JPH0119162B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device, and more particularly to improving the reliability of a control device in manual operation, which has an automatic-manual mode switching device whose arithmetic unit is configured digitally using a microprocessor.

Microprocessors are now being used in modern control devices, which have the advantage of allowing highly accurate control with no drift compared to conventional analog control devices, and improving controllability through software. Not only is it highly economical, it also facilitates man-machine communication with operators.
Since it is easy to maintain, it is being applied to control in a wide range of fields.

FIG. 1 shows a conventional example of such a control device, and here, an example in which it is applied to level control of a tank will be described below.

In the figure, 1 is the control station;
2 is a digital control device, 3 is a flow control valve, and 4 is a tank.

The control station 1 includes a two-needle meter 11 having a pointer 11A indicating the command value a and a pointer 11B indicating the actual process amount b, an automatic mode selection push button (hereinafter abbreviated as automatic PB) 12A, and an automatic mode command. Value increase push button (hereinafter abbreviated as command increase PB) 12B, automatic mode command value decrease push button (hereinafter abbreviated as command decrease PB) 12C, manual mode selection push button (hereinafter abbreviated as manual PB) 13A, manual mode Command value increase push button (hereinafter abbreviated as manual increase PB) 13B,
A manual mode command value reduction push button (hereinafter abbreviated as manual reduction PB) 13C is provided.

The digital control device 2 includes an adder circuit 21 that calculates the deviation c between the command value a from the control station 1 and the actual process amount b representing the level l of the tank 4, and a microprocessor configured calculation circuit that calculates the deviation c by PID. It consists of a circuit 22, a counter 23 that holds its output signal d and increases or decreases its value based on manual commands from the control station 1 when in manual mode, and a D/A converter 24 that converts its output e into an analog quantity f. ing.

Control station 1 automatic PB12A
When pressed, contact X closes and contact Y opens. Conversely, when manual PB13A is pressed, contact X opens and contact Y closes.

Now, an almost constant amount of water ΔQ is constantly flowing into the tank 4, and the tank water level l is to be controlled to a predetermined water level based on commands from the control station 1. If this is to be done in automatic mode, first, Press automatic PB12A, then increase command PB12 while looking at pointer 11A of meter 11.
B or operate command decrease PB12C. As a result, the command value a is added to the addition circuit 21 of the digital control device 2, the deviation c from the actual process amount b is subjected to PID calculation by the calculation circuit 22, and since the contact X is closed, the signal d is sent to the counter 23. Retained. The output e is converted into an analog signal f by the D/A converter 24 and applied to the control valve 3.

This analog signal f generally has a value of about 4 to 20 mA, and the control valve 3 is maintained at an opening proportional to this value, and the outflow amount Δq is adjusted.

In this way, the tank water level l is controlled according to the command value a, and its actual value is displayed on the meter 11 by the pointer 11B. Therefore, in a steady state, the pointers 11A and 11B on the meter 11 match.

If you want to switch to manual mode from this state,
Press manual PB13A. Then, the mode switching signal g causes the contact X to open and the contact Y to close, so that the arithmetic circuit 22 is disconnected from the counter 23, and the value of the counter 23 is placed under manual control as the contact is closed. At this time, since the counter 23 holds the output d of the arithmetic circuit 22 immediately before the switching, the switching is performed without a shock. Next, manually increase PB13B or manually decrease PB13C
, the value of the counter 23 is gradually changed in accordance with the command pulse h.

Further, when returning to the automatic mode again, switching is performed bumplessly in the same manner as described above.

In this way, by configuring the control device using a microprocessor, the configuration becomes extremely simple.In the example above, we explained simple level control, but by simply changing the internal software, it is possible to control a thermal power plant. It can be applied to various complex controls such as automatic control, and automatic-manual switching control can be performed extremely well while maintaining man-machine communication with operators.

However, in the control device having the above-mentioned conventional configuration, if the digital control device 2 fails, manual control becomes impossible, and there is a risk that the control system will run out of control.

In other words, in order to ensure the safety of the control system no matter what part of the control device malfunctions, in the event that automatic control becomes impossible, manual control is the only option available as a last backup method. I have to keep it. However, the conventional configuration described above has a drawback that, for example, if the counter 23 breaks down, neither automatic control nor manual control is possible.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a highly reliable control device that eliminates the drawbacks of the conventional devices described above and ensures manual control as the final backup means.

In order to achieve this objective, the present invention provides a diagnostic device to constantly diagnose the manual control circuit during automatic control, and if a malfunction in the manual control circuit is discovered during that time, the manual control circuit can be controlled while performing automatic control. The feature is that the circuit can be repaired.

Hereinafter, the present invention will be explained with reference to the embodiments shown in the figures.

FIG. 2 shows a configuration diagram of a control device according to an embodiment of the present invention, and the same reference numerals as in FIG. 1 indicate the same or corresponding parts. The difference in the configuration of the figure from that of FIG. 1 is that the counter 23 is omitted and an analog memory 25 is connected to the output side of the D/A converter 24 instead, and the output f of the D/A converter 24 is connected during automatic control. The signal is output to the control valve 3 through the switching device 26, in which tw is conductive in automatic mode and s-w is conductive in manual mode, and the value of analog memory 25 is stored while the signal is held in analog memory 25. Diagnosis is performed by feeding back to the diagnostic device 27 of the digital control device and monitoring the deviation between the PID calculation result and the output signal i, and if an abnormality occurs, it is output to the alarm device 28.

That is, as in the case of FIG. 1, during automatic control, the deviation c between the command value a and the process amount b is subjected to PID calculation in the calculation circuit 22, and the output d is immediately converted to the analog signal f by the D/A converter 24. converted to
The signal is applied to the control valve 3 via t-w of the switching device 26, and the control valve 3 is adjusted to an opening degree according to the analog signal f. Thereby, the water level l of the tank 4 is controlled according to the command value.

At this time, the analog memory 25 holds the analog signal f and outputs it to the diagnostic device 27. The diagnostic device 27 converts this analog signal back into the original digital signal, and determines whether the analog memory 25 is normal or abnormal by checking the coincidence with d output from the arithmetic circuit 22. As a result, if the output of the analog memory 25 and the output of the arithmetic circuit 22 do not match, the analog memory 25 detects an abnormality and activates the alarm device 28 to notify the operator. This allows the operator to replace or repair the analog memory 25 while on-line, that is, with the control device operating in automatic mode. Therefore, the analog memory 25 can always be maintained in a normal state, and besides the analog memory 25, the only components of the manual circuit are the manual operation circuit of the control station 1 and the switching device 26, which are the original components. The highly reliable circuit design ensures that even in the worst case, only the manual control circuit is available.

Next, when switching from automatic mode to manual mode, the arithmetic circuit 22
The input c of the analog memory 25 and the input f of the analog memory 25 are disconnected, and the switching device 26 is switched. At this time, since the analog memory 25 holds the analog signal f immediately before the switching, the switching is performed without any trouble. Next, as above, manually increase the
A corresponding command pulse h is added to the analog memory 25 in response to the operation of the PB13B or manual reduction PB13C. The analog memory 25 increases or decreases the analog value held therein by a predetermined amount in response to the command pulse h. The analog signal i is applied to the control valve 3 via the switching device 26, thereby adjusting the opening degree of the control valve 3 and manually controlling the tank water level l.

At this time, the output i of the analog memory 25 is converted into a digital signal and input to the arithmetic circuit 22 via the diagnostic device 27. As mentioned above, since the arithmetic circuit 22 is configured as a microprocessor, the output d is always outputted from the internal memory. Therefore, the value in this memory is the diagnostic device 27.
is replaced by the digital value input via the . As a result, the output f of the D/A converter 24 is made equal to the output i of the analog memory 25 in the manual mode.

As a result, when switching to the automatic mode again, the memory of the arithmetic circuit 22 that outputs the signal d also gradually changes its value according to the PID calculation result of the input deviation c, so there is no shock in this case as well. The switch is made to

In this way, automatic-manual mode switching is performed bumplessly, and abnormalities are detected while constantly diagnosing the analog memory 25 during automatic mode selection, so the manual circuit is reliably secured and automatic control is performed. Even in the worst case scenario, manual control becomes possible and the control system can be operated safely.

As described above, according to the present invention, it is possible to obtain a highly reliable control device that can ensure only manual control as the last backup means.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional control device, and FIG. 2 is a block diagram of a control device showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Control station, 2...Digital control device, 3...Flow control valve, 4...Tank, 11...Meter, 11A, 11B...Pointer,
12A...Auto mode selection push button, 12B...Auto mode command value increase button, 12C...Auto mode command value decrease push button, 13A...Manual mode selection push button, 13
B...Manual mode command value increase push button, 13C...Manual mode command value decrease push button, 21...Addition circuit, 22...
...Arithmetic circuit, 23...Counter, 24...A/D
converter, 25... analog memory, 26... switching device, 27... diagnostic device, 28... alarm device.

Claims (1)

[Claims] 1. In a control device that is equipped with an automatic-manual mode switching device, and in the automatic mode, the control deviation is compensated for and the control target is controlled using the result, while in the manual mode, the controlled target is directly controlled by manual operation commands. outputs a compensation calculation for the control deviation between the command value and the actual value, while in manual mode it has an arithmetic circuit that outputs a manual operation command, and in automatic mode it stores the output of the arithmetic circuit; memory means for storing manual operation commands; and automatic mode at the output of the arithmetic circuit;
The manual mode includes a switching device that switches the output of the memory means and adds it to the controlled object, a diagnostic device that compares the output of the memory means and the output of the arithmetic circuit to determine whether the memory means is normal or abnormal, and this diagnosis. When the device detects an abnormality in the memory means,
A control device comprising: an alarm device that outputs an alarm to the outside.