputs the control signal MV _k to the D / A converter 43. D / A
The conversion unit 43 converts the digital control signal MV _k from the microprocessor 42 into an analog voltage and applies it to the electric / pneumatic pressure conversion unit 44 to change the operating air pressure 3B, drive the control valve 3, and perform the negative feedback control loop. Make up. Therefore, the valve opening degree 3C of the control valve 3 corresponding to the SV set value signal of the master controller 1 can be determined.

FIG. 2 is a detailed block diagram of this embodiment. The control circuit section 4A, the electric / pneumatic pressure converting section 44, and the valve opening detecting section of the diaphragm control valve 3 (25, 46, 47) are roughly classified.
Composed of. In this embodiment, a 16-bit optical digital signal 1A is input to the control circuit 4A, and the valve opening degree detection section (25, 46, 47) of the control valve 3 is used to convert the valve opening degree 3C into an electric signal. It is a digital feedback signal PV to the microprocessor 42. Optical digital signal 1A
The integrated light receiving / emitting element 41A and the optical / electrical conversion unit (O / E conversion unit) 41C receive the optical digital signal 1A from the master controller 1 and convert it into the SV set value. Also, the valve opening
The digital feedback signal PV corresponding to 3C is converted into an optical digital signal 1A by the electric / optical conversion unit (E / O conversion unit) 41B and the integrated light emitting / receiving element 41A and transmitted to the master controller 1. Since the master controller 1 and the valve positioner 4 are connected by an optical digital transmission circuit, in addition to the SV setting value and PV value, the valve positioner 4
It is possible to communicate various kinds of maintenance information.

The SV set value of the optical digital signal 1A and the feedback signal PV are subjected to PI (D) control calculation by the microcomputer 42, converted into an electric signal by the D / A converter 43, and applied to the flapper 44A with a piezoelectric element. , Flapper with piezoelectric element 44A
By changing the gap between the nozzle 44B and the flapper 44A, the pressure of the air guided to the nozzle 44B (nozzle back pressure) is changed. The change in the nozzle back pressure is amplified by the pilot valve 44C to generate the operating air pressure 3B and drive the diaphragm control valve 3.

Next, the response speed difference in the increasing / decreasing direction of the control valve, including the difference in the friction coefficient due to the difference in the capacity of the operating portion of the control valve and the type of gland packing, etc., and the fluid sealing property when fully closed are improved. To increase the frictional force until the valve opening is about to open when operating in the opening direction.In addition, in the control within the normal valve opening range, a large change in the valve opening set value On the other hand, the demand for smooth and precise control with a small overshoot amount, high-speed response, and smooth control can be solved by the control method according to the flowchart shown in FIG.

In FIG. 3, in step S1, the control deviation e _k is calculated from the difference between the SV set value and the feedback signal PV.
The subscript _k here represents the k-th sample data operation. In step S2, the polarity of the control deviation e _k is checked. If the control deviation is positive, the procedure goes to step S11. If the control deviation is negative, the procedure goes to step S21. Hereinafter, unless otherwise specified, the control valve 3 is of a fully closed polarity in the direction in which the operating air pressure 3B is zero for the sake of simplification of description. Step S11
Check the SV setting value ≥ 0%. This means to check whether or not the set value SV from the master controller 1 has entered the normal operating region from the command state of the fully closing operation. SV ≧ 0%?
If Yes, the process moves to step S12. In step S12, the valve opening signal 3C swings to 0% or less means that the valve is in the fully closed position (in many cases, the tightening state), the control deviation e _k reverses to positive, and the control valve 3 is driven in the opening direction. When you do,
Tighten fully closed position (Yes) or control valve 3
It is to check whether is in the operating area (No).

Similarly, in step S21, the SV set value ≦ 100% is checked. This meaning is the set value from the master controller 1.
It is to check whether or not the SV has entered the normal operating range from the command state of the fully open operation. SV ≦ 100%? Yes with step S2
Move to 2. When the valve opening signal 3C is swung out to 100% or more in step S22, it means that the control valve 3 is in the fully open position, the control deviation e _k is negatively reversed, and the control valve 3 is driven in the closing direction. Is in the fully open position (Yes)
It is to check whether it is within the operating area (No). These steps S12 and S22 Yes form a control loop corresponding to a fourth invention described later. Further, step S12 and step S22 No mean that the control valve 3 is within the normal operating range and a normal control loop (step S33 or step S36). Further, Step S11 and Step S21 No are periods in which the SV set value and the feedback signal PV are both in the fully closed or fully open region and correspond to overshoot suppression control during transient phenomena, and this period is also the normal control loop. (Step S33 or Step S3
Means 6).

In the first aspect of the invention, a control parameter, for example, a proportional gain, is set according to the polarity of the control deviation e _k which is the difference between the set value signal (SV) from the master controller and the feedback signal (PV) of the control valve 1. change.
That is, when the control deviation e _k is positive, the proportional gain is set to P1 in step S33, and PI (D) is calculated based on the control deviation e _k in steps S34 and S35. When the control deviation e _k is negative, the proportional gain is set to P2 in step S36, and steps S34, S3
In step 5, PI (D) is calculated based on the control deviation e _k .

In the flow chart of FIG. 3, a so-called speed type calculation algorithm (calculation of the difference change in the valve opening signal) is shown as an example.

[0023]

[Equation 1]

In step S34, the differential operation output signal ΔMV _{k represented} by the equation (1) is calculated from the control deviation and the primary difference signal of this control deviation,

[0025]

[Equation 2]

This difference operation output signal ΔMV _k is calculated in step S3.
The operation output signal MV _k shown in equation (2) is calculated by integrating in step 5. This method corresponds to the second invention.
As the PI (D) calculation method, there is a so-called position calculation algorithm that directly calculates the valve opening signal MV _k itself, in addition to the velocity calculation algorithm described above. In any of the calculation algorithms, the difference in response speed depending on the increasing / decreasing direction of the control valve makes it possible to select the optimum control parameter according to the characteristics of the increasing / decreasing control valve, and stable control can be performed.

Next, a case will be described in which the SV set value greatly increases within the operating range, for example, 10% to 90%. When there is such a large change in the set value in the PI (D) control by the position type calculation algorithm, the operation output signal MV _k once becomes a positive saturated output, and this positive saturated output returns to the normal operating range. It almost started when the polarity of control deviation was reversed.
The delay of this control operation increases the amount of overshoot, and therefore PI (D) control by the position type operation algorithm usually requires a special additional function such as a reset windup prevention function. On the other hand
In the PI (D) control, the operation output signal MV _{k also} becomes a positive saturation output, but the point at which the positive saturation output begins to return to the normal operating range is a point well before the inversion time of the control deviation. Then, the polarity of the differential operation output signal ΔMV _k reverses with an increase in the rate of change of the PV signal and begins to return to the normal operating range. As a result, it is possible to perform control with a small overshoot amount or without overshoot amount. Therefore, instead of changing the control parameter according to the polarity of the control deviation in switching the control parameter according to the third aspect of the present invention, a differential operation output signal ΔMV consisting of the control deviation and the primary difference signal of this control deviation is used.
By changing the control parameter according to the polarity of _k ,
Good control can be performed even if the SV set value is changed significantly.

In the fourth aspect of the invention, the valve opening of the control valve is fully closed or fully saturated,
When the control valve is controlled from this saturation state to the normal operation range, the control valve is returned from full close or full open by excessive operation, and the friction coefficient is extremely increased until it enters the normal operation range. Therefore, until the valve opening of the control valve is returned from fully closed or fully opened and within the normal operating range of 0% to 100%, the proportional band of the controller is the predetermined proportional band and the control deviation is The control is performed at a predetermined constant value according to the polarity of the control deviation at that time. That is, steps S11 to S14 and steps S21 to S24 in FIG.
The loop of corresponds to this control. In step S11, the SV set value enters the operating range from fully closed, and when the control valve 3 is fully closed in step S12, step S13
Set the proportional gain to Ps (<P1, P2) with, add a constant constant es to the control deviation, and perform PI (D) calculation in steps S34 and S35. The operation output signal at this time is to put the control valve in the normal operating range by giving the control valve a force slightly larger than the force that can release it from the retightened state, and then, in step S12, set No loop. As described above, the control operation described above is performed in steps S33 to S35. Similarly, when the control valve 3 is fully opened and the condition for closing the control valve 3 is reached, the loop of steps S21 to S24 corresponds to this.

FIG. 4 is a control response characteristic diagram from the fully closed state of the control valve to a predetermined opening degree. FIG. 4A shows the control response characteristic according to the prior art, and FIG. 4B shows the present invention. 7 shows a control response characteristic according to an embodiment of the present invention. In FIG. 4, the horizontal axis represents the time axis from left to right, and the vertical axis represents the SV set value and valve opening signal. In the illustrated characteristic test data example, first, the SV set value is controlled to 50%, and then the lamp is operated in the closing direction at 50 → 0% / 15 seconds in a ramp shape, and is operated to -3%. The valve opening is SV
Follow-up control is performed with some time delay to the set value signal.
The valve opening itself is mechanically saturated at 0% and stops. SV
Since the set value signal is input up to -3%, the operating air pressure
3B is operated in the fully closed direction and becomes saturated.

In the characteristic test of FIG. 4, in order to make the effect of this tightening the same, the saturated and operated state is maintained for 10 minutes in the fully closed direction, and then the valve opening is changed to 10% stepwise. The response characteristic of the valve opening when it is made to show is shown. Note that FIG.
The same characteristic test hardware was used, and only the control method was tested by the conventional technique and the method according to the present invention. That is, as the hardware, the flapper 44A with a piezoelectric element shown in FIG. 2 was used. This was developed as a low power consumption configuration so that the valve positioner of the present invention can be operated by the battery unit 48 for a long period of time.
In the prior art of FIG. 4 (A), before the valve opening starts to move
It takes 15.5 seconds, and the settling time to respond to the SV set value signal is 25 to 30 seconds. On the other hand, in the control method based on the present invention of FIG. 4B, it takes 2 seconds before the valve opening degree starts to move.
It took about 3 seconds for the settling time to respond to the SV setting value signal, and the control response was significantly improved. In addition, in FIG. 4, after the step response characteristic test with the valve opening of 10%,
The figure shows the response characteristics when the SV setpoint signal change is changed in a ramp shape at a signal change rate of 100% / 30 sec. Here, since the signal change rate of the SV set value signal is slow, both the present invention and the prior art provide control without an excessive amount of jump.

According to the control method of the present invention, the amount of overshoot is small, a high-speed response is obtained, and smooth and precise control can be performed. In particular, the electric / pneumatic pressure conversion unit has a low power consumption configuration, and therefore, the hardware that causes a large control delay in exiting from the fully closed or fully opened state can also have its control characteristics remarkably improved by the control method of the present invention. .

[0032]

As described above, according to the present invention, by adopting the control calculation method adapted to the characteristics of the controller valve and switching the control parameters, the amount of overshoot is small, high speed response is made, and smooth and precise. Various controls can be enabled. In particular, the settling time for controlling the controller valve from fully closed or fully opened to the normal operating range can be shortened from a few fractions to about 1/10. The effect of significantly improving compatibility with

[Brief description of drawings]

FIG. 1 is a block diagram of a valve positioner as an embodiment of the present invention.

FIG. 2 is a detailed configuration diagram of an embodiment.

FIG. 3 is a flowchart of a control calculation method according to an embodiment.

4A and 4B are control response characteristic diagrams when the control valve is in a fully closed state to a predetermined opening degree. FIG. 4A is a control response characteristic diagram according to a conventional technique, and FIG. 4B is one example. Control response characteristic diagram

FIG. 5 is a block diagram of a prior art electro / pneumatic positioner.

[Explanation of symbols]

1 Master controller 10 Controller 1A Optical signal 1B Current signal 2 Electric / pneumatic positioner 21 Torque motor 22 Balance beam 23 Pilot relay 24 Feedback shaft 25 Feedback lever 3 Diaphragm type control valve 3A Supply pressure 3B Operating air pressure 3C Valve opening 3D Angle 3E Analog Signal 4 Valve positioner 4A Control circuit 41 Interface 41A Integrated light emitting / receiving element 41B E / O converter 41C O / E converter 42 Microprocessor 43 D / A converter 44 Electric / pneumatic converter 44A Flapper with piezoelectric element 44B Nozzle 44C pilot valve 46 potentiometer 47 A / D converter 48 cell unit SV set value signal PV feedback signal .DELTA.MV _k differential operation output signal MV _k operation output signal e _k control deviation P, P1, P2 proportional gain

Claims (5)

[Claims] 1. A valve positioner which receives a set value signal from a master controller and controls the valve opening of a diaphragm type control valve, wherein the valve positioner includes an interface section which receives the set value signal from the master controller, and the interface section. From the set value signal from the valve opening signal from the control valve, at least,
A microprocessor for calculating a control signal for performing a proportional-plus-integral operation, a D / A converter for converting the control signal output from the microprocessor into an analog signal, and an operation for receiving the analog signal from the D / A converter. An electric / pneumatic conversion unit for converting to a pneumatic signal, a feedback lever for converting the valve opening signal from the control valve into an angle signal, and a feedback of the digital signal valve opening signal to the microprocessor by the angle signal. And a control parameter for performing proportional-plus-integral operation according to the polarity of the control deviation that is at least the difference between the set value signal from the master controller and the digital valve opening signal of the control valve. A valve positioner characterized by changing the. 2. The valve positioner according to claim 1, wherein the control signal calculated by the microprocessor and performing at least the proportional-plus-integral operation is a difference between the control signal and a first-order difference signal of the control signal. A valve positioner which is operated, and operates the electric / pneumatic converter with the integrated value of the differential operation signal. 3. A valve positioner for receiving a set value signal from a master controller and controlling the valve opening of a diaphragm control valve, the valve positioner comprising an interface section for receiving the set value signal from the master controller, and the interface section. From the set value signal from the valve opening signal from the control valve, at least,
A microprocessor for calculating a control signal for performing a proportional-plus-integral operation, a D / A converter for converting the control signal output from the microprocessor into an analog signal, and an operation for receiving the analog signal from the D / A converter. An electric / pneumatic conversion unit for converting to a pneumatic signal, a feedback lever for converting the valve opening signal from the control valve into an angle signal, and a feedback of the digital signal valve opening signal to the microprocessor by the angle signal. An angle detection unit for controlling a control deviation, which is a difference between a set value signal from the master controller and the digital valve opening signal of the control valve, and a primary difference signal of the control deviation. The control parameter is changed according to the polarity of the differential signal of the operation signal Valve positioner. 4. The valve positioner according to any one of claims 1 to 3, wherein the valve opening of the control valve is in a fully closed or fully open saturated state, and a normal operating range is reached from this saturated state. When controlled, the proportional band of the controller is a predetermined proportional band until the valve opening signal falls within the normal operating range of 0% to 100%, and the control deviation is the control deviation of this time. A valve positioner characterized in that it is controlled by a predetermined constant value according to the polarity. 5. The valve positioner according to claim 1, wherein the control parameter changes a proportional gain.