JPH07103202A - Valve positioner - Google Patents

Abstract

PURPOSE:To realize the optimum stability and responsiveness by generating a starting signal for such as setting response measurement or outputting a specified set value, measuring respective time differences from a reference time to the final time of regulating valve displacement, and/from then starting time of the valve displacement, and calculating/setting a control parameter based on those etc. CONSTITUTION:A first starting signal SS1 for setting a response measurement condition, and a reference time for starting the setting are given by a setting start signal generation means 20, and a second starting signal SS2 for outputting a specified set value, and a third starting signal SS3 for outputting a specified set value by receiving a displacement end signal DF of a regulation valve are generated by said means 20. A first time difference from the reference time to the time for receiving the displacment end signal DF, and a second time difference from the reference time to the time for starting valve displacement by outputting the third starting signal SS3 are measured by a time measuring means 22. A control parameter is calculated based on the time defference signal by a parameter setting means 23, and the control parameter is set in a control calculation means 21 by a parameter setting means 24. Consequently, the control parameter can be automatically set on the regulation valve, and thereby optimum stability and responsiveness can be secured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a valve positioner used in a control valve for controlling the flow rate of various fluids provided in a plant, and more particularly to the friction force of the gland packing of the control valve and the capacity of the drive section. The present invention relates to a valve positioner improved so that optimum stability and response characteristics can always be realized.

[0002]

2. Description of the Related Art FIG. 4 is a configuration diagram showing a configuration of a conventional valve positioner. A current signal I _i of 4 to 20 mA is input to the input terminal 1 from a controller or the like via two transmission lines (not shown).

[0003] Input unit 10 is to create a constant voltage E _b as a circuit power supply used in this positioner 15 by using the current signal I _i, the voltage signal V _i corresponding to the current signal I _i at the same time
Is output.

This voltage signal V _i is input to one end of the input of the control calculation means 11 and the other end of the valve opening detection means 1
The feedback signal V _f output from 3 is input. The control calculation means 11 calculates the deviation between the voltage signal V _i and the feedback signal V _f and outputs the drive signal V _d to the air pressure generation means 12 at the output end so as to eliminate this deviation.

[0005] Pneumatic generating means 12 is supplied with supply air P _S, the drive signal is applied to V _d with the supply air pressure P _S, for example, in a driving circuit for driving an electromagnetic drive actuator, it flows along with this A displacement corresponding to the drive current is applied to the nozzle / flapper mechanism to convert it into an air pressure signal, which is amplified by a pilot relay or the like and output to the control valve drive unit 3 of the control valve 2 as the operating pressure P ₀ .

The control valve 2 moves its stem 4 up and down in response to this operating pressure P ₀ . This movement changes the valve opening degree V _A of the control valve 2, and this movement is also output to the valve opening degree detection means 13.

This valve opening degree V _A is converted into a feedback signal V _f as a corresponding electric signal and output to the control calculation means 11 to form a feedback loop as a whole. Therefore, the stem position of the control valve is directly proportional to the current signal I _i transmitted from the controller.

The valve positioner thus constructed has good stem position accuracy even if it is a control valve having different diameters and characteristics, that is, the steady deviation is small, and the response is fast.
High control performance that is less likely to cause oscillation is desired.

However, the actual characteristic of the control valve is
Since it largely varies depending on the drive unit capacity, the hysteresis due to the frictional force of the gland packing, etc., the steady state deviation is small for all kinds of control valves, and high control performance is realized. In addition to the proportional operation (P operation), proportional differential operation, integral operation, etc. are performed to perform characteristic compensation.

Specifically, in a control valve having a large drive capacity and not so much hysteresis, the time constant of the control valve itself is sufficiently larger than the time constant inside the positioner 15, so that the control system has a higher order. It is difficult to become a system of.

Therefore, the loop gain can be increased to such an extent that the steady-state deviation does not cause a problem in performance, and the supply / exhaust capacity of the pilot relay can be increased, so that responsiveness and stability can be secured at the same time.

However, if this constant is applied to a control valve with a small drive capacity, the time constant of the control valve will be the positioner 1.
Since it is closer to that of No. 5, oscillation is likely to occur, and it is necessary to reduce the loop gain.

For this reason, since the steady-state deviation becomes a problem, it is necessary to compensate by the integral operation (I operation), and also the compensation by the differential operation (D operation) is necessary to secure the response characteristic.

As can be seen from the above, in the conventional positioner 15, the control parameters such as the gain and the time constant of the PID operation executed by the control calculation means 11 are adjusted for each control valve according to the hysteresis amount and the drive capacity. In this case, the parameter setting means 14 is manually adjusted and set by a switch or volume.

[0015]

However, the above positioner has the following problems. Since it is necessary to manually adjust and set the gain and time constant for each control valve, the number of man-hours for mounting the control valve is increased and the cost is increased.

Since it takes a lot of time to measure the size of the hysteresis, the size is actually estimated and set from the type of the gland packing, so that the optimum adjustment is difficult.
It was not always possible to obtain optimum characteristics.

Also, it is good if the capacity of the drive unit is known in advance, but if it is unknown, it is difficult or difficult to actually measure it. Couldn't get

[0018]

According to the present invention, a current signal for controlling the valve opening of a control valve and a valve opening signal related to the previous valve opening are provided as a structure for solving the above problems. In a valve positioner for controlling deviation of the valve opening, which is input through the valve opening detecting means and is calculated by the control calculating means, first setting of a preliminary state for response measurement is started.
A predetermined set value is received by receiving a start signal and a reference time for starting the setting and sending a predetermined set value and a second start signal and a displacement end signal notifying that the change in valve displacement of the previous control valve is zero. And a first time difference from the reference time to the reception of the displacement end signal and the setting start signal generating means for generating a third start signal for transmitting the signal. From the reference time to the time point at which the change of the valve displacement is started by the transmission of the third start signal, and the time measuring means for outputting the displacement end signal and the first time difference. And a parameter difference calculation means for calculating the optimum control parameter based on the received time difference signal of the second time difference, and a parameter setting for setting the previous control parameter in the previous control calculation means based on the calculation result. means It is obtained so as to include a.

[0019]

[Operation] The setting start signal generating means includes a first start signal for starting the setting of the preliminary state for response measurement, and a second start signal for giving a reference time for starting the setting and transmitting a predetermined set value. And a third start signal for sending a predetermined set value upon receipt of a displacement end signal indicating when the change in valve displacement of the control valve is zero.

Further, the time measuring means monitors the signal from the preceding valve opening degree detecting means, and the first time difference from the previous reference time to the reception of the previous displacement end signal and the third reference time from the previous reference time.
By transmitting the start signal, the second time difference until the point where the change in the valve displacement starts is measured, and the displacement end signal is output.

Furthermore, the parameter calculating means is the first
The time difference signal of the second time difference and the time difference is received, and the optimum control parameter is calculated based on these signals. And
The parameter setting means sets the above control parameter in the control calculation means for calculating the deviation between the current signal for controlling the valve opening of the control valve and the valve opening signal related to the previous valve opening based on this calculation result. To do. This makes it possible to automatically set optimum control parameters for all control valves.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing the configuration of one embodiment of the present invention. The parts having the same functions as those of the conventional valve positioner shown in FIG. 4 are designated by the same reference numerals, and the description thereof will be appropriately omitted.

The setting start signal generating means 20 outputs the first start signal SS ₁ , the second start signal SS ₂ and the third start signal SS ₃ to the control calculating means 21. Further, the second start signal S
S ₂ is also output to the time measuring means 22.

Of these, the first start signal SS ₁ is for response measurement such that the feedback signal V _f output from the valve opening detection means 13 is cut, for example, to set the valve opening V _A to the minimum. Is a signal for starting the setting of the preliminary state of.

The second start signal SS ₂ gives a reference time T _S for starting the setting by this sending and sends a predetermined set value for maximizing the valve opening degree V _A of the control valve 2. Signal to do.

The characteristic of the drive signal V _d / air supply capacity Q of the air pressure generating means 12 is the characteristic shown in FIG. 2, but this set value is saturated with a signal larger than the drive signal V _d ′ here. It is set as having characteristics.

Further, the third start signal SS ₃ is supplied to the control valve 2
When a change end signal DF is received from the time measuring means 22 for notifying when the change ΔV _A of the valve displacement is 0, the set value for changing the valve displacement in the direction opposite to the direction set by the previous set value is transmitted. .

The time measuring means 22 sends the time difference (T ₁ -T _S ) from the reference time T _S to the time T ₁ when the displacement end signal DF is received, and the third start signal SS ₃ to transmit the valve displacement. There is a direction set by the first setting value to measure a time difference between the time began to change in the direction T ₂ and the reference time T _S of reverse and (T ₂ -T _S).

Then, the parameter calculating means 23 receives these time differences (T ₁ -T _S ) and (T ₂ -T _S ), and uses them to obtain a relational expression or a setting which has been previously obtained by experiments or the like. Optimal gain, referring to tables etc.
Calculate or select the optimal time constant.

The optimum control parameter CP determined in this way is sent to the parameter setting means 24, where it is set as a control parameter required for calculation in the control calculation means 21. Note that these operations may be performed using a discrete circuit, but are performed using a microcomputer as needed.

Next, the operation of the embodiment configured as described above will be described with reference to the waveform chart shown in FIG. Prior to controlling the valve opening of the control valve, first, automatic parameter setting for obtaining optimum control characteristics is performed.

First, the setting start signal generator 20 outputs the first start signal SS ₁ to the control calculator 21 as shown in FIG. Thereby, for example, the feedback signal V _f
Is cut and the valve opening degree V _A is set to the minimum value as shown in FIG. The drive signal V _d output from the control calculation means 21 to the air pressure generation means 12 at this time is as shown in FIG. 3B, for example.

Next, after a lapse of a predetermined time, the second start signal SS ₂ (FIG. 3A) is output to the control calculation means 21. Thereby, the drive signal V corresponding to the predetermined set value
_d (FIG. 3 (b)) is output from the control calculation means 21 to the air pressure generation means 12 to try to increase the valve opening degree V _A (FIG. 3 (c)). At the same time, the second start signal SS ₂ is applied to the time measuring means 22 to give the reference time T _S for the time difference calculation.

When the second start signal SS ₂ (FIG. 3 (a)) is output, the valve opening degree starts increasing and reaches the maximum value. At that time T ₁ (FIG. 3 (c)), the valve opening degree is increased. since the change [Delta] V _a of V _a is eliminated, the time measuring means 22 outputs a displacement termination signal DF to the setting start signal generating means 20 detects this.

The time measuring means 22 uses this displacement end signal DF.
Is received, this time the drive signal V _dTo minimize
Set the original value (Fig. 3 (b)). However, this setting
Valve is not responded immediately to the
Opening V_AChange ΔV_AIs started (FIG. 3 (c)). time
The measuring means 22 starts at this starting point T₂To measure.

Therefore, since the time measuring means 22 can know the reference time T _S , the time point T ₁ and the time point T ₂ , the time differences (T ₁ -T _S ) and (T ₂ -T _S ) are calculated. can do.

Of these, the time difference (T ₁ -T _S ) corresponds to the time when the valve displacement changes from the minimum to the maximum while the supply air flow rate of the air pressure generating means 12 is saturated. It represents the capacity.

Further, the time differences (T ₁ -T _S ) and (T ₂ -T _S )
Difference, i.e., so that the leading so (T ₂ -T ₁₎ is equivalent to the time the air within the drive unit is not displaced even valve is evacuated, the hysteresis of the gland packing of the regulating valve.

In this way, the time difference measured by the time measuring means 22 is transferred to the parameter calculating means 23,
Here, calculation parameters such as the optimum gain and the optimum time constant are calculated, and the results are set in the control calculation means 21 via the parameter calculation means 24. After these calculation parameters are determined, these values are calculated by the control calculation means 2.
It is fixed at 1, and the valve opening degree V _A corresponding to the current signal I _i is controlled in an optimum state.

In this way, it is not necessary to estimate the hysteresis of various control valves or the capacity of the drive unit, or to manually set the optimum control parameters by measuring them by another means in advance, so that the adjustment work cost can be reduced. And because it can always set the optimum parameters, high accuracy,
A valve positioner having high-speed response and high stability can be realized.

[0041]

As described above in detail with reference to the embodiments, according to the present invention, various start signals are sent to the control calculation means and the time measurement means, and the control performance of the positioner is greatly affected by the response time difference of the control valve. Since the values corresponding to the hysteresis of the control valve and the displacement of the drive unit that are affected can be easily measured, and the optimum control parameters can be automatically set based on these values, the following effects can be expected.

When attaching the positioner to the control valve,
There is no need to measure the characteristics of the control valve using other measuring instruments or to manually adjust and set control parameters such as gain and time constant, thus reducing the work time.
Cost reduction is possible. The control parameter can be calculated or selected by actually measuring the value corresponding to the hysteresis of the control valve or the displacement of the drive unit, so that the optimum control parameter can always be set,
Optimal stability and response characteristics can be achieved for all control valves.

[Brief description of drawings]

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

FIG. 2 is a characteristic diagram showing characteristics of a drive signal / air supply capacity of the air pressure generating means shown in FIG.

FIG. 3 is a waveform diagram for explaining the operation of the embodiment shown in FIG.

FIG. 4 is a configuration diagram showing a configuration of a conventional valve positioner.

[Explanation of symbols]

2 control valve 3 control valve drive part 4 stem 10 input means 11, 21 control calculation means 12 air pressure generation means 13 valve opening detection means 14, 24 parameter setting means 20 setting start signal generation means 22 time measurement means 23 parameter calculation means SS ₁ 1st start signal SS ₂ 2nd start signal SS ₃ 3rd start signal DF Displacement end signal CP Control parameter

Claims (1)

[Claims] 1. A current signal for controlling the valve opening of a control valve and a valve opening signal related to the valve opening are input through a valve opening detecting means, and deviations of these signals are calculated by a control calculating means. In the valve positioner for controlling the valve opening, the first start signal for starting the setting of the preliminary state for response measurement and the second start signal for giving the reference time for starting the setting and sending the predetermined set value Setting start signal generating means for generating a start signal and a third start signal for transmitting a predetermined set value upon receipt of a displacement end signal indicating when the change in valve displacement of the control valve is zero; A first time difference from the reference time to the reception of the displacement end signal and a second time from the reference time to a time point at which the change of the valve displacement is started by sending the third start signal by monitoring the signal from the detection means. Measure the time difference and change Time measuring means for outputting an end signal; parameter calculating means for receiving the time difference signals of the first time difference and the second time difference and calculating optimum control parameters based on these signals; and controlling the control based on the calculation result. A valve positioner, comprising: parameter setting means for setting the control parameter in the computing means.