JPS5875209A - Process controller - Google Patents

Abstract

PURPOSE:To prevent the fluctuation of an automatic control output, by performing process control for a position type operation and setting again the value of the integral arithmetic term when the proportional gain is changed. CONSTITUTION:A processor 1 sets successively the digital output signals at ''1'' and after MSB and then converts them into an analog voltage. This analog voltage is compared with the input voltage through analog comparators 21-26 to obtain digital signals. The processor 1 calculates a position type control output in response to the fetched data, the proportional gain and the integrating time and converts the control output into the analog voltage to charge it to a holding capacitor 6. An automatic operation is switched in a bumpless way by varying manually the voltage of the capacitor 6. Furthermore, the proportional gain is switched in a bumpless way by calculating and setting again the new integrating term when the proportional gain is switched.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital process control device.

A digital arithmetic type process control device is constructed using the arithmetic functions of a computer or a microprocessor (hereinafter simply referred to as a processor). The processor determines the control output by performing PI'D (proportional, integral, differential) calculations, etc., but conventionally, the calculations in the processor are based on the ease of manual/automatic bumpless switching, reset/windup prevention measures, and the processor Speed type calculations were often adopted because of the ease of troubleshooting. However, since velocity type calculation is based on a machining operation, it is not suitable for performing only a P operation or a PD operation. Further, even in the case of PID operation, an output pullback phenomenon occurs due to P and D operations near the saturation point of the control output, which is disadvantageous.

A position type calculation process control device is considered to be suitable for P operation and PD operation and does not cause the output pullback phenomenon.

Here, the present invention configures a device using a processor that performs digital calculations, and even if a proportional band (proportional gain) is set in a state where there is a deviation,
This book attempts to provide a device that does not cause fluctuations in automatic control output.

One feature of the present invention is that at least a PI operation is performed by position type calculation, and the value of the integral calculation term is reset when the proportional gain Kp is changed.

The present invention will be explained below with reference to the drawings. FIG. 1 is a conceptual block diagram of an embodiment of the present invention. In FIG. 1, 1 is a processor (for example, a microprocessor), 21 to 26 are analog comparators provided on its input side, and 3 is a digital-to-analog converter (DA converter) provided on its output side.
4 is a semiconductor switch, 5 is an amplifier, 6 is a capacitor provided at the input end of the amplifier 5, 7 is a manually operated switch, and 8 is a manual/automatic changeover switch.

Analog comparator 2: L, 22.23.24.25.2
The output of the amplifier 5, the process variable T□, and the differential time TD are respectively given as analog voltages to one input terminal of the converter 6, and the output voltage of the DA converter 3 is commonly given to the other input terminal. These are Ana! A mechanism for converting a digital input signal into a digital signal and inputting it into the processor 1 is configured. That is, the processor 1 sequentially rIJKs the digital output signal y2 starting from the MSB, converts it one by one into an analog voltage using the DA converter 3, compares this voltage with each input voltage in the analog comparators 21 to 26, and obtains the desired signal. The logical value of each bit of the digital signal is determined successively in accordance with the comparison output of one analog comparator.

The value of the established digital signal is equal to the desired analog comparator input voltage. The analog comparators 21 to 26 are switched in order every time the MB input of one input signal is completed, and each input signal is sequentially converted into a digital signal and taken into the processor 1. Such a configuration also has the advantage of eliminating the need for an analog-to-digital converter.

The processor 1 takes in the measured value Mn, the set value sp,
1 Calculate the position type control output based on each input signal such as proportional gain Kp, integral time T, differential time, etc.
This control output is converted into an analog voltage by the DA converter 3,
A hold capacitor 6 is charged through a semiconductor switch 4. The voltage of the capacitor 6 is amplified by the amplifier 5 and applied to the controlled object. The input impedance of the amplifier 50 is set sufficiently high so that attenuation of the charge on the hold capacitor 6 does not become a problem.

The acquisition of input signals and the calculation of control outputs are repeated at a constant sampling period. The sampling period is set to about 0.1 sec, for example.

The voltage of the hold capacitor 6 can be increased or decreased as desired by the operator during manual control.

In other words, when the manual operation switch 7 is turned to the + side or one side, the current from the DC constant current source (circuit) is held or
It flows into or out of capacitor 6 to change the voltage of hold capacitor 6. Therefore, this allows manual control of the controlled object. When switching to manual control, the latest value of the control output of the processor 1 is held in the hold capacitor 6, and manual control can be started using that value as a starting point, so switching from automatic control to manual control can be done at the pan press. I can do it.

Now, in the device configured as described above, the calculation of the control output in the processor 1 is performed using the following formula (P
In case of I operation).

Here, y... Control output e... Deviation Δt... Sampling period Kp... Proportional gain T... Integral time, that is, the processor 1 generates a position-type PI control output. In equation (1), if the integral term is B, the following equation is obtained.

y = Kpe + B (2
)n n Here, if the proportional gain Kp is changed to Kl)+, (2
), the proportional term Kp −e becomes Kl)r·e, so n n If this continues, the control output y will fluctuate, which is undesirable.

n Therefore, in this device t, the processor 1 performs the following operation to reset the value of the integral term B when changing the proportional gain Kp.

That is, when the proportional gain is switched to Kpl, the processor 1 uses the control output yA read immediately before, the new proportional gain Kpl, and the deviation e- to determine the value of the integral term B according to equation (3).

””A-Kp”n (
3) When the value of the integral term B is reset according to equation (3), the initial control output yA' after switching the proportional gain becomes as shown in equation (4), and the fluctuation of the control output before and after switching the proportional gain Kp does not occur. That is, the proportional gain Kp can be switched bumplessly.

yAIwKpIen+B m Kp'en+ yA-Kp'en 口yA (4) Such calculations are performed by the program of the processor 1, and for convenience of explanation, they are shown in a conceptual diagram as shown in FIG. Moreover, 70 charts of the above (y) q> operations can be shown in FIG.

In addition, in FIG. 3 70-, other operations 74- such as manual-automatic switching are omitted. The explanation according to this flow is as follows.

(1) After turning on the power, control the flow. Let's initialize the flags.

(2) Sense the sampling period.

(3) Measured value Mn, set value sp, output value 7. P.I.D.
Performs A/D conversion of a constant and stores the result in an internal memory.

(4) Check whether the proportional gain Kp has been changed.

(5) If there is no change in Kp, perform the PI (D) calculation as shown in equation (1).

(6) Output the calculation results.

(7) In step (4), if there is a change in Kp, the integral term B is calculated using equation (3), and the result of this calculation is reset to the integral term B in equation (1).

(8) Next cycle niote, IKpI-Kpl-Oo
In the case (when there is no change in Kp'), in step (5), a PI(D) calculation is performed using the integral term Btl reset in step (7) as its initial value. The same applies thereafter.

As is clear from the above flow, when changing the proportional gain Kp, the change can be performed bumplessly by steps (4) and (7).

In the above explanation, we have given an example of a processor that saves analog/digital converters, but as shown in Fig. It may be a composition. Furthermore, although the example of a single-loop controller has been given, the present invention can also be applied to a device that controls multiple loops.

As described above, in the present invention, the processor is used to pressure the processor to perform at least 4Pr operation by position type calculation, and the value of the integral calculation term is reset when the proportional gain is changed. Therefore, according to the present invention, it is possible to obtain a digital calculation type process control device that takes advantage of the position type calculation and can effectively perform bumpless switching of the proportional gain. Therefore, the device according to the present invention is effective when the proportional gain (8) is set by an external combinator or the like.

[Brief explanation of drawings]

Fig. 1 is a conceptual block diagram of an embodiment of the present invention, Fig. 2 is a conceptual diagram of calculation, Fig. 3 is a flowchart showing the flow of operation, and Fig. 4 is a conceptual block diagram of another embodiment of the present invention. It is. DESCRIPTION OF SYMBOLS 1... Processor, 21-26... Analog comparator, 3... Digital-to-analog converter, 4... Semiconductor switch, 5... Amplifier, 6... Capacitor, 7
...Manual operation switch, 8...A/M changeover switch.

Claims (1)

[Claims] (1) A processor, comprising a signal reading means for reading at least a measured value, a set value, a proportional gain Kp, and an integral time TIt into the processor;
Proportional gain Kp j read in every sampling period Δ weight through the signal reading means by integral calculation, deviation e between the measured value and set value, and integration time T1 When changing the automatic control output example gain xp, the automatic side (Foundation) Output YA, new proportional gain Kp+ and deviation en
A process control device characterized in that it performs an operation of resetting the device so that it can be viewed. B″YA-Kp'en