JP3057635B2 - Valve positioner - Google Patents

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 the control valve by air pressure so that the valve opening of the control valve coincides with a target valve opening. The present invention relates to a valve positioner capable of shortening a response time of a valve.

[0002]

2. Description of the Related Art A conventional valve positioner controls an air pressure as an operation amount so that a valve opening signal from a valve opening detector attached to a control valve matches a target valve opening signal. , Its control algorithm is PID (Prop
(ortional, Integration and Differential) control.

FIG. 6 is a block diagram showing an example of such a conventional valve positioner. In FIG. 6, 1 is a subtractor, 2 is a control circuit, 3 is a D / A converter, 4 is a torque motor, 5 is a pilot relay, 6 is a control valve, 7 is a valve opening detector, and 8 is A / D conversion. , 100 is a target valve opening signal, and 101 is a valve opening signal.

[0004] Also, 1 to 3 and 8 denote control means 50 and 4.
And 5 constitute the operation means 51, and 7 constitute the detection means 52, respectively.

[0005] The target valve opening signal 100 is input to the addition input terminal of the subtractor 1, and the output of the subtracter 1 is connected to the control circuit 2. The control signal from the control circuit 2 is connected to the D / A converter 3, and the output of the D / A converter 3 is connected to the torque motor 4.

An air pressure signal from the torque motor 4 is input to a pilot relay 5, and an air pressure signal from the pilot relay 5 is supplied to a control valve 6.

On the other hand, the valve opening detector 7 is attached to the control valve 6, the output of the valve opening detector 7 is connected to the A / D converter 8, and the output of the A / D converter 8 is the valve opening. It is connected to the subtraction input terminal of the subtractor 1 as the degree signal 101.

Here, the operation of the conventional example shown in FIG. 6 will be described. The valve opening of the control valve 6 is detected by a valve opening detector 7 and is input to the subtractor 1 via an A / D converter 8 so that a deviation from a target valve opening signal 100 from an upper controller or the like is calculated. The operation is performed by the subtractor 1.

Based on this deviation, the control circuit 2 supplies an operation amount of the torque motor 4, which is a control signal, to the torque motor 4 via the D / A converter 3.

The torque motor 4 generates an air pressure signal based on the control signal, and supplies the air pressure signal to the pilot relay 5. The pilot relay 5 amplifies this pneumatic signal appropriately and supplies it to the diaphragm actuator of the control valve 6.

The diaphragm actuator converts a pneumatic signal into a force to change the opening of the control valve 6.

The valve opening thus changed is detected by the valve opening detector 7 and fed back to the control circuit 2 to be used for further control of the valve opening.

That is, by repeating such control, the control circuit 2 reduces the deviation supplied from the subtracter 1 to "0".
Thus, the operation amount of the torque motor 4 is controlled so that the valve opening of the control valve 6 finally matches the target valve opening signal 100 input from a higher-order controller or the like.

Further, a PID operation expression of the PID control will be described with reference to FIG. Fig. 7 shows P of the valve positioner.
FIG. 7 is a block diagram for explaining ID control. In FIG. 7, 1, 50, 100, and 101 have the same reference numerals as in FIG. 6, 9 is an integrator, 10 is a proportional unit, 11 is a differentiator, 12
Is an amplifier. Reference numeral 13 denotes an operation amount, and reference numeral 14 denotes a limiter of the operation amount.

However, the integrator 9, the proportional unit 10, and the differentiator 1
Although the functions such as 1 are actually realized as software in the control circuit 2, the above functions will be described as circuits such as an integrator for the sake of simplicity.

In FIG. 7, the target valve opening signal 100 is set to "s".
p ”, the valve opening signal 101 is“ pv ”, and the calculation cycle is“ Δ ”.
t ”, the differential gain and the differential time of the differentiator 11 are set to“ 1 / γ ”
And "Td", the integration time of the integrator 9 is "Ti", and the gain of the amplifier 12 is "Kp".

At this time, the deviation "err" between the target valve opening signal 100 and the valve opening signal 101 is err (m) = sp (m) -pv (m) (1). Here, "m" indicates a signal or the like measured at present, and for example, "m-1" indicates a signal or the like measured last time.

Similarly, the output "I" of the integrator 9 and the proportional unit 1
The output “P” of 0 and the output “D” of the differentiator 11 are I (m) = I (m−1) + Δt / Ti × err (m) (2) P (m) = err (m) ( 3) D (m) = Td / (Δt + γ · Td) × (err (m) −err (m−1) + γ · D (m−1)) (4)

The manipulated variable "u" is given by u (m) = Kp × (P (m) + I (m) + D (m)) (5)

When the valve opening of the control valve 6 does not change due to closing or closing (hereinafter referred to as saturation), the deviation does not become "0" but always remains at a constant value.

If the operation of the integrator 9 is continued in this state, the output of the integrator 9 will increase or decrease indefinitely. Therefore, it is necessary to limit the operation of the integrator 9 by determining a saturation condition in advance.

For example, when the upper limit value and the lower limit value of the saturation condition of the operation amount are “satH” and “satL”, respectively, the operation amount limiter 14 sets u (m) ≧ satH or u (m) ≦ satL ( 6) When the following condition is satisfied, the switch indicated by “A” in FIG. 7 is set to “off” to stop the input of the deviation to the integrator 9.

At this time, the output of the integrator 9 maintains the value integrated last time, that is, I (m) = I (m-1) (7)

[0024]

However, in the valve positioner, from the viewpoint of emphasizing the closing of the control valve 6, the valve is not closed when the target valve opening signal 100 is "0% (closed state)". With the target valve opening signal 100 of 2 to 3%, the control valve 6 is closed.

Under the above set conditions, if the target valve opening signal 100 is "0%", the control valve 6 is closed before the deviation becomes "0". The integrator 9 continues to integrate the deviation until the saturation condition as shown is satisfied.

FIGS. 8A and 8B are timing charts for explaining such a state. FIG. 8A shows the operation state of the control valve 6, FIG. 8B shows the target valve opening signal 100, and FIG. 8C shows the output signal of the integrator 9. Are respectively shown.

When the target valve opening signal 100 is "0%",
Even if the control valve 6 is saturated and the operation of the control valve 6 is stopped at the point indicated by “A” in FIG. 8, the integration is performed until the output signal of the integrator 9 decreases to the saturation point indicated by “B” in FIG. The vessel 9 continues to operate.

Next, even if the target valve opening signal 100 is switched to "5%" at the point indicated by "c" in FIG. 8, "d" in FIG.
The operation of the control valve 6 does not start until the output signal of the integrator 9 increases to the operating point shown in FIG.

That is, once the integrator 9 is saturated, even if the target valve opening signal 100 is changed, the control valve 6 does not respond for the time indicated by "e" in FIG. there were. Accordingly, an object of the present invention is to provide a valve positioner capable of shortening a response time of a control valve to a change in a target valve opening signal even when an integrator is saturated.

According to a first aspect of the present invention, there is provided a valve positioner for controlling the control valve by air pressure so that the valve opening of the control valve coincides with a target valve opening. said detection means for detecting the valve opening of the valve, and operating means for operating the valve opening of said regulating valve and controls the operation means so that the output and the target valve opening degree of the detecting means matches The output of the detection means is constant
The output of the detection means and the target valve
A state in which the deviation from the opening exceeds a certain level for a certain period of time
If it continues, it is determined that the control valve is saturated and
Reduce the output time of the detection means
When the deviation falls below a certain value, the control valve becomes saturated.
Control means for determining that the sum state has been released and returning the integration time to the original value .

In order to achieve such a task, the present invention
In a second aspect of the invention, in a valve positioner that controls the control valve by air pressure so that the valve opening of the control valve matches the target valve opening, detection means for detecting the valve opening of the control valve; Operating means for operating the valve opening degree, and controlling the operating means so that the output of the detecting means coincides with the target valve opening degree, and stops the integration operation when the control valve becomes saturated. And control means.

In order to achieve such a task, the present invention
According to the third aspect of the present invention, in the second aspect of the present invention, a state in which the output of the detecting means does not change at a certain fixed width and the deviation between the output of the detecting means and the target valve opening is present for a certain degree or more. If the control valve is determined to be saturated when continued for a certain period of time, the output signal of the detection means changes, or,
When the deviation has become equal to or less than a predetermined value, or when the value of the target valve opening is changed, it is determined that the saturation state of the control valve has been released.

[0033]

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a circuit diagram showing one embodiment of a valve positioner according to the present invention.

In FIG. 1, 1,3 to 8,51,52,1
Reference numerals 00 and 101 denote the same reference numerals as in FIG. 6, reference numeral 2a denotes a control circuit, and reference numerals 1, 2, 3 and 8 denote control means 50a. The basic connection relationship is the same as that in FIG.

Here, the difference between the conventional example shown in FIG. 6 and the present embodiment is a difference in the control method of the integrator 9 when the control valve 6 is saturated. The process for reducing the integration time will be described with reference to FIGS.

FIG. 2 is a flowchart for explaining the operation of the control circuit 2a, and FIG. 3 is a timing chart for explaining the operation corresponding to the flowchart.

At this time, if the output signal of the valve opening degree detector 7 does not change with a certain fixed width and the state where the deviation exists for a certain amount or more continues for a certain period of time, the control valve 6 is saturated. Judge.

If the output signal of the valve opening detector 7 changes or the deviation becomes smaller than a certain value, it is determined that the saturation state of the control valve 6 has been released.

If the control valve 6 is saturated, the integration time "Ti" is reduced, and if the saturation is released, the integration time "Ti" is returned to the original value.

As shown in FIG. 2A, the valve opening signal 101
Is determined to be smaller than a predetermined value “α”. If the difference between the valve opening signals 101 is equal to or larger than “α”, it is determined that the saturation state of the control valve 6 has been released, and FIG. The counter is reset by setting "i = 0" as shown in FIG.
As shown in (c), the integration time “Ti” is changed to the original integration time “
Return to T1 ".

Then, the PID calculation is performed as shown in FIG. 2D, and the current valve opening signal 101 is held for the next processing as shown in FIG. 2E.

In FIG. 2A, if the difference between the valve opening signals 101 is smaller than "α", it is determined whether the deviation is larger than a constant value "β" as shown in FIG. 2F.

If the deviation is equal to or less than "β", it is determined that the saturation state of the control valve 6 has been released, and the control valve 6 shown in FIG.
The processing of (b) to (e) is performed.

On the other hand, if the deviation is larger than “β”, FIG.
As shown in (g), the counter is counted up as "i = i + 1".

Further, as shown in FIG. 2H, “i> δ
(Δ is a constant value) ", it is determined that the states of FIGS. 2 (a) and 2 (f) have passed for a predetermined time or more, that is, it is determined that the control valve 6 has become saturated, and FIG. ), The integration time “Ti” is set to a shortened integration time “T2”.

Conversely, if “i ≦ δ” in FIG. 2H, the processing of FIGS. 2C to 2E is performed.

In FIG. 3, (a) shows the operating state of the control valve 6, (b) shows the target valve opening signal 100, and (c) shows the output signal of the integrator 9.

In FIG. 3, "A" indicates an output signal of the integrator 9 according to the algorithm of FIG. 2, and "B" in FIG. 3 indicates an integration when the integration time is constant irrespective of whether the control valve 6 is saturated. It is an output signal of the device 9.

At the time of "c" in FIG. 3, (a) in FIG.
When the conditions (f) and (h) are satisfied, the integration time becomes “T
2 ", the output of the integrator 9 sharply falls as shown at" d "in FIG. 3 and decreases to the saturation point of the integrator 9 shown at" e "in FIG.

Even if the target valve opening signal 100 is switched at the time indicated by "f" in FIG. 3, the output signal of the integrator 9 becomes the operating point indicated by "g" in FIG. Up to the point "H" in FIG.

In FIG. 3, the control valve 6 operates at the point "h" to release the saturation state of the control valve 6, so that the integration time returns to the original value "T1", and the output signal of the integrator 9 becomes gentle. To rise.

Accordingly, the time from the time when the target valve opening signal 100 is changed to the time when the control valve 6 starts responding is “R” in FIG.
It can be seen that the integration time indicated by “nu” in FIG. 3 is shorter than the time required to start the response when the response is constant.

As a result, when the control valve 6 is saturated, the integration time of the integrator 9 is shortened to change the target valve opening signal 100 and the time until the control valve 6 starts responding. Can be shortened.

Second, a process for stopping the operation of the integrator 9 when the control valve 6 is saturated will be described with reference to FIGS.

FIG. 4 is a flowchart for explaining the operation of the control circuit 2a, and FIG. 5 is a timing chart for explaining the operation corresponding to the flowchart.

At this time, when the output signal of the valve opening degree detector 7 does not change with a certain fixed width and the state where the deviation exists for a certain amount or more continues for a certain period of time, the control valve 6 is saturated. Judge.

When the output signal of the valve opening detector 7 changes, or when the deviation becomes smaller than a certain value, or when the value of the target valve opening signal 100 changes, the control valve 6 changes. It is determined that the saturation state has been released.

When the control valve 6 is saturated, the operation of the integrator 9 is stopped, and the output signal immediately before the stop is held.
When the saturated state is released, the operation of the integrator 9 is started.

As shown in FIG. 4A, the valve opening signal 101
Is determined to be smaller than a predetermined value "α", and if the difference between the valve opening signals 101 is equal to or larger than "α", it is determined that the saturation state of the control valve 6 has been released, and FIG. As shown in FIG. 4, the counter is reset by setting "i = 0", and FIG.
The integrator 9 is operated or the operation is maintained as shown in FIG.

Then, the PID calculation is performed as shown in FIG. 4D, and the current target valve opening signal 100, the valve opening signal 101 and the output signal of the integrator 6 are obtained as shown in FIG. Is held for the next processing.

In FIG. 4A, if the difference between the valve opening signals 101 is smaller than "α", it is determined whether the deviation is larger than a constant value "β" as shown in FIG. to decide.

If the deviation is equal to or smaller than "β", it is determined that the saturation state of the control valve 6 has been released, and the same as in FIG.
The processing of (b) to (e) is performed.

On the other hand, if the deviation is larger than “β”, FIG.
As shown in (g), the counter is counted up as "i = i + 1".

As shown in FIG. 4H, "i>δ"
If it is, it is determined that the states of FIGS. 4A and 4F have passed a predetermined time or more, and if “i ≦ δ”, it is determined that the state of FIG.
The processing of (c) to (e) is performed.

Further, it is determined whether or not the target valve opening signal 100 has been changed as shown in FIG.

If the target valve opening signal 100 is not changed in FIG. 4 (i), it is determined that the control valve 6 has become saturated, and the operation of the integrator 9 is performed as shown in FIG. 4 (j). At the same time, the output signal of the integrator 9 is fixed at the immediately preceding output value.

Conversely, if the target valve opening signal 100 has been changed in FIG. 4 (i), it is determined that the saturation state of the control valve 6 has been released, and the processing of FIGS. 4 (b) to 4 (e) is performed. Do.

In FIG. 5, (a) shows the operating state of the control valve 6, (b) shows the target valve opening signal 100, and (c) shows the output signal of the integrator 9, respectively.

In FIG. 5, "A" indicates the output signal of the integrator 9 according to the algorithm of FIG. 4, and "B" in FIG. 5 indicates that the operation of the integrator 9 is continued regardless of whether the control valve 6 is saturated. It is an output signal of the integrator 9 in the case.

At the time of "c" in FIG. 5, (a) in FIG.
When the conditions (f), (h) and (i) are satisfied, the integrator 9
5 stops, the output of the integrator 9 keeps a constant value as indicated by "d" in FIG.

When the target valve opening signal 100 is switched as shown by "e" in FIG. 5, the condition of (i) in FIG. 4 is not satisfied, so that the operation of the integrator 9 is restarted and the output of the integrator 9 The signal rises to the operating point indicated by "F" in FIG.
And the control valve 6 operates.

Accordingly, the time required for changing the target valve opening signal 100 and starting the response of the control valve 6 is "H" in FIG.
As shown in FIG. 5, it can be seen that the time required to start the response when the operation of the integrator 9 shown in FIG.

As a result, when the control valve 6 is saturated, the operation of the integrator 9 is stopped, thereby changing the target valve opening signal 100 to reduce the time until the control valve 6 starts responding. It becomes possible to shorten.

In the embodiment shown in FIG. 1, the subtractor 1 is a subtracter for subtracting a digital signal. Of course, the subtractor 1 subtracts the target valve opening signal 100 and the valve opening signal 101 at the time of an analog signal. The signal may be A / D converted and taken into the control circuit 2a.

[0076]

As is apparent from the above description,
According to the present invention, the following effects can be obtained. By reducing the integration time of the integrator when the control valve is saturated, or by stopping the operation of the integrator, the response of the control valve to a change in the target valve opening signal even when the integrator is saturated. A valve positioner that can reduce the time can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of a valve positioner according to the present invention.

FIG. 2 is a flowchart illustrating an operation of a control circuit.

FIG. 3 is a timing chart illustrating an operation corresponding to the flowchart of FIG. 2;

FIG. 4 is a flowchart illustrating the operation of the control circuit.

FIG. 5 is a timing chart for explaining an operation corresponding to the flowchart of FIG. 4;

FIG. 6 is a configuration block diagram illustrating an example of a conventional valve positioner.

FIG. 7 is a block diagram illustrating PID control of a valve positioner.

FIG. 8 is a timing chart illustrating states.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Subtractor 2, 2a Control circuit 3 D / A converter 4 Torque motor 5 Pilot relay 6 Control valve 7 Valve opening detector 8 A / D converter 9 Integrator 10 Proportional unit 11 Differentiator 12 Amplifier 13 Operation amount 14 Operating amount limiter 50, 50a Control means 51 Operating means 52 Detecting means 100 Target valve opening signal 101 Valve opening signal

Claims (3)

(57) [Claims] 1. A valve positioner for controlling the control valve by air pressure so that the valve opening of the control valve coincides with a target valve opening, detection means for detecting the valve opening of the control valve, and the control valve. Operating means for operating the valve opening degree, and controlling the operating means so that the output of the detecting means coincides with the target valve opening degree, and the output of the detecting means.
It does not change at a constant width, and the output of the detection means and the
The state where the deviation from the target valve opening exists more than a certain level is constant
It is determined that the control valve is saturated when the time has continued
To shorten the integration time and change the output of the detection means, or
The saturation of the control valve is released when the
And a control means for returning the integration time to the original value upon judging that the valve positioner has failed. 2. A valve positioner for controlling the control valve by air pressure so that the valve opening of the control valve coincides with a target valve opening, a detecting means for detecting the valve opening of the control valve, and the control valve. Operating means for operating the valve opening degree, and controlling the operating means so that the output of the detecting means and the target valve opening degree coincide with each other, and stopping the integration operation when the control valve is saturated. A valve positioner comprising control means. 3. The method according to claim 1, wherein the output of the detection means does not change within a certain width, and the state where the difference between the output of the detection means and the target valve opening degree exists for a certain time or more continues for a predetermined time. When the control valve is determined to be in a saturated state, the output signal of the detection means changes, or when the deviation becomes equal to or less than a predetermined value, or when the value of the target valve opening is changed, the control valve is changed. 3. The valve positioner according to claim 2, wherein it is determined that the saturated state has been released.