JPH0272402A - Wrong output preventing method for digital controller - Google Patents

Abstract

PURPOSE:To prevent the wrong output which is produced when a programmable logic controller PLC is restarted by forcibly keeping the control output in an OFF state for a fixed time of the initial working in the case the abnormality is recovered and an output action is restarted. CONSTITUTION:When a PLC10 detects the abnormality via a self-diagnosing part 26, an R-S flip-flop 70 of a wrong output preventing circuit 60 is reset by the input signal received from the part 26. Thus the circuit 60 controls a contact 44 in an OFF state with the output of the flip-flop 70. The signal to be inputted to an AND element 68 is kept in its previous state for a fixed time by a timer element 66 even though the input signal received from the part 26 is changed at restart after the abnormality is recovered. Therefore no reset input is applied to the flip-flop 70 even with push of a resetting switch 62. Thus the contact 44 is kept OFF. As a result, the wrong output is never produced even with the incomplete recovery of the abnormality.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a digital control device such as a programmable logic controller, and more specifically, digital control at the time of restarting the programmable logic controller after repairing an abnormality. This invention relates to a method for preventing erroneous output from a device.

[Conventional technology]

In general, programmable logic controllers (hereinafter referred to as P
The basic configuration of the LO (referred to as LO) consists of a processor section and an input/output section, and the processor section stores sequence programs in memory to control the machines and equipment to be controlled in a preset fixed order. The input/output section reads input signals from human-powered devices such as limit switches and push buttons, and receives input signals from human-powered devices such as limit switches and push buttons. It functions as an interface that performs mutual conversion between output signals to output devices such as appliances, lamps, and solenoid valves, and signals transferred within the processor section. In addition to this, a power supply section is provided, and since the processor section is composed of a semiconductor circuit, a DC stabilized power supply is used in this power supply section.

The PLO configured in this manner further includes a power supply normality judgment that judges whether a specified power supply voltage is applied, a normality judgment of the arithmetic control section using a watchdog timer, and an input/output check based on a digital input/output car door after light check. It usually has a self-diagnosis function that can determine whether the processing section is normal or not. With this self-diagnosis function, the PLC itself constantly monitors the normal operating status of each part of the PLO, and when an abnormality occurs, the digital control output is forcibly turned off to ensure that the controlled object operates in a safe direction. ,Re-after abnormality repair, ,.

At the time of start, the hardware is reset to release the forced off operation of the digital control output due to the self-diagnosis function and restore the PLC to normal operation.

[Problem to be solved by the invention]

However, according to the PLC described above, there is a possibility that an erroneous output may be output when restarting after repairing an abnormality. In other words, since a restart is performed by performing hardware repairs and also canceling the forced OFF operation of the control output by the PLC's self-diagnosis function, the error repair upon restart was incomplete. In case, PLC
There is a problem in that after the control output starts to be output, an erroneous output is output until the self-diagnosis function detects the occurrence of an abnormality again and the control output is forcibly turned off.

This is because self-diagnosis functions such as the watchdog timer and read-after-light check are functions that can be detected after the PLC has started operating. This is caused by the fact that even if there is an error, it is output as is.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to use a simple configuration to reliably achieve safe control operations that do not cause erroneous outputs when restarting a PLC after an error has been repaired, even if the error is incompletely repaired. An object of the present invention is to provide a method for preventing erroneous output of a digital control device.

[Means to solve the problem]

The method for preventing erroneous output of a digital control device according to the present invention is as follows:
A digital device that is equipped with a digital input/output section and a control calculation section, performs sequence control of the controlled object according to the input program, and has a self-diagnosis function that forcibly turns off the control output to the controlled object when field lightning occurs. In a control device, when the control output is forcibly turned off due to the self-diagnosis function, and then the abnormality is repaired and the output is started again, the control output is forcibly turned off for a certain period of time during initial operation, and after a certain period of time has elapsed. After that, the control output is output to the controlled object by manual input operation using a reset switch.

[Effect]

According to the method for preventing erroneous output of a digital control device according to the present invention, when restarting after an abnormality is repaired, the system is deemed to be abnormal for a certain period of time during initial operation, and the control output of the digital control device is forcibly turned off. do. Thereby, it is possible to prevent erroneous outputs that could occur in the conventional method until the self-diagnosis function is recovered after initial operation. Furthermore, even after a certain period of time has elapsed after initial operation, the control output of the digital control device is not output to the external device unless the reset switch of the external protection circuit is manually turned on, so that abnormality recovery may not be complete. It is possible to reliably prevent erroneous outputs under such conditions.

(Example) Next, an example of the method for preventing erroneous output of a digital control device according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a system diagram of essential parts showing an embodiment of a PLO system equipped with an erroneous output prevention circuit according to the method of the present invention. In FIG. 1, reference numeral 10 is a PLC, and the PLCI
O is composed of a digital input section 12, a processor section 14, and a digital output section 16. The digital input section 12 receives signals from a large number of input contacts 40 through photocouplers 28, and transmits them to the prosenna section 14 in an electrically insulated state. This digital input section 12 also performs a level shift operation to match the external signal level to the signal level of the control calculation section 18 and the like inside the PLC. The processor BIN4 includes a control calculation unit 18 that mainly performs sequential calculation processing according to a sequence program.
, a start section 20 that commands the start of control calculation, a stop section 22 that turns off the control calculation output, and a self-diagnosis section 2.
It consists of 6. The start section 20 and the self-diagnosis section 26 can restart the control calculation and self-diagnosis operation using the reset switch 24. Self-diagnosis section 26
The output signal of is sent to the stop unit 22 and the PLCIO
It should also be sent to the external erroneous output prevention circuit 60.

The digital output unit 16 is composed of a large number of transistors 30 that can directly drive an output relay 42 of a load, a solenoid valve (not shown), etc. based on the output of the control calculation result, and the collector of each transistor 30 is connected to an external positive power source. Connect line P via contact 46 and output relay 42,
The emitter is connected to the ground line or negative power supply line N. Therefore, for the transistor 30 of the digital output section 16, one having a breakdown voltage corresponding to the external power supply voltage is used.

Each output relay 42 is connected to an external device 50 such as equipment or production equipment that is to be controlled by this PLC system.
Controls 0.

The erroneous output prevention circuit 60 has one input as a series circuit of a NOT element 64 and a timer element 66, which receive the signal from the self-diagnosis section 26, and an AND element 68, which receives the signal from the reset switch 62 as the other input. , this AND element 68
An R-S flip-flop 70 which uses the output of
It consists of Then, the on/off operation of the contact 44 is controlled by the output signal of the erroneous output prevention circuit 60.

Next, a method for preventing erroneous output from the PLC system configured as described above will be explained.

First, when the self-diagnosis unit 26 detects an abnormality while PLclo is operating, the self-diagnosis 1 analysis unit 26 sends a signal to the stop unit 22 to force the output of the control calculation result to an OFF state. Work to the side. In addition, the erroneous output prevention circuit 6
0, the R-S flip-flop 70 is in the set state due to the manual signal from the self-diagnosis section 26, so the contact 44 is controlled to be in the off state by the output in response to this.

When the cause of the abnormality is removed and the system is restarted after the abnormality is repaired, the reset switch 24 resets the hardware and starts control calculations. At the same time, the self-diagnosis section 26 also starts operating, but among the self-diagnosis functions, the watchdog timer, door check, etc.
Since these functions can be detected after O operation, the digital control output section 16 may generate an erroneous output until these functions are activated. However, due to the erroneous output prevention circuit 60, even if restarting, the contact 4 remains within a certain period of initial operation.
4, the external device 50 is not controlled due to erroneous output. That is, even if the input signal from the self-diagnosis section 26 to the erroneous output prevention circuit 60 changes at the time of restart, the timer element 66
Since the signal input to the AND element 68 remains in the previous state for a certain period of time, even if the reset switch 62 is pressed, the output of the AND element 68 will not change.
Since the current input to the R-S flip-flop 70 is not performed, the contact 44 can maintain an off state.

When a certain period of time has elapsed after PLO operation, that is, after the time set by timer element 66 has elapsed, the output of AND element 68 to R-S flip-flop 70 will depend on the signal from reset switch 62. . In other words, a state is established in which reset permission is established to enable the input of a cent to the R-S flip-flop 70.

Therefore, if you manually turn on the reset switch 62 of the erroneous output prevention circuit 60 after checking the surrounding situation of the PLC system and confirming that the abnormality has been completely repaired, the R-S flip-flop 70 A reset input is performed, and the output in response turns off the contact 44, which causes the PLC's digital output section 16 to output a production command, etc. to the external device 50, thereby ensuring that erroneous outputs are avoided. can be prevented. Note that it is clear that the fixed time set by the timer element 66 may be set to a time at which self-diagnosis functions such as a watchdog timer and a door after-light check are sufficiently operable.

〔Effect of the invention〕

As is clear from the embodiments described above, according to the present invention,
In a digital control device such as a PLO, by configuring an erroneous output prevention circuit that forcibly turns off the digital control output even if the beam set switch is pressed within a certain period of time during initial operation when restarting after abnormality repair. The abnormality detection time for the self-diagnosis function is ensured, and even if the abnormality repair is incomplete, no control is performed on the external device due to erroneous output during this time. Furthermore, after a certain period of time has elapsed after initial operation, an erroneous output prevention circuit is configured so that operation commands, etc. to external devices are output only by manually turning on the reset switch, so that abnormalities can be completely corrected. The digital control output can be restarted after confirming the above, and erroneous output can be easily and reliably prevented, contributing to improved safety.

Although the preferred embodiments of the present invention have been described above, it goes without saying that various design changes can be made without departing from the spirit of the present invention.

[Brief explanation of the drawings] Figure 1 shows a PLC that implements the method for preventing erroneous output according to the present invention.
It is a system diagram of the main parts of the system. 10. Programmer logic controller (PL)
C) 12, Digital input section 14. ,,processor section 16,,,digital output section 1B,,,control calculation section 2
0,,, Start part 22. ,,stop part 24,,,
Reset switch 26. ,,self-diagnosis section 28,,,photocoupler 30. ,,) transistor 40, ,
, input contact 42. , , output relay 44,
, , Contact 50. ,,external device 60,,
, erroneous output prevention circuit 62, , reset switch 64. ,,NOT element 66,,,timer element 68. ,,AND element 7
0,,,RS flip-flop

Claims (1)

[Claims] (1) Equipped with a digital input/output section and a control calculation section, it performs sequence control of the controlled object according to the input program, and has a self-diagnosis function that forcibly turns off the control output to the controlled object when an abnormality occurs. In a digital control device that has a self-diagnosis function, when the control output is forcibly turned off and then the abnormality is corrected and the output is started again, the control output is forcibly turned off for a certain period of time during initial operation, and the A method for preventing erroneous output of a digital control device, characterized in that after a time has elapsed, a control output is output to a controlled object by manual input operation using a reset switch.