JPS6156522B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital processing type 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 PID (proportional, integral, differential) calculations, etc., but conventionally, the calculations in the processor are based on the ease of manual/automatic bumpless switching, measures to prevent reset/windup, and measures to prevent processor failure. For the ease of
Velocity type calculations were often adopted. However, since velocity type calculation is based on I operation, it is not suitable for performing only P operation or PD operation. Also
Even in the case of PID operation, near the saturation point of the control output, an output pullback phenomenon occurs based on the P and D operations, 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. When performing positional calculations using a digital processor, measures must be taken to prevent manual/automatic bumpless switching and reset/windup prevention.

Furthermore, when performing safety valve control, the control device is required to perform the following operations. Under normal conditions, the process is controlled by another control system, and from the perspective of this control device, the input deviation continues to be excessive. If this condition continues for a long time, the control output will be 100% (or 0%) direction.
When a process becomes abnormal, the measured value from the process exceeds the control point or set point of the controller (which can also be referred to as the upper or lower limit of other control systems) and the deviation changes its polarity. At this moment, the control device starts proportional and integral control of the safety valve.

SUMMARY OF THE INVENTION An object of the present invention is to provide a digital calculation type process control device that performs position type calculations, performs manual-automatic bumpless switching, bumpless switching of proportional gain, and performs safety valve control.

Hereinafter, the present invention will be explained in detail using the drawings.
FIG. 1 is an electrical circuit diagram of the control device of the present invention. In FIG. 1, 1 is a processor (for example, a microprocessor), 21 to 26 are analog comparators provided on the input side, 3 is a digital-to-analog converter (DA converter) provided on the output side, and 4 5 is a semiconductor switch, 5 is an amplifier, 6 is a hold capacitor provided at its input end, 7 is a semiconductor operating switch, and 8 is a manual/automatic changeover switch.

Analog comparators 21, 22, 23, 24, 2
Amplifier 5 is connected to one input terminal of 5 and 26, respectively.
output, measured value Mn of process variable, set value SP,
Proportional gain K _P , integral time T _I , and derivative time T
_D is given as an analog voltage, and the output voltage of the DA converter 3 is commonly given to the other input terminal. These constitute a device for converting an analog input signal into a digital signal and inputting it into the processor 1. That is, the processor 1 sequentially sets the digital output signal to "1" starting from the MSB, and converts this one by one into an analog voltage using the DA converter 3.
This voltage is compared with the respective input voltages in analog comparators 21 to 26, and the logical value of each bit of the digital signal is determined successively in accordance with the comparison output of a desired one analog comparator. The value of the established digital signal is equal to the desired analog comparator input voltage. Analog comparators 21 to 26 are 1
Each time one input signal is taken in, the switching is performed in order, and each input signal is sequentially converted into a digital signal and taken in by the processor 1. Such a configuration has the advantage of eliminating the need for an analog-to-digital converter.

Processor 1 calculates a position-type control output based on the received input signal, and transfers this control output to the DA.
The converter 3 converts the voltage into an analog voltage, and charges the hold capacitor 6 through the semiconductor switch 4. The voltage of capacitor 6 is amplified by amplifier 5,
given to the controlled object. The input impedance of the amplifier 5 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. That is, when the manual operation switch 7 is turned on the + side or the - side, current from a DC constant current source (not shown) flows into or out of the hold capacitor 6, changing the voltage of the 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 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 is bumpless. I can do it.

Now, in the device configured as described above, the calculation of the control output in the processor 1 is performed by the following equation (in the case of PI operation).

y _o =K _P {e _o +△t/T _I Σe _o } (1) Here, y _o ...control output e _o ...deviation △t ...sampling period K _P ...proportional gain T _I ...integration time In other words, processor 1 produces a position type PI control output. In equation (1), if the integral term is I, then
We get the following equation.

y _o =K _P e _o +I (2) In equation (2), the value of I is adjusted as appropriate when switching between manual and automatic switching and when switching proportional gain. When changing the value of I, the value of the integral term is actually changed. Such calculations are performed by a program of the processor 1.

Adjustment of I during manual-automatic switching is performed as follows. When switching from manual control to automatic control, processor 1 uses the manual control output (output of amplifier 5) y _M read just before, proportional gain K _P and deviation e _o to determine the value of I using the following formula. do.

I = y _M - K _P e _o (3) And if the value of equation (3) is set as I of the first control output y _A after automatic switching, y _A = K _P e _o + I = K _P e _o +y _M -K _P e _o =y _M (4) Therefore, no fluctuation in the control output occurs before and after the manual-automatic switching. In other words, switching from manual control to automatic control can be performed bumplessly. Note that switching from automatic control to manual control can be performed bumplessly using capacitor C as described above. Therefore, manual-automatic switching can be performed bumplessly in both directions.

Adjustment of I when switching the proportional gain K _P is performed as follows. When the proportional gain is switched to K _P ', the processor 1 uses the control output y _A read just before, the new proportional gain K _P ', and the deviation e _o to determine the value of I according to the following equation.

I=y _A −K _P ′e _o (5) And the first control output y after proportional gain switching
If we use the value of equation (5) as B of _A ′, y _A ′=K _P ′e _o +I =K _P ′e _o +y _A −K _P ′e _o =y _A (6), and the proportional gain K No fluctuation in control output occurs before and after switching _P. In other words, the proportional gain K _P can be switched bumplessly.

The above calculations are performed by the program of the processor 1, which is shown in a block diagram as shown in FIG. That is, the deviation e _o = SP - Mn is multiplied by K _P , and then the sum of the signal K _P e _o and this signal integrated by the integration register I is passed through a limiter and output as y _o . . During manual to automatic bumpless switching and K _P switching, a switching signal is sent to the integral register I as shown by the dotted line.

Next, the principle of operation of this control device in cases such as safety valve control is shown in a block diagram as shown in FIG. 3. In Figure 3, the deviation e _o = SP - Mn is K _P
It is multiplied and input into integral register I. The integral term (Δ _t /T _I )ΣK _P e _o by the integral register I and the proportional operation term K _P e _o are added and outputted as a control signal via a limiter. Figure 4 shows a time chart for explaining the operation.
represents the relationship between set value SP, measured value Mn, and proportional band. FIG. 4b shows the waveform of the control output y, and FIG. 4c shows the contents of the integral register I. In both cases, the rightward direction of the horizontal axis is taken as time t.
Now, in the normal state when the process is normal, the program of processor 1 switches the switch SW as shown in Figure 3.
is open and the contents of the integral register I are set to the upper limit value H, then the deviation e _o = SP
As long as −Mn is positive, the limiter input has y′=
At H+K _P e _o , the control output y is kept at H.
Now, when the measured value Mn of the process increases and exceeds the set value SP, and an abnormality occurs in the process, the polarity of the deviation e _o is reversed and y'<H, and the control output y deviates from the limit value. is closed by the program of the processor 1, and the proportional/integral control operation starts immediately. In terms of safety valve control, the safety valve changes from a closed state to open according to the control output. Furthermore, when the abnormal state of the process disappears, the measured value decreases, and the deviation e _o increases positively, the calculated output y' reaches the upper limit value H of the limiter, and the control output y becomes Switch SW at the same time as being limited by upper limit value H
is turned off, and the integral register approaches the upper limit value H with a first-order lag as shown by the solid line at a certain time constant, for example, the integration time T _I. The contents of the integral register I at the moment the switch SW is turned off are H−K _P e _o
From now on, it will change in the same direction and reach H. After that, the calculation output y' = H + K _P e _o , so the control output y
=H is maintained.

Note that the limiter also operates on the lower limit value L, and in the above example, the lower limit value L corresponds to the state where the safety valve is fully open.

In the above description, an example of a processor that saves analog/digital converters has been given, but the processor may have a general configuration using an analog/digital converter and digital/analog conversion as shown in FIG. 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 explained above, according to the present invention, manual-automatic bumpless switching and proportional gain bumpless switching can be performed using position type calculations, and safety valve control can be performed stably without impacting the process. A digital calculation type process control device can be realized.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram showing one embodiment of the process control device according to the present invention, FIGS. 2 and 3 are block diagrams for explaining the operating principle of the device of the present invention, and FIG. 4 is for explaining the operation. time chart,
FIG. 5 is an electrical circuit diagram showing another embodiment of the device of the present invention. 1...Microprocessor, 21, 21, ~2
6...Analog comparator, 3...Digital/analog converter, 4...Semiconductor switch, 5...Amplifier, 6...Hold capacitor, 7...Semiconductor operation switch, 8...Manual-automatic changeover switch.

Claims (1)

[Claims] 1. A processor, comprising a signal reading means for reading at least a measured value, a set value, and a proportional gain into the processor, and the processor reads the measured value and the set value via the signal reading means. At the same time, the deviation signal between the measured value and the set value is subjected to at least proportional and integral calculations using position type calculations to obtain the automatic control output, and when the automatic control output exceeds a predetermined limit value, the integral operation is performed. is stopped, the integral term is made to match the limit value with a delay of a predetermined time constant, and when the proportional gain is switched, the control output Y _A and the new proportional gain after switching are
A process control device that resets the value of an integral term I according to the following equation using K' _p and deviation e _o . I=Y _A −K′ _p e _o .