JPH0239202A - Process control circuit - Google Patents

Abstract

PURPOSE:To avoid deterioration of the control result despite deterioration of the load for a process control circuit which includes the proportion, integration and differentiation elements by adding a division circuit to the input side to divide the input by the load applied to a process or the manipulated variable. CONSTITUTION:A PID control circuit controls the process of an integral element 2 including an equivalent dead time element 1 via a PID controller 7. This controller 7 includes a proportion element 4, an integration element 5 and a differentiation element 6. At the same time, a division circuit 8 is set at the input side of the element 4. The control deviation between the target value (r) and the controlled variable (x) is inputted to the circuit 8 together with the manipulated variable (m). The circuit 8 has a function to divide the control deviation (r-x) by the variable (m). In such a constitution, the deviation of the variable (x) is gradually reduced as the load is deteriorated. In other words, the control result is improved with deterioration of the load.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to a process control circuit, mainly a PTD control circuit for an integral process including dead time or a first-order lag process including dead time.

(b) Conventional technology For example, in an integral process that includes dead time, as shown in FIG. 3, an IID adjustment 237 consisting of a proportional (P) element 4, an integral (1) element 5, and a differential (D) element 6 is used to control the control amount χ to the target value r. In this process 3, conventionally, when the control meter X deviates from the target value r due to a change in the load V applied to the process, the control meter
In order to control the PID controller 7, each control parameter of the PID controller 7 is set to the value proposed by Ziegler-Nichols (proportional gain: 1.
2T/L, integral time: 2■2, differential time: L/2). This Ziegler-Nichols value is determined so that the optimum control result can be obtained when the load applied to the process is at the rated value (100%).

(c) Problems to be Solved by the Invention With the conventional system that uses the Ziegler-Nichols value described above, when the load is 100%, optimal control results can be obtained, so there is no problem, but when the load V applied to the process As the load decreases, the integral time constant 〒 and the dead time r of the process characteristics increase, so that as the load decreases, the response of the control result gradually becomes oscillatory, as shown in FIG. The example in FIG. 5 shows the integral time constant T of the process at rated
= 4.75 minutes, dead time I = 2.24 minutes, and these are the calculation results when the load decreases by 20% from 100% to 20%. The response curve at 100% is 10 minutes,
The deviation is 0 at 20 minutes and 30 minutes.

As described above, the conventional control circuit has a problem in that the control result deteriorates as the load decreases.

The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a process control circuit that does not deteriorate the control results even when the load decreases, but rather improves the control results.

(d) Means and operation for solving the problem The process control circuit of the present invention includes a proportional element, an integral element, and a differential element, and divides the input by the load applied to the process or the manipulated variable on the input side. It features a dividing circuit.

In this process control circuit, when the load decreases, for example, as shown in FIG. 3, as the load decreases, the vibration of the response characteristic becomes smaller and the control result becomes better.

(E) Examples The present invention will be explained in more detail with reference to Examples below.

FIG. 1 is a block diagram of a PID control circuit showing one embodiment of the present invention. This PrD system f711 @ path also converts process 3 of integral element 2 containing equivalent dead time element l to P
It is adjusted by an ID regulator 7, and the PID regulator 7 includes a proportional element 4, an integral element 5, and a differential element 6.

In this respect, it is similar to the conventional PID control circuit shown in FIG.

A feature of the PID control circuit of this embodiment is that a division circuit 8 is provided on the input side of the proportional element 40.

This division circuit 8 has the input of the PrD control circuit, that is,
The target value r−control deviation of the control amount X is input, and
The output of the PID regulator 7, that is, the operation 4itm is added. This dividing 1γ circuit 8 has a function of dividing the control deviation r−x by the manipulated variable m.

In this PID control circuit, the Ziegler-Nichols PID parameters are set for a process with the same characteristics as the circuit in Figure 4, that is, for the rated integral time constant T = 4.75 minutes and dead time L = 2.24 minutes. Then, the load V is increased from 100% to 2
When it decreased by 20% to 0%, the calculation result became as shown in FIG. Looking at the response characteristics in Figure 3, the response curves for 9.100% load are 10 minutes, 20 minutes, and 30 minutes.
The deviation becomes 0 in minutes, which is the same as in Figure 5, but is there a limit? I@x
As the load force decreases, the deviation becomes 11111 times smaller. In other words, as the load decreases, the control results actually become better.

In addition, on the T flow side of H, the control deviation r-X is divided by 1 m of operation, but 1 m of operation is always equal to load V.
Since the control circuit is working, the operation tim can be considered to be a load ■. Therefore, if the load V is known, that is, it is known, the load V
A similar result can be obtained by adding the control deviation rx to the division circuit 8 and dividing the control deviation rx by the load V. In the PTD control circuit shown in FIG. 2, except for the circuit that divides the control deviation r-x by the manipulated variable m, the other circuit parts are the same as the PID control circuit shown in FIG. 1.

(f) Effects of the Invention According to the present invention, by providing a division tγ circuit that divides the input of the regulator by the output (tW operation @), as the load on the process decreases, the control result of the controlled variable becomes worse. It is possible to eliminate the conventional drawbacks of 1I and obtain better control results as the load decreases.
The example of using Ziegler-Nichols control parameters for an integral process involving an iIF interval is of course applicable to any process control system.

[Brief Description of the Drawings] Fig. 1 is a block diagram of a PrD control circuit showing one embodiment of the present invention, and Fig. 2 is a block diagram of a PrD control circuit showing another embodiment of the invention.
A block diagram of the IDffI control circuit, FIG. 3 is a diagram showing an example of the response characteristics of the PID control circuit of the above embodiment, FIG. 4 is a block diagram showing a conventional P r D i I + control circuit,
FIG. 5 is a diagram showing an example of response characteristics of a conventional PIDfflII control circuit. 3: Process, 4: Proportional element, 5: Integral element, 6: Differential element, 7: PrD controller, 8: Divide circuit, m: Manipulated amount, X: Controlled amount, r: Target value, ■= Negative load

Claims (1)

[Claims] (1) A process control circuit including a proportional element, an integral element, and a differential element, characterized in that the input side is provided with a divider circuit that divides the input by the load applied to the process or the manipulated variable.