JP2001050418A - Valve positioner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a wasteful time, and improve an oscillation and responsiveness characteristic by arranging an integral switch for turning on/off a function of an integrator in relation to change of a set signal on a front stage of a controller for taking in a signal of a valve opening sensor, and controlling a timing of an integral motion of the integrator. SOLUTION: An integral switch 30 is arranged on a front stage of an integrator 1a. A SP change detecting means 31 for detecting change of a set signal (a SP) and a PV value detecting means 32 are disposed, and the integral switch 30 is turned on/off on the basis of those signals. When the set signal SP is changed, its change is detected by the detecting means 31, a signal is outputted, and the integral switch 30 is turned off. Furthermore, calculation according to the SP is carried out, the PV is outputted from a positioning sensor 5 of a regulating valve. When the output of the PV is detected by the detecting means 32, a signal is outputted, the integral switch 30 is turned on, and an integral motion is started. In the case where a set signal is changed, the integrator is turned off, and the integrator is operated in the case where the set signal is not changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a valve positioner for controlling a valve opening of a control valve having a pneumatic drive unit to a value corresponding to a signal, and to a method for calculating a control signal for calculating a control signal. is there.

[0002]

2. Description of the Related Art An algorithm for controlling a control valve is one of the important factors that determine the performance of a product. Conventionally, many valve positioners are mechanical, and the control algorithm is determined by the mechanical mechanism, so overwhelmingly P (proportional)
There were many controls. (Conversely, algorithms other than P control
It was difficult with a mechanical mechanism).

However, in recent years, an electronic valve positioner has been developed, and further, an arithmetic function such as a CPU has been mounted on the valve positioner. With this function, control algorithms can be realized by software, and control calculations of almost all types have been made possible.

The control algorithm is based on P (proportional) control,
It has evolved into PID (proportional, integral, derivative) control. As a result, the controllability of the control valve has been significantly improved. However, with the development of technological innovation, market requirements have become more severe, and at present, a valve positioner with even better controllability has been demanded.

[0005] Against this background, development of control valve control algorithms has been actively pursued. The adopted algorithm is generally a PID control algorithm, but the PID algorithm alone cannot sufficiently absorb the nonlinearity of the control valve.
Therefore, the controllability of the control valve is being improved by adding various functions to the PID algorithm.

FIG. 10 is a block diagram showing an example of control of a conventional valve positioner. In the figure, an input signal SP and an output signal PV from a position sensor 5 are input to a controller 1 including an integrator 1a, a proportional unit 1b, and a differentiator 1c, and a control signal MV is output from the controller 1.

This signal MV is converted to a signal converter (I / P Conv
erter) 2 to be converted to an air signal and the pilot relay 3
The pressure is input to the control valve 4 to displace the valve stem. The displacement of the stem is detected by the position sensor 5,
It is input to the controller 1 as a feedback signal.

In the above-mentioned conventional valve positioner, the most general operation algorithm of digital PID control is as follows. P (n) = Sp (n) -Pv (n) I (n) = Δt / Ti * P (n) + I (n-1) D (n) = Td / (Δt + 1 / γ * Td) * (P (n-1) -P (n) + 1 / γ * D (n-1)) MV (n) = Kp * (P (n) + I (n) + D (n))

Sp (n): target value Pv (n): feedback value (signal of valve opening) P (n): proportional unit I (n): integrator D (n): differentiator MV (n) : Control signal Δt: Control cycle Ti: Integration time Td: Differential time γ: Differential gain Kp: Proportional gain

Next, the operation of this algorithm will be described. The algorithm, literally PID, is a proportional
(P), an integrator (I), and a differentiator (D). The control signal MV is obtained by multiplying a value obtained by adding the values of P, I, and D by a proportional gain KP.

The proportionality device P detects an input signal SP of the positioner and a stem displacement indicating a valve opening degree of a control valve (not shown) by the position sensor 5, and converts an electric signal of the sensor into an A / A signal.
The difference (also called deviation) from the PV value converted into a digital value by the D converter is output.

The integrator 1a integrates the deviation at a rate determined by a parameter set by the integration time Ti.
The differentiator differentiates the deviation at a rate determined by a parameter set by a differentiation time and a differentiation gain. The final control signal MV is a proportional unit 1b, an integrator 1a, a differentiator 1c
Is multiplied by the proportional gain KP to the value obtained by adding the values of

The controller 1 performs such a calculation to determine the MV value in order to make the SP track the PV quickly and accurately. For example, when there is a difference between SP and PV, the controller 1 changes the MV value in a direction in which the PV and SP are brought closer. When there is no difference between SP and PV, the MV value does not change.

Although this algorithm is simple, it is essentially excellent, but if the controlled object has nonlinearity, the controllability may be significantly deteriorated. (The control target for the controller 1 refers to the range from the I / P converter 2 for giving the MV value to the control valves 4... Valves.)

Next, the specific non-linearity of the controlled object will be described. The typical non-linearity of the controlled object is shown in FIG.
1, the hysteresis includes the hysteresis of each element such as the control valve 4 and the pilot relay 3.

The effect of these hysteresis on PID control will be described. The pilot relay hysteresis is
If there is no change in the nozzle back pressure that has a hysteresis with respect to the change in the nozzle back pressure output from the I / P converter (electro-pneumatic conversion mechanism) 2 and there is no change in the nozzle back pressure that breaks the hysteresis, the pilot relay 3 operates the air actuator of the control valve 4. It has the property that the air flow rate cannot be changed.

The hysteresis of the control valve 4 has such a property that the stem of the control valve 4 cannot be driven until the air pressure of the pneumatic actuator breaks the hysteresis. The hysteresis described above is a typical example, but the hysteresis dealt with in the present invention is the controller 1 of the positioner.
The control amount (MV value) calculated by is calculated by the valve opening signal of the control valve 4.
The feedback signal (PV value) includes all hysteresis before returning.

[0018]

When such a hysteresis exists in the control object, for example, if a setting signal is given to a positioner, the PV value will not change unless the control signal (MV value) overcomes the hysteresis. It does not change.

In addition, the positioner has a delay when the I / P converter 2 converts an electric signal into an air signal with respect to a change in the MV value. Furthermore, it amplifies the flow rate of the air signal,
When supplying the air to the control valve 4, a time constant delay occurs in accordance with the capacity of the air actuator of the control valve 4.

Due to the hysteresis and the delay time, even if the setting signal is given, the PV value cannot respond immediately, and a dead time occurs. The greater the hysteresis, the longer the dead time.

Conventional integrator 1a accumulates this deviation in accordance with the integration time. Eventually, the PV value changes, and the deviation decreases.
It does not settle at the value indicated by SP, and overshoot occurs.

Once overshoot occurs, the controller 1
Performs a control operation to restore it, but also in this case, hysteresis occurs and it takes a long time to return.
Further, if the system has a large hysteresis and a long delay time, in the worst case, when the overshoot is returned, the overshoot occurs in the opposite direction, and the oscillation may be repeated.

FIG. 12 shows the change of the PV value including the dead time after the input of the set value SP and the state of the integration of the integrator. The only way to solve this phenomenon with the conventional PID is to reduce the proportional gain extremely and set the integration time extremely long. This adjustment significantly deteriorates the response characteristics of the control valve 4.

The present invention has been made to solve such a problem. By controlling the timing of the integration operation of the integrator 1b, the present invention realizes a valve positioner with improved oscillation and response characteristics. With the goal.

[0025]

In order to achieve the above object, according to the present invention, in the first aspect, a signal of a valve opening sensor is fetched and set using at least a controller equipped with an integrator. In a valve positioner for controlling the valve opening to a value corresponding to a signal, an integration switch for turning on and off a function of the integrator in relation to a change in the setting signal is provided.

According to a second aspect of the present invention, in the valve positioner according to the first aspect, a set signal change detecting means for detecting a change in the set signal, and a position for detecting a position signal of the valve opening degree sensor which changes according to the change in the set signal. Signal change detecting means, and an integrating switch for turning on and off the function of the integrator based on the output of the detecting means.

According to a third aspect of the present invention, in the valve positioner of the second aspect, when the setting signal change detecting means detects a change in the setting signal, the function of the integrator is turned off, and the position signal change detecting means changes the valve opening. The function of the integrator is turned on when a change in the position signal of the sensor is detected.

According to a fourth aspect of the present invention, there is provided the valve positioner according to the first aspect, further comprising a deviation detecting means for detecting a deviation between the setting signal and the position signal of the valve opening degree sensor, the deviation relating to the deviation detected by the deviation detecting means. And the function of the integrator is turned on and off.

According to a fifth aspect of the present invention, in the valve positioner according to the fourth aspect, the deviation detecting means has a function of determining a predetermined range of small, medium, and large deviations in three stages. . In claim 6, claim 5
The described valve positioner is characterized in that the integration function is turned off when the deviation is small, turned on when the deviation is medium, and turned off when the deviation is large.

According to a seventh aspect of the present invention, in the valve positioner according to the first aspect, a position signal change detecting means for detecting a position signal of a valve opening degree sensor which changes according to a change in a set signal; An integration timer that functions in connection with the output is provided, and the integration function is turned on and off in accordance with the set time of the integration timer.

According to an eighth aspect of the present invention, in the valve positioner according to the seventh aspect, a foot {fore} arithmetic function for performing operating point compensation on a set value is provided.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 shows a schematic configuration of an embodiment according to claim 1 of the present invention. In the conventional example described with reference to FIG. 10, an integration switch 30 is provided in a stage preceding an integrator 1a, and a trigger for making the integration switch 30 function is provided. SP change detecting means 31 for detecting a change in SP (setting signal) and PV value detecting means 3
2 in that the integration switch 30 is turned on and off based on these signals. In FIG. 1, the signal converter (I / P Converter) 2, the pilot relay 3, and the control valve 4 are collectively referred to as a drive unit 20.

In the configuration shown in FIG. 1, when the setting signal SP changes, the SP change detecting means 31 detects the change and outputs a signal to turn off the integrating switch 30. Next, a calculation according to SP is performed, and the stem position of the control valve is displaced to output PV from the position sensor 5. When the PV value detection means 32 detects this, a signal is output and the integration switch 30 is turned on. Start the integration operation.

FIG. 2 is a flowchart of the valve positioner having the structure shown in FIG. When detecting that the setting signal has changed, the controller 1 proceeds in the Y direction to set a flag, and then, when detecting that the PV value has changed, proceeds to the Y direction to reset the plug for operating the integrator. P
As long as the V value does not change, the process proceeds in the N direction and the integrator is kept off (stopped).

If the setting signal does not change, it is checked whether the flag is set. If not, N is set.
Reset the flag that goes in the direction and activates the integrator.
If the flag is set, the flow advances in the Y direction after the change of the PV value, and the flag for operating the integrator is reset.

FIG. 3 shows the change in SP and PV and the integration operation of the integrator according to the above configuration. It can be seen that the overshoot of PV is improved by turning off the integration operation of the integrator in the dead time. Understand.

FIG. 4 shows an example of the second embodiment. This example is different from the conventional example described with reference to FIG. 10 in that an integrating switch 30 is provided in a stage preceding the integrator 1a, and a deviation detecting means 33 is provided in a stage preceding the controller 10 as a trigger for operating the integrating switch 30. Is different in that the integration switch 30 is turned on and off based on the signal. In FIG. 4, the signal converter (I / P Converter) 2, the pilot relay 3, and the control valve 4 are collectively referred to as a drive unit 20.

In FIG. 4, if the deviation | SP-PV | is a first predetermined range (for example, within 1%... A) as shown in FIG.
0 is turned off, and | SP-PV | exceeds the first predetermined range and falls within the second predetermined range (for example, 1% or more → 10
%)... B), the integration switch 30 is turned on, and | SP−PV | is set to a second predetermined range (for example, 1%).
0% or more... C), the integration switch 30 is turned off.

According to the configuration of FIG. 4, the integration function is stopped while the deviation is extremely small (within 1%), and the deviation is moderate (1 to 10).
% Range), the integration function is provided, and the deviation is large (10%).
%), The integration function is stopped. As described above, when a deviation exceeding a certain value occurs, the integration operation of the integrator 1a is stopped and the influence of the dead time is reduced from the integrator 1a, so that control according to the deviation can be performed.

FIG. 6 is a block diagram showing an example of the third embodiment. In FIG. 6, an integration switch 30 is provided at a stage preceding the integrator as compared with the conventional example described with reference to FIG.
The difference is that a P change detecting means 31 and an integration timer 34 operated by the output of the detecting means are provided.

In the figure, a feedforward computing unit (hereinafter simply referred to as FF computing unit) 35 is provided.
The function of the FF calculator 35 will be described later. 6, the signal converter (I / P Converter) 2, the pilot relay 3, and the control valve 4 are collectively referred to as a drive unit 20.

FIG. 7 shows a flowchart of the valve positioner shown in FIG. In FIG. 7, the setting signal SP
Is changed in the Y direction, the integration timer 34 is set, and the integrator 1 is set until the timer 34 times out.
The operation of a is stopped. If not, the process proceeds in the N direction and determines whether the integration timer has timed out. If the timeout has occurred, the integrator 1a
Is operated, and if not, the operation proceeds in the N direction and the integrator 1
The operation of a is stopped.

As described above, when the set value (SP) has changed, the timer 34 is set. When the timer is operating, the integration is stopped, and when the timer times out, the integration is restarted. That is, when the operation time of the integration timer 34 is longer than the dead time caused by the hysteresis and the delay time, there is no extra integration amount accumulated by the integrator in the dead time.

In this case, the time of the timer 34 may be longer than the dead time, but it is very difficult to predict the state of the hysteresis, so the timer is set to be longer. Then, the operating point correction caused by the change of the target value, which is the original function of the integration, takes the integration stop time and may cause a steady-state deviation.

In this case, the timer times out,
When the integrator 1a starts operating, this steady-state deviation is
Can be absorbed and removed, but has the disadvantage of longer settling time. Therefore, the operating point correction on the forward side can be compensated by feed forward because the gain on the forward side is known in advance, and by adding feed forward according to SP, even if the integration timer is set longer, the steady-state deviation can be reduced. Can be controlled.

The calculation of the MV value in this case is as follows: MV = Kp * (P + I + D) + FF (feet {forearm}). Here, the state in which the integration timer 34 operates and the integrator 1b is stopped is assumed to be P control, and for simplicity of description, a control system block shown in FIG. 8 will be considered. In FIG. 8, in the case of a control system in which an input is given by SP, a proportional control is performed, an operation amount U is output, and a disturbance W is given, a step response can be obtained without considering noise or the like.
It is assumed that the system is a stable control system in which the control amount and the operation amount finally settle to a constant value. The steady-state deviation at this time can be expressed by the following equation.

Err (steady deviation) = SP-PV PV = G × (U + W) U = Kp × Err Therefore, Err = {1 / (1 + G × Kp)} × SP- {G / (1 + G × Kp)} × W ... 1 According to Equation 1, it can be seen that in the case of the P control, a steady-state error proportional to SP remains. This steady-state error is made up of a steady-state error due to the input SP shown in the first term of Equation 1 and a steady-state error due to the disturbance W shown in the second term.

Therefore, in order to remove such a steady deviation, the integrator 1b is required. However, when the integration timer 34 is used, the integrator 1b does not operate until the timer times out, so that a set of steady-state errors remains, and after the timer 34 times out, the integrator 1b absorbs the steady-state errors. . In this case, depending on the setting of the time of the integration timer 34, very good response characteristics cannot be expected.

Here, since G, Kp, and Sp are known, the steady-state deviation of the first term of Equation 1 can be predicted by feedforward. In the second term, it is difficult to predict the magnitude of the disturbance W, and thus it is difficult to incorporate the second term into feedforward. Therefore, the characteristics while the integrator 1b is stopped can be improved by setting the feedforward FF by the following equation and configuring a control system as shown in FIG.

FF = SP / G... 2 The steady-state error Err in this block is Err = − {G × W / (1 + G × Kp)}...

By introducing the FF, the steady-state deviation can be reduced even if the integrator 1b is stopped by the integration timer. Further, as for the disturbance W, a disturbance such as a temperature characteristic of the I / P converter 2 and the pilot relay 3 shown by the drive unit 20 in FIG. 6 may be considered. It has a sufficiently large time constant, and the disturbance of Expression 3 can be absorbed by the ordinary integrator 1b.

It is to be noted that the above description of the present invention has been presented by way of illustration and example only, and of particular preferred embodiments. Thus, it will be apparent to one skilled in the art that the present invention may be modified or modified in many ways without departing from its essentials. The scope of the present invention, which is defined by the description in the appended claims, is intended to cover alterations and modifications within the scope.

[0053]

As described above, according to the present invention, the signal of the valve opening sensor is fetched and the valve opening is adjusted to a value corresponding to the set signal using at least a controller equipped with an integrator. In the valve positioner to be controlled, an integration switch for turning on and off the function of the integrator in relation to the change of the setting signal is provided, so that the oscillation and response characteristics are improved by controlling the timing of the integration operation of the integrator. A valve positioner was realized.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an example of an embodiment of a valve positioner according to the present invention.

FIG. 2 is a flowchart of the valve positioner shown in FIG.

FIG. 3 shows a PV including a dead time after a set value SP is input.
FIG. 6 is a diagram illustrating a change in a value and a state of integration by an integrator.

FIG. 4 is a schematic configuration diagram showing another example of the valve positioner according to the present invention.

5 is a diagram showing the relationship between the deviation of the valve positioner having the configuration shown in FIG. 4 and the on / off of the integrator.

FIG. 6 is a schematic configuration diagram showing another example of the valve positioner according to the present invention.

FIG. 7 is a flowchart of the valve positioner shown in FIG. 6;

FIG. 8 is a hypothetical diagram of a control system when a disturbance is given to the valve positioner shown in FIG. 8;

FIG. 9 is a diagram illustrating an example of improvement of characteristics while the integrator is stopped by forming a feed forward.

FIG. 10 is a configuration diagram showing a conventional valve positioner.

FIG. 11 is a diagram showing hysteresis generated in a valve positioner.

FIG. 12 is a diagram showing a relationship between a set value (SP) and an operation amount (PV).

[Explanation of symbols]

 1, 10 Controller 1a Integrator 1b Proportional unit 1c Differentiator 2 I / P converter 3 Pilot relay 4 Control valve 5 Position (position) sensor 20 Drive unit 30 Integration switch 31 SP change detecting means 32 PV change detecting means 33 Deviation detecting means 34 integration timer 35 feedforward computing unit

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 3H062 AA15 BB10 FF01 FF41 3H106 DA05 EE04 EE48 FB07 FB27 GC29 KK31 5H004 GA03 GA04 GA11 GB01 HA07 HB07 JB19 KA69 KB02 KB04 KB06 KB13 KB32 KC39 KC53 LA01 LA03 LA07 MA05 MA05 FF01 KK32 KK37

Claims (8)

[Claims] 1. A valve positioner which receives a signal from a valve opening sensor and controls the valve opening to a value corresponding to the setting signal by using at least a controller equipped with an integrator. A valve positioner provided with an integration switch for turning on and off the function of the integrator. 2. A method according to claim 1, further comprising: setting signal change detecting means for detecting a change in the setting signal; and position signal change detecting means for detecting a position signal of the valve opening sensor which changes according to the change in the setting signal. 2. The valve positioner according to claim 1, further comprising an integration switch for turning on and off the function of the integrator based on the output of the valve. 3. The integrator function is turned off when the setting signal change detecting means detects a change in the setting signal, and the integrator is turned off when the position signal change detecting means detects a change in the position signal of the valve opening sensor. 3. The valve positioner according to claim 2, wherein the function is turned on. And a deviation detecting means for detecting a deviation between the setting signal and the position signal of the valve opening sensor, wherein the function of the integrator is turned on / off in relation to the deviation detected by the deviation detecting means. The valve positioner according to claim 1, wherein: 5. A valve positioner according to claim 4, wherein said deviation detecting means has a function of judging a predetermined range of small, medium and large deviations in three stages. 6. The valve positioner according to claim 5, wherein the integration function is turned off when the deviation is small, turned on when the deviation is medium, and turned off when the deviation is large. 7. A position signal change detecting means for detecting a position signal of a valve opening sensor which changes according to a change of a setting signal, and an integration timer functioning in relation to an output from the position signal change detecting means. 2. The valve positioner according to claim 1, wherein the integration function is turned on / off according to a set time of the integration timer. 8. A method for performing operating point compensation on a set value.
8. The valve positioner according to claim 7, further comprising a foot {fourth} calculation function.