JPH04236601A - Process controller - Google Patents

Abstract

PURPOSE:To automatize the accurate control of small deviation by performing the feedback control of a process while automatically stepwise changing a gap. CONSTITUTION:When a gap GP is set at the time of PID control, a gap changing part 2 reduces a gap set value GP stepwise by GP at intervals of a certain time. A PID control part 1 compares the deviation between a target value SV and a process measured value PV taken into a measuring instrument Se with the gap GP given from the gap changing part 2 by a deviation comparing part 11. When this deviation is smaller than the gap GP, operation is not performed; but when it is larger than the gap GP, PID operation based on the deviation is performed by a PIV control part 12 to obtain a next manipulated variable MV. This variable MV is given to an operation end Pe to control the process.

Description

[Detailed description of the invention]

[Object of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process control device that performs feedback control of a process.

0003

[Prior Art] Conventionally, various control methods such as PID control, sample PID control, and others have been adopted for process control in various industries such as pulp and paper, petrochemical, and steel plants. The method generally changes the manipulated variable MV to the process in order to bring the process measured value PV closer to the process target value SV. In such a control method, a feedback control method is used in which the manipulated variable MV to the process is determined, and the resulting change in the process measurement value PV is detected, and then the next manipulated variable MV is determined.

[0004] This feedback control has the problem that an overshoot decrease occurs in which the process measured value PV exceeds or falls below the target value SV, and it takes time for the process to stabilize.

[0005] Therefore, as a countermeasure against this overshoot phenomenon, a method of setting a gap has been introduced. This gap setting method is based on the process measurement value P
The deviation between V and the target value SV is compared with a preset gap GP, and if the deviation is greater than or equal to the gap GP, the manipulated variable MV is determined and the process is operated; however, if the deviation is less than or equal to the gap GP, the process is operated. , this is a method in which the manipulated variable MV of feedback control is not output.

However, the conventional gap setting method is
This is a method in which the gap GP is set artificially and the change is also performed artificially.If you want the deviation to be 0, the gap GP
We had to take a step-by-step approach to artificially reduce the amount. Therefore, if strict control is to be performed, manual operation is required and there is a problem that it takes time.

[0007]

SUMMARY OF THE INVENTION As described above, in the conventional process control apparatus, manpower is required to change the gap, and automation of the process has been desired.

[0008] The present invention was made in view of the above-mentioned conventional problems, and it is possible to perform feedback control of the process while automatically changing the gap in stages, and to automatically perform strict control with small deviations. The purpose is to provide a process control device that can perform

[Configuration of the invention]

0010

[Means for Solving the Problems] The present invention provides a process control device that calculates a process operation amount based on a deviation between a process target value and a process measurement value, and performs feedback control of the process based on the operation amount. a gap setting means for setting a gap for the deviation between the process target value and the measured value; a gap reduction width setting means for setting a gap reduction width for gradually reducing the gap set by the gap setting means; The apparatus further includes a gap changing means for decreasing the gap set by the gap setting means stepwise by the reduction width set by the gap reduction width setting means every predetermined time period.

[0011]

In the process control apparatus of the present invention, the gap changing means gradually decreases the gap set by the gap setting means by the reduction width set by the gap reduction width setting means every predetermined period of time. Then, the gap changed by this gap changing means is compared with the deviation between the process measurement value and the target value, and if the deviation is greater than the gap, the process operation amount is calculated and the process is operated, and if the deviation is less than the gap, the process is operated. If the control operation is stopped,
Perform feedback control of the process.

[0012] In this way, while the process measurement value is far away from the target value and the deviation is large, a large gap is set and significant process control is performed, and as the process measurement value approaches the target value, the gap is gradually increased. small size and allow for strict control.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be explained in detail below with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the process control device of the present invention, which includes a PID control section 1 that is widely used for feedback control, and a gap GP for this PID control section 1 that is changed in stages and output. The gap changing section 2 is also provided.

The PID control unit 1 has a control target process P.
The target value SV of the state quantity is given, and the measured value PV of the state quantity is taken in from the process measuring instrument Se, PID calculation is performed on the deviation between these target value SV and the measured value PV, and the process This is the part that outputs the manipulated variable MV of the process to the process operation end Pe of the process, and the above deviation |SV-P
Compare V| with the gap GP to determine the PI of the next process.
A deviation comparator 11 determines whether to execute D control, and a PI
It is composed of a PID calculation section 12 that performs D calculation, obtains and outputs the manipulated variable MV.

The gap change unit 2 receives a gap change start command SS, a gap initial value GPo, and a gap that are automatically input in response to an input signal from an operator through a man-machine interface or a mode selection signal from the PID control unit 1 side. Using each of the decrease width ΔGP, decrease period t1 and gap lower limit value GPmin as input data, the gap G
The input/output controller 21 performs input/output control, the timer 22 performs time management, and according to the time-up signal of this timer 22, ΔGP is output from the gap GPo at regular intervals t1. It is comprised of an arithmetic unit 23 that performs subtraction and outputs the changed gap GP, and a comparison unit 24 that compares and determines whether this gap GP is smaller than the gap lower limit value GPmin.

Next, the operation of the process control device having the above configuration will be explained. In the PID control unit 1, the deviation comparison unit 11 first calculates the deviation |SV−PV| between the target value SV given in advance and the process measurement value PV taken from the measuring device Se of the process P, and calculates the deviation |SV−PV| If the deviation is smaller than the gap GP, no operation is performed, and if the deviation is larger than GP, the PID calculation unit 12 performs PID calculation based on the deviation and performs the next operation. Find the amount MV,
This is given to the operating end Pe of the process P to control the process.

The gap changing section 2 then operates as shown in the flowchart of FIG. 2, and gradually reduces the gap over time, allowing for more precise process control. That is, when a gap change operation start command SS is automatically input from an input device such as a man-machine interface or in response to a mode selection signal on the PID control unit 1 side (step S1), first, the gap initial The value GPo is the gap setting value GP
(Step S2). The PID control section 1 side performs PID control based on the gap setting value GP to the gap change section 2.

[0018] Then, this gap setting value GP is PID
When outputted to the control unit 1, the timer 22 starts counting time, and when the preset reduction period t1 has elapsed (steps S3, S4), the timer 22 is reset and the time is changed from the previous gap GP. Subtract ΔGP given as the gap reduction width and convert this to GP'
Then, this GP' is compared with the gap lower limit value GPmin (step S6).

In this comparison, if GP' is larger than the gap lower limit value GPmin, it is possible to change the gap GP to an even smaller value;
' is output to the PID control unit 1 as a new gap setting value GP (step S8). Then, once the new gap setting value GP is output, the timer 22 starts counting the time of the reduction period t1 again, and thereafter, the gap setting value GP is automatically reduced to a smaller value step by step by the reduction width ΔGP every period t1. PID control is performed while changing the

On the other hand, GP' is the gap lower limit value GPmin
If it becomes smaller than (for example, a negative value), it is no longer possible to perform PID control using this GP' as a gap, so instead of GP', PID control is performed using GPmin as the final gap setting value GP. The signal is output to section 1 and PID control is performed (step S7).

[0021] In this way, when setting the gap GP in PID control, by decreasing the gap setting value GP step by step by ΔGP at regular time intervals, a large amount of feedback is initially provided for large deviations. Take control. Then, as the process system gradually stabilizes, the process measurement value PV will no longer fluctuate greatly, so more detailed control is performed, and the process measurement value PV is controlled by effectively tracking the target value SV. be.

Although the above embodiment describes a process control device that automatically changes the gap for PID control, the present invention is not limited to the above embodiment, and can be applied to various processes that perform feedback control. It can be widely applied to control devices.

[0023]

[Effects of the Invention] As described above, according to the present invention, since the gap during feedback control is automatically reduced in stages, large feedback control is initially performed for large deviations. None. As the system gradually stabilizes and the deviation becomes smaller, the gap is changed to a smaller one and feedback control can be performed. This allows effective feedback control from the start of the process until it enters a stable operating state. Moreover, since there is no need to change the gap manually, labor can be saved.

[Brief explanation of the drawing]

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

FIG. 2 is a flowchart showing the operation of the gap changing section of the above embodiment.

[Explanation of symbols]

1...PID control section
11... Deviation comparison section 12... PID calculation section
2... Gap changing section 21... Input/output control section
22...Timer 23...Arithmetic unit
24...Comparison section SS...Start command GP
o... Gap initial value ΔGP... Gap reduction width
t1...Decrease period SV...Process target value
PV...Process measurement value MV...Process operation amount

Claims (1)

[Claims] 1. A process control device that calculates a process manipulated variable based on a deviation between a process target value and a process measured value, and performs feedback control of the process based on the manipulated variable, wherein the process target value and the measured value are a gap setting means for setting a gap with respect to the deviation of the gap, a gap reduction width setting means for setting a gap reduction width for stepwise decreasing the gap set by the gap setting means; A process control device comprising: gap changing means for stepwise decreasing the gap set by the gap setting means by the reduction width set by the gap reduction width setting means.