JP2003014157A - Valve positioner and control unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a valve positioner having excellent controllability capable of quickly controlling, while restricting the excessive quantity, and to provide a control unit used for the same. SOLUTION: This control unit comprises a reduction unit 21 for outputting a deviation between the input set value signal and the input valve opening measuring signal, a first integrator unit 24 for integrating the deviation, a proportion unit 23 for outputting a proportional value signal of the deviation, an addition unit 25 for adding the integration value signal and the proportional value signal to each other, an amplifier unit 26 for amplifying the output of the addition unit, a second integrator unit 27 for integrating the deviation in parallel with other units, and a valve opening condition discriminating unit 30 for discriminating the valve opening condition. While the valve opening condition discriminating unit 30 discriminates that the valve opening signal value is coming close to the set signal value, the second integrator unit 27 is reset, and while the valve opening discriminating unit 30 discriminates that the valve opening signal value is separating far from the set value, the second integrator unit 27 integrates the deviation, and this deviation is added to the addition unit, and computing for control is performed to restrict the excessive quantity.

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 used in process control so as to correspond to an external setting signal, and a controller usable for such a positioner. It is a thing.

[0002]

2. Description of the Related Art A valve positioner performs feedback control by a minor loop so that a signal from the outside such as a controller and a drive shaft position of a control valve operating unit are kept in a proportional relationship against an external force, and the operating unit is It is used in the control loop in order to fully exert its function. Therefore,
It is preferable that the entire operation unit has good responsiveness and has a simple transfer characteristic. Also, conditions such as size, type, and flow rate characteristics of the control valve differ according to the installation target, position, flow rate, etc., but the positioner attached to the control valve may not be designed and manufactured according to each target. It is designed to be used as commonly as possible due to the high cost. For this reason, the controller incorporated in the valve positioner is configured to perform so-called PID control that combines proportional-plus-integral-derivative operations, and optimizes and uses parameters such as the proportional coefficient, the integral time, and the derivative time for each object.

Although the overshoot amount, the rise time, and the settling time can be used as an index indicating the quality of control that is a target for adjusting the control parameter, if one of the rise time and the overshoot amount is small, the other becomes large. If the target is critical damping (limit braking), which is related, and that is settled fastest under the condition that there is no overshoot, the settling time becomes considerably long. In the valve positioner using the PID control, if the valve opening degree becomes excessive, in order to perform the reversing operation in the target value direction, it is necessary to wait until a strong operation output that cancels the inertial force and the static friction force generated in the operation unit is generated. However, there is a tendency that the settling time becomes longer. In addition, once overshooting occurs, there is a case where overshooting occurs in the opposite direction due to the force that returns the overshooting, and this is repeated, and the control does not converge. In this way, the quality of control must be compromised somewhere, and what is to be optimally adjusted depends on the characteristics of the controlled object and the designer's judgment.

The PID control method is a technique already established in the classical control theory, and optimum adjustment can be easily performed by knowing the transfer function for each element. However, it is not easy to analytically obtain the transfer function for each element in the control loop, and since the actual object usually includes nonlinear characteristics, the exact transfer function cannot be obtained. For this reason, the optimum adjustment parameters are actually obtained using an approximation method based on a field test such as the step response method or the limit sensitivity method. Therefore, the optimum value of the control parameter of the valve positioner must be determined by performing a thorough test for each control valve in which the positioner is incorporated.

When the electronic controller and the pneumatic control valve are combined, an electropneumatic positioner that performs control calculation by an electronic logic circuit is often incorporated in the control valve. Since the control logic can be selected relatively freely in such an electronic circuit, a good control result can be obtained by incorporating an appropriate process in accordance with the characteristics of the control system.

For example, in Japanese Patent No. 3057635, the integration time is shortened when it is detected that the control valve is fully closed or fully opened, and when it is released, the integration time in the normal control state is reduced. A reversible valve positioner is disclosed. This invention was made by paying attention to the fact that when the valve is fully closed and fully opened, the integrator integrates up to the saturation point, so the response becomes sluggish when returning the valve to the intermediate position. By returning it, the response characteristic of the control valve can be improved. However, the disclosed invention improves the responsiveness when the control valve reaches both end positions of the movable region, and does not relate to the controllability in the intermediate position which is important in the normal control operation.

Further, Japanese Patent No. 3039267 discloses that
A valve positioner is disclosed that switches control parameters such as a proportional coefficient according to the polarity of the control deviation or the polarity of the primary difference of the control deviation to perform control calculation. With the valve positioner according to the disclosed invention, when the transfer characteristics differ depending on the driving direction of the valve, it is possible to detect the increasing / decreasing direction of the valve opening degree and perform control suitable for each transfer characteristic. However, the disclosed invention is designed so that the optimum PID control operation can be performed even when the drive direction of the control valve is switched, and it is not possible to avoid the restriction of the control performance due to the linearity of the PID control. . In addition, it is inevitable that each time the control valves to be combined are changed, the rigorous actual experiment required to accurately set the optimum parameters is repeated.

[0008]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a valve positioner having an excellent controllability that can settle more quickly while suppressing an overshoot amount, and a controller that can be applied to such a valve positioner. Is to provide.

[0009]

A valve positioner of the present invention integrates a subtractor which inputs a set value signal and a valve opening measurement signal of a control valve and outputs a deviation obtained by subtracting the latter from the former. A first integrator which outputs a first integrated value signal, a proportional device which is connected in parallel with the first integrator and outputs a proportional value signal proportional to the deviation, and a first integrated value signal and a proportional value signal are input and added. Corresponding to a set value given from the outside by including an adder for outputting the output and an amplifier for multiplying the output of the adder by a predetermined coefficient and outputting the control signal to output an operation signal. To control the valve opening of the control valve.

In order to solve the above problems, in the valve positioner of the present invention, the controller is further arranged in parallel with the first integrator and integrates the deviation to output a second integrated value signal.
Equipped with an integrator and a valve opening state discriminator that determines the valve opening state by inputting the valve opening signal and the set value signal. The second integrator sets the integrated value to a predetermined initial value such as a zero value while it is determined that the value is approaching, and conversely, the second integrator integrates the deviation and outputs the output while it is determined that the value is approaching. It is characterized in that the control calculation is performed by adding it to the adder.

According to the valve positioner of the present invention, while the valve opening is approaching the set value, the operation of the second integrator is stopped and the normal proportional-plus-integral operation selected so as to match the control valve characteristic. Make the appropriate adjustments using. However, during a period in which the valve opening exceeds the set value and is moving away from the set value, the second integrator is operated to add the second integrated value that integrates the overshoot, so that the force in the braking direction that suppresses the overshoot is weighted. Therefore, it is possible to suppress the overshoot amount generated by the conventional proportional-plus-integral operation. When the valve opening has passed the extreme value and is about to return to the set value again, the operation of the second integrator is stopped.

In the valve positioner of the present invention, the overshoot amount becomes small as compared with the proportional-plus-integral operation executed by using the proportional unit and the first integrator, so that when the valve opening degree changes in the return direction after overshooting. The amount of overshoot in the opposite direction is significantly reduced. Therefore, the settling time to converge within a predetermined deviation is significantly shortened. Further, since the overshoot amount can be reduced by the second integrator, the response of the system can be improved by selecting the control parameters of the proportional unit and the first integrator so as to shorten the overshoot time.

The second integrator in the valve positioner of the present invention acts to reduce the overshoot by integrating the overshoot only when the overshoot of the valve opening is increasing. Also, since it does not work while the overshoot decreases,
The deviation before reaching the set value as in the integrator in the linear control has no influence on the overshoot suppressing action, so that the overshoot in the opposite direction is not increased. Therefore, since it has the effect of suppressing overshooting regardless of the transfer function of the control valve, it is sufficient to select an appropriately large integration time,
Even when the type or capacity of the control valve changes and the proportional-plus-integral parameter of the controller changes, the same second integrator can be applied without readjustment. In order to increase the adjusting effect of the second integrator, it is preferable to select an integration time shorter than the integration time of the first integrator.

In the valve positioner of the present invention, since the second integrator having the unique function as described above is attached to the controller, the overshoot amount is small and the settling time is small as compared with the conventional linear control method. Can be provided with a good response. Therefore, when the control valve incorporating the valve positioner of the present invention is used, the control valve as an element in the process control system has less influence on the control performance, and good control is facilitated. Further, it has a great applicability and can be easily applied to various control valves.

In the valve positioner of the present invention, the proportional unit, the first integrator, the second integrator, the amplifier and the like are shown as independent elements, respectively. It goes without saying that they can be assembled as individual electronic circuits. Further, control operation can be performed by logical operation using a logic circuit or a microcomputer. Further, the controller may be provided with a differentiation element so that control by proportional-plus-integral-derivative operation can be performed.

A second valve positioner of the present invention is a valve positioner for controlling the valve opening of a control valve so as to correspond to a set value given from the outside, and receives a set value signal and A / D converts it. A set value signal A / D converter that outputs a target opening signal value and a valve opening signal A / D converter that receives the valve opening signal of the control valve and A / D converts it to output a valve opening position signal value. And a control operation unit, and a control operation signal D / A conversion unit that receives the operation signal value output from the control operation unit and performs D / A conversion to output the operation signal.

The control calculation unit includes a subtracting means for calculating a deviation obtained by subtracting the valve opening position signal value from the valve opening position target signal value, a proportional means for calculating a proportional value of the deviation, and a first integral for the deviation. A first integrating means that applies a coefficient to perform integration to calculate a first integrated value, and a second integration coefficient that acts on the deviation to perform integration
Second integration means for calculating an integrated value, deviation polarity determination means for determining the polarity of the deviation, and valve opening for calculating the valve opening difference by subtracting the value of the valve opening position signal value for a predetermined time before Degree difference calculating means, adding means for adding the proportional value of the deviation, the first integrated value and the second integrated value, and an operation amount calculating means for multiplying the addition result by a predetermined coefficient to perform control operation and output as an operation value. Equipped with.

When the deviation polarity determination means determines that the deviation polarity is negative, that is, the valve opening position is larger than the set value, and the valve opening difference is a positive value, that is, the valve opening is increasing, or If the deviation polarity is positive, that is, it is determined that the valve opening position is smaller than the set value and the valve opening difference is a negative value, that is, the valve opening is becoming smaller,
The second integrated value is added and a control calculation is performed to obtain an operation value. When the deviation polarity determination unit determines that the deviation polarity is positive and the valve opening difference is a positive value, or when the deviation polarity is determined to be negative and the valve opening difference is a negative value, the second
It is characterized in that the integrated value is initialized and a control operation is performed to obtain an operation value.

A second valve positioner according to the present invention is provided with a control arithmetic unit so that main control arithmetic operations are executed by logical operations. Since the control operation executed by the control operation unit is the same as that executed by the first valve positioner of the present invention, the same operation and effect as those described above can be obtained. The control calculation unit may further include a differentiating unit that differentiates the deviation to calculate a differential value and supplies the differential value to the adding unit. Moreover, it is preferable that the control calculation unit is configured to be executed by a microcomputer. Further, the entire controller including the A / D converter and the like may be integrated on the printed board. In this way, by using the electronic circuit, the selectivity of the control logic is remarkably improved, the volume for installation is reduced, and the installation position can be freely selected, making it easy to adjust the parameters. Therefore, the positioner becomes smaller.

Next, the controller according to the present invention outputs a deviation obtained by subtracting the latter from the former by inputting the set value signal and the control amount signal, and a first integrated value signal obtained by integrating the obtained deviation. A first integrator, a proportional device connected in parallel with the first integrator for outputting a proportional value signal proportional to the deviation, and an adder for inputting and adding the first integrated value signal and the proportional value signal A controller that includes an amplifier that multiplies the output of the adder by a predetermined coefficient and outputs the result, performs a control calculation, and outputs an operation signal. In order to solve the above problems, the controller of the present invention further includes a second integrator which is arranged in parallel with the first integrator and which integrates the above deviation to output a second integrated value signal; and a control amount signal. And a set value signal to determine the state of the controlled variable. Then, the second integrator initializes the integrated value while the controlled variable state determiner determines that the value of the controlled variable signal is approaching the value of the set value signal, and conversely the The two integrator is characterized by integrating the deviation and adding the output to the adder. The subtractor, the proportional unit, the first integrator, the second integrator, and the controlled variable state discriminator may be configured by a microcomputer.

The controller according to the present invention is a controller suitable for the valve positioner according to the present invention. However, by applying it to various control systems which require similar control performance, the overshoot amount is small and the settling time is small. Good feedback control can be achieved. Further, in the case of controlling by incorporating only linear elements in the controller, the optimum proportional-integral-derivative parameter must be strictly determined based on the transfer characteristics that are clarified by conducting a field test in the field. On the other hand, if the controller of the present invention incorporating the second integrator having the above-mentioned special effect is used, the control state obtained when the second integrator is not used is always overshot. The amount can be reduced and the settling time can be shortened. Therefore, even for different controlled objects, if the control parameters are selected such that the rising speed is slightly faster and the oscillatory response is obtained only by the linear element, the controllability that is sufficiently satisfied by the action of the second integrator is obtained. be able to. Therefore, the use of the present invention also has the effect of facilitating the determination of control parameters.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing a control valve control system using a valve positioner of one embodiment of the present invention, FIG. 2 is a block diagram explaining the position in a process control system of this embodiment, and FIG. 3 is a control of this embodiment. 6 is a circuit diagram showing a typical circuit example of the container portion, FIG. 4 is a flow chart for explaining the operation logic of the second integrator of the present embodiment, FIG. 5 is an output diagram for explaining the output change of the second integrator, and FIG. 7 and FIG. 7 are output diagrams for explaining the effect when the present embodiment is applied.

FIG. 1 is a block diagram showing an operating portion formed by applying the valve positioner of this embodiment to a control valve. In addition, FIG. 2 is a block diagram showing an example of a feedback control system using an operation unit composed of a control valve. The valve positioner 1 according to the present embodiment is incorporated in the control valve 2 and has an operating portion 3 including a local feedback control system.
And adjusting the valve opening of the control valve to a value corresponding to the control output of the controller 4 to adjust the flow rate of the fluid passing through the control valve. The adjusted fluid flow rate acts on the controlled object 5 as an operation amount to control the controlled variable of the controlled object. The control amount is the detector 6
Detected by and supplied to the controller 4. The controller 4 performs a predetermined control calculation on the deviation from the target value to calculate an operation amount for eliminating the deviation, and supplies the operation amount to the operation unit 3 as a target value of the valve opening.

As shown in FIG. 1, the valve positioner 1 comprises a controller 10, an electropneumatic converter 41, a pneumatic pneumatic pilot valve 43 and a valve opening sensor 45, and is used in combination with the control valve 2. The electropneumatic converter 41 is a signal converter that receives the electric output signal of the controller 10 and outputs a corresponding pressure-pneumatic signal. The pilot valve 43 is a drive air source that receives a supply of compressed air from a compressed air source and supplies a large amount of air having a pressure corresponding to the compressed air signal to drive the control valve 2. The valve opening sensor 45 is a valve opening converter that detects the valve opening of the control valve via a link mechanism provided on the valve stem of the control valve 2 and outputs a measurement signal.

The controller 10 is a set value signal A / D converter 1
1, control operation signal D / A converter 12, valve opening signal A / D
The converter 13 and the control calculator 20 are provided. The set value signal A / D converter 11 converts the valve opening target value analog signal of the control valve 2 output from the controller 4 of the process control system into a digital set value signal SV suitable for a control calculation unit composed of a logic circuit. The control operation signal D / A converter 12 converts the digital operation value signal output from the control calculation unit 20 into an analog operation signal CV suitable for the electropneumatic converter 41, the valve opening signal A The / D converter 13 converts the analog output of the valve opening sensor 45 into a digital valve opening signal PV suitable for the control calculation unit 20.

The control calculator 20 includes a subtracter 21 and a differentiator 2
2, a proportional unit 23, a first integrator 24, an adder 25, an amplifier 26, a second integrator 27, and a control amount state determination unit 30. The subtracter 21 inputs the set value signal SV and the valve opening signal PV and subtracts the latter from the former, and the control deviation E =
Calculate and output SV-PV. The differentiator 22 differentiates the deviation E according to the set differential time Td and outputs the value obtained. The proportional unit 23 has a proportional coefficient Kp designated as a proportional band.
Then, the proportional value of the deviation E is output. Further, the first integrator 24 integrates the deviation E according to the designated integration time Ti and outputs it as a first integrated value. The outputs of these arithmetic elements are superimposed by the adder 25 and output as the operation signal CV of an appropriate scale by the amplifier 26.

FIG. 3 shows an arithmetic circuit 1 used in the control arithmetic unit.
FIG. 3 is a circuit diagram showing an example of a circuit that can actually perform the operation shown in FIG. 1 as an example. The arithmetic circuit shown in the figure is a combination of an amplifier 51 with an input impedance (Zi) 52 and a feedback impedance (Zf). The relationship between the input voltage ei and the output voltage eo is eo / ei = Zf /
It is represented by Zi. Feedback impedance (Z
f) is a proportional unit (Zfp) 53, a first integrator (Zfi)
54, a differentiator (Zfd) 55, and a capacitive element (Ci2) 56 as a second integrator are further connected in parallel.

In conventional electric regulators and pneumatic regulators, an amplifier for proportional-plus-integral-derivative operation is often used for the convenience of the circuit. In this case, the proportional coefficient of the proportioner is set to 1, and the differential value, After adding the integral value and the proportional value, they are multiplied by the proportional coefficient and output. Also in this embodiment, when utilizing the technical knowledge accumulated by the conventional regulator, the amplification factor of the amplifier 26 is set to the proportional coefficient Kp, the proportional coefficient in the proportional device 23 is set to 1, and the adder 25 is used. It is also possible to uniformly multiply the signals after addition by a proportional coefficient and output.

The capacitive element 56 of the second integrator is provided with a discharge switch 57 for short-circuiting both pole terminals and a connection switch 58 for shutting off the output of the integrated value. The two switches are interlocked with each other in opposite directions. It is configured to open and close, and the discharge switch 57 and the connection switch 58 are controlled by the controlled variable state determination unit 30. The second integrator 27 controls the control deviation E
Is added based on the integration time Ti2 and added to the input of the adder 25 as the second integrated value. However, the control amount state determination unit 30 is attached and the state of the valve opening determined by the control amount state determination unit 30 is determined. It is characterized by performing a special integration calculation based on. That is, the control deviation E is input and integrated only when the valve opening PV exceeds the set value SV and is deviating from the set value SV, and the obtained second integrated value is added to the adder 25, and conversely, the set value SV. When the value is approaching, the second integral value is set to zero so as not to affect the control calculation.

The control amount state determiner 30 includes a deviation polarity determiner 31 for determining the sign of the control deviation E, and a value PV (n-1) a predetermined time before the current value PV (n) of the valve opening position signal. And the valve opening difference ΔPV = PV (n) −PV (n−1)
And a determination device 33 that determines the valve opening state from these outputs, and determines whether the valve opening PV is approaching or moving away from the set value SV. Then, the second integrator 27 is controlled. In order to suppress the influence of noise and calculate an appropriate difference, it is necessary to use an appropriate time interval or average the valve opening signals. Further, instead of the difference, it is also possible to use the differential for the valve opening signal after passing through an appropriate filter.

FIG. 4 is a flow chart showing the logic executed by the controlled variable state discriminator 30. Referring to the flowchart of FIG. 4, the controlled variable state determiner 30 first inputs the output of the deviation polarity determiner 31 and checks whether the deviation E is positive or negative (S10). If the deviation E is positive, the valve opening PV is the set value S
Since it is smaller than V, the difference output Δ of the valve opening difference calculator 32
The positive or negative of PV is checked, and the process is selected according to the result (S20). When the valve opening PV is smaller than the set value SV, the valve opening PV approaches the set value SV when the valve opening PV decreases and approaches the set value SV when the valve opening PV increases.

Therefore, when the valve opening difference ΔPV is negative, the discharge switch 57 is opened and the connection switch 58 is short-circuited to cause the second integrator 27 to execute the integration of the deviation E, and another proportional-integral-derivative operation circuit. To supply the second integrated value output (S30). When the valve opening difference ΔPV is positive, the discharge switch 57 is closed and the connection switch 58 is opened to disconnect the second integrator 27 from the other proportional-plus-integral-differential operation circuit, and Capacity element C
The charge accumulated in i2 is discharged to reset the past accumulation (S40).

On the other hand, when the deviation E is negative, the positive / negative of the differential output ΔPV of the valve opening difference calculator 32 is checked on the assumption that the valve opening PV exceeds the set value SV upward (S5).
0). When the valve opening PV exceeds the set value SV, the valve opening PV moves away from the set value SV when the valve opening PV increases, and approaches the set value SV when the valve opening PV decreases. Therefore, when the valve opening difference ΔPV is positive, the second integrator 2
7 is executed to integrate the deviation E, and a second integrated value output is supplied to the control arithmetic circuit (S30). Further, when the valve opening difference ΔPV is negative, the second integrator 27 is disconnected from the control arithmetic circuit and the second integrator 27 is reset (S40).

In this way, the state of the valve opening is judged by the control amount state discriminator 30, and only when the valve opening PV is approaching the set value SV, the differentiator 22, the proportional unit 23, and the first integrator. The second integrator 27 is weighted on the conventional proportional-integral-derivative operation using 24, and under other conditions, the control operation is performed only by the conventional proportional-integral-derivative operation (S60).

FIG. 5 shows a change in the valve opening PV when the valve opening set value SV is changed stepwise in the valve positioner using the controller of this embodiment, and a control amount corresponding to the change in the valve opening. It is a waveform diagram which shows typically the output change of the state discriminator 30 and the 2nd integrator 27. When the set value changes to a large value, the valve opening degree increases accordingly (region a). In the area a, the second integrator 27 is not used, but the differentiator 22, the proportionalizer 23, and the first integrator 24 are used for the control calculation. If the proportional-integral-derivative parameter is selected so that the rise time will be slightly shorter, the valve opening will exceed the set value and go too far. Due to the influence of the first integrator 24 and the delay element included in the controller 10, the controller 10 controls the control valve 2 based on the accumulated calculation result of the past deviation E even when the valve opening reaches the set value. It outputs an operation signal that acts in the opening direction.

The controller 10 of this embodiment further includes a second integrator 27 and a controlled variable state determiner 30. Therefore,
In this region b, the output of the controlled variable state discriminator 30 is turned on, and the second integrator 27 integrates the deviation E to output a gradually larger value, so that the controller 10 increases the valve opening degree as the deviation E increases. The operation signal CV for accelerating in the direction of decreasing is output. In the region b from when the valve opening exceeds the set value to when it reaches the maximum value, the controller 10 changes the operation signal in the direction in which the deviation E decreases as the sign of the deviation E changes. Eventually, the valve opening takes a maximum value, reverses, and decreases toward the set value.

In the region c from when the valve opening degree starts to decrease past the extreme value to when it reaches the set value, the controlled variable state discriminator 3 is provided.
Since the output of 0 is turned off and the second integrator 27 is reset, the control calculator adjusts the valve opening based on the normal proportional-integral-derivative operation. In this area c, the action of the second integrator 27 disappears, so the second integrated value of the deviation E in the area b before that does not affect the control calculation, and the deviation E in that area b is the normal PID. It is smaller than the case of only calculation. Therefore, the force for reducing the valve opening becomes smaller, the momentum when crossing the set value downwards becomes weaker, and the downward overshoot amount decreases.

In the region d in which the valve opening degree falls below the set value and the valve opening degree moves away from the set value, the output of the controlled variable state discriminator 30 is turned on again, and the second integrator 27 determines the deviation E. Integrate and output. For this reason, the control calculator outputs an operation signal for accelerating in the direction of decreasing the valve opening as the deviation increases, so that the valve opening eventually reaches the minimum value and is inverted toward the set value. In this way, when the valve opening exceeds the deviation and the deviation increases, the overshoot amount is suppressed as compared with the normal control operation, and the suppression effect is accumulated each time the overshoot is repeated, so that the settling time is significantly shortened.

The action of the second integrator 27 is the integration time T
The shorter i2 is, the larger it can be adjusted by setting. Unlike the normal integration element, the second integrator 27 integrates only the deviation E within the region in which the valve opening is reset while the valve opening approaches the set value and changes away from the set value to perform the control calculation. To work. For this reason, since it has only the effect of suppressing the generated deviation E, the differentiator 22, the proportionalizer 23, the first
Regardless of the proportional-plus-integral-derivative parameter used for the integrator 24, the integration time Ti2 can be selected to be a sufficiently small value. Therefore, even when the valve positioner is applied to control valves having different specifications, it can be used without changing the integration time Ti2.

6 and 7 are output waveform diagrams showing an example in which the control valve is controlled by applying this embodiment. In the figure, the horizontal axis represents time and the vertical axis represents the output signal, and the set value is changed in 25% steps, and the indial response of the valve opening is observed. The graph shown by the dotted line in the figure shows the change in valve opening when the control valve is controlled without using the second integrator, and the graph shown by the solid line shows that when the controller of this embodiment incorporating the second integrator is used. This is a change in valve opening.

In the case of FIG. 6, a second integrator having an integration time of 5 seconds is made to act on a control parameter selected so as to behave in a somewhat oscillatory manner. The overshoot amount is reduced from 71% to 45% by about 0.6 times, and the settling time is reduced from 22 seconds to about 9 seconds by about 0.4 times, demonstrating the effect of the present invention. Further, in the case of FIG. 7, the same second integrator as in FIG. 6 is made to act on the selected control parameter that is appropriate for the normal PID operation. Also in this case, the overshoot amount is reduced from 46% to 24% by about 0.5 times, and the settling time is reduced from 5.1 seconds to 3.4 seconds by about 0.66 times.

Although the control calculation based on the PID operation is used in the description of the above embodiment, the control calculation based on proportional and integral may be used instead of differential depending on the specifications of the control valve. Further, in the above description using the drawings, in order to facilitate understanding, a proportional-integral-derivative calculation element 2 is formed by an analog calculation circuit.
Although 2, 23, 24, 25, 26, and 27 are configured, they may be configured by a computer-executable program or digital logic circuit. In the case of assembling the control logic by digital arithmetic processing, the handling becomes easy and the effective control can be found by simply changing the circuit configuration and arithmetic parameters.

Furthermore, since the circuit configuration is simple and compact by digitization, there is an advantage that the entire valve positioner is compact and inexpensive. In particular, in the case of using a microcomputer including the controlled variable state determination unit 30 composed of a simple digital logic circuit, it is possible to obtain a very efficient and compact device. Further, the set value signal A / D converter 11, the control operation signal D / A converter 12, the valve opening signal A / D converter 13, and the digital arithmetic circuit 2
When 0 is mounted on a single printed circuit board and incorporated, the size of the valve positioner can be significantly reduced.

Further, in the present embodiment, the controller of the present invention is incorporated in the valve positioner and used in the minor loop. However, the same effect can be obtained by using the controller as a main loop in a normal feedback control system. Needless to say, it can be obtained.

[0045]

As described above, according to the present invention, when the feedback control of the process is performed, the function of the second integrator suppresses the overshoot and shortens the settling time to obtain a good control result. Obtainable. Especially when it is applied to a controller of a valve positioner incorporated in a control valve, the controllability of the control valve is remarkably improved, and a good control system with good responsiveness can be constructed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a control valve control system using a valve positioner according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating positions in the process control system of the present embodiment.

FIG. 3 is a circuit diagram showing a typical circuit example of a controller portion of this embodiment.

FIG. 4 is a flowchart illustrating the operation logic of the second integrator of this embodiment.

FIG. 5 is an output diagram illustrating a change in output of a second integrator.

FIG. 6 is an output diagram illustrating an effect when the present embodiment is applied.

FIG. 7 is a second diagram for explaining the effect of applying this embodiment.
FIG.

[Explanation of symbols]

1 valve positioner 2 control valve 3 operation part 4 regulator 5 controlled objects 6 detector 10 controller 11 Set value signal A / D converter 12 Control operation signal D / A converter 13 Valve opening signal A / D converter 20 Control calculator 21 Subtractor 22 Differentiator 23 Proportionator 24 1st integrator 25 adder 26 Amplifier 27 Second integrator 30 Control quantity state determination unit 41 Electro-pneumatic converter 43 Pneumatic pilot valve 45 valve opening sensor 51 amplifier 52 Input impedance (Zi) 53 Proportional device (Zfp) 54 First integrator (Zfi) 55 Differentiator (Zfd) 56 Capacitance element (Ci2) 57 discharge switch 58 Connection switch

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 3H065 BB12                 5H004 GA03 GA11 GB01 HA07 HB07                       JA03 JB19 KA69 KB02 KB04                       KB06 KB39 KC39 LA05 LA17                       LB05 LB06 MA41 MA42 MA43

Claims (7)

[Claims] 1. A subtracter which inputs a set value signal and a valve opening measurement signal of a control valve and outputs a deviation obtained by subtracting the latter from the former, and a first integral which outputs a first integrated value signal obtained by integrating the deviation. A proportional unit that is connected in parallel with the first integrator and outputs a proportional value signal proportional to the deviation; and an adder that inputs the first integrated value signal and the proportional value signal, adds them, and outputs the result. A controller that includes an amplifier that multiplies an output of the adder by a predetermined coefficient and outputs the operation signal, the controller outputting a control signal and outputting an operation signal. A second integrator that outputs an integrated second integrated value signal, and a valve opening state discriminator that inputs the valve opening signal and the setting value signal and determines the state of the valve opening are provided. Degree discriminator determines that the value of the valve opening signal is approaching the value of the set value signal. The second integrator initializes the integrated value while the second integrator is on the other hand
A valve positioner that includes a controller that integrates the deviation and adds the output to the adder, and controls the valve opening of the control valve so as to correspond to a set value given from the outside. 2. A set value signal A / D converter for receiving a set value signal and A / D converting it to output a valve opening target signal value, and an A / D converter for receiving a valve opening signal of a control valve. A valve opening signal A / D converter that outputs a valve opening position signal value, a control calculator,
A controller provided with a control operation signal D / A conversion means for receiving an operation signal value output from the control operation section, converting the value, and outputting an operation signal, wherein the control operation section opens the valve. Degree subtraction means for subtracting the valve opening position signal value from the degree position target signal value to calculate a deviation, proportional means for calculating a proportional value of the deviation, and a first integration coefficient acting on the deviation to perform integration. 1
First integration means for calculating an integrated value, second integration means for applying a second integration coefficient to the deviation to perform integration to calculate a second integrated value, and deviation polarity determination means for determining the polarity of the deviation, A valve opening difference calculation means for calculating a valve opening difference by subtracting a value of the valve opening position signal value from a current value before a predetermined time, and the proportional value, the first integral value and the second integral value are added. Adding means,
And a control calculation means for performing a control calculation by multiplying the addition result by a predetermined coefficient and outputting it as an operation value, wherein the deviation polarity is determined to be negative by the deviation polarity determination means and the valve opening difference is positive. When it is a value or when the deviation polarity is determined to be positive and the valve opening difference is a negative value,
When the deviation polarity determining unit determines that the deviation polarity is positive and the valve opening difference is a positive value, or the deviation polarity is When it is determined to be negative and the valve opening difference is a negative value, the controller is characterized in that the second integrated value is initialized and the control calculation is performed to obtain an operation value. A valve positioner that controls the valve opening of the control valve to correspond to a given set value. 3. The valve positioner according to claim 2, wherein the control calculation unit further includes a differentiating unit that differentiates the deviation to calculate a differential value and supplies the differential value to the adding unit. 4. The valve positioner according to claim 2, wherein the control calculation unit is executed by a microcomputer. 5. The valve positioner according to claim 2, wherein the controller is integrated on a printed circuit board. 6. A subtracter which inputs a set value signal and a control amount signal and outputs a deviation obtained by subtracting the latter from the former, a first integrator which outputs a first integrated value signal obtained by integrating the deviation, and a first integrator. 1 integrator connected in parallel to output a proportional value signal proportional to the deviation, an adder for inputting and adding the first integrated value signal and the proportional value signal, and outputting, and an output of the adder A controller that outputs an operation signal by performing a control calculation, comprising an amplifier that outputs a signal by multiplying by a predetermined coefficient.
A second integrator that is arranged in parallel with the first integrator and outputs a second integrated value signal that integrates the deviation; a control that inputs the control amount signal and the set value signal and determines the state of the control amount The second integrator initializes an integrated value while the control amount state determiner determines that the value of the control amount signal is approaching the value of the set value signal, and The controller characterized in that the second integrator integrates the deviation and adds the output to the adder while it is determined that the distance is increasing. 7. The subtractor, the proportional unit, the first integrator, and the second unit.
7. The controller according to claim 6, wherein the integrator and the controlled variable state discriminator are implemented by a microcomputer.