JPS6389901A - Control circuit for programmable controller - Google Patents

Abstract

PURPOSE:To continue or stop an operation even at the time of abnormality by providing a logic circuit that detects abnormality of a programmable controller by an external equipment and outputs a signal to operate the plant/process to safety side. CONSTITUTION:A monitoring device 5 monitors output signals of a programmable controller (PC) 1, and detects abnormality of PC 1 from periodicity and regularity of the signals. A logic circuit 6 consists of an AND gate that makes the output of DFF 2 and the output of the unit 5 input, an inverter 8 that inverts the output of the unit 5 and an OR gate 9 that makes these output input. The unit 5 detects abnormality of PC 1 by periodicity and regularity of data and strobe signals, and blocks control signals from DFF 2 in the circuit 6. The signals of low level outputted from the unit 5 is inverted by the inverter 8 and becomes '1', and outputted to the plant/process 4 through the OR gate 9 as a signal that holds and controls it to safety side.

Description

Detailed Description of the Invention [Industrial Field of Application] This invention provides a method for controlling a plant/process when a programmable controller is used as a plant control device, and when an abnormality occurs in the programmable controller. This invention relates to a control circuit for a programmable controller that controls safely.

[Conventional technology]

Figure 3 is a block diagram showing the output method of a conventional programmable controller, as described in, for example, "Input/Output Control and System Configuration" (published by Ohsha, March 20, 1980). , 1 is a programmable controller (hereinafter referred to as PC) that performs logical operations and is used as a computer, and 2 is a D flip-flop. In addition, the above P
The CI outputs data corresponding to the control command to the data output of the D flip-flop 2, and outputs a strobe pulse δ to the clock output C of the D flip-flop 2.

FIG. 4 shows the relationship between the above-mentioned PCI, D-flip flop 2 and external systems, where 3 represents an operation control panel and 4 represents a plant/process.

Next, the operation will be explained. Signals from the operating control panel 3, together with signals from the plant/process 4, are input to the PCI and output to the D flip-flop 2 according to logic preprogrammed within the PCI. D
The flip-flop 2 identifies the value of the data to be output based on the data, which is a binary control command, and the time of transition of the step, and sends a control signal to the plant/process 4.

[Problem that the invention seeks to solve]

Since the conventional PC control circuit is configured as described above, it does not detect an abnormality in the PCI itself, so it is not possible to prevent erroneous output from the PCI in the event of a PCI abnormality. The incorrect output from the PCI will cause auxiliary equipment and valves to malfunction, affecting the plant/process 4, so it is necessary for the operator to manually disconnect the PCI before repairing the plant/process 4. There were some problems.

This invention was made in order to solve the above-mentioned problems. It detects when a PC is abnormal, and allows the plant/process to operate in a safe manner, thereby preventing any adverse effects on the plant/process. The object of the present invention is to obtain a control circuit for a programmable controller that can continue operation without causing any adverse effects.

[Means for solving problems]

The control circuit of the programmable controller according to the present invention includes a monitoring device that monitors the output of the PC and detects an abnormality of the PC6, and outputs a signal from the logic circuit to safely control the plant/process when an abnormality occurs. It is composed of

[For production]

The monitoring device in this invention detects abnormalities in a PC.
is detected from the periodicity and regularity of the output signal, and when this abnormality is detected, a logic circuit blocks the output of the D flip-flop and outputs a signal to the plant/process that causes the plant/process to operate on the safe side. It acts like this.

〔Example〕

An embodiment of the present invention will be briefly described below with reference to the drawings. 1st
In the figure, 5 is a monitoring device, which monitors the output signal of the programmable controller 1, and based on the periodicity and regularity of this output signal, the programmable controller 1
Detects abnormalities. 6 is a logic circuit which receives the output of the D flip-flop 2 and the output of the monitoring device 5;
It consists of an ND gate 7, an inverter 8 that inverts the output of the monitoring device 5, and an OR gate 9 whose inputs are the output of the AND gate 7 and the output of the inverter 8.

Next, the operation will be explained.

The signal from the PCI is output to the D flip-flop 2 and the monitoring device 5, but the monitoring device 5 detects abnormalities in the PCI due to the periodicity and regularity of the data and strobe signals.
If the PCI is abnormal, the control signal from the D flip-flop 2 is blocked by the four-sic circuit 6. In other words, the monitoring device 5 outputs a low level signal "01" at the time of the above abnormality, and the output of the AND gate 7 is set to 101.
and block output to plant/process 4. On the other hand, the low level signal output by the monitoring device 5 is inverted by the inverter 8 and becomes 111, and sent to the plant/process 4 via the OR gate 9 on the safe side (maintaining the state immediately before the abnormality occurs). , valve open/close) as a control signal. 2 shows an example in which the plant/process 4 is turned off to keep the plant/process 4 on the safe side (pump stopped) in the event of the above abnormality. Here, the logic circuit 6 inputs each output of the D flip-flop 2 and the monitoring device 5. AND
It consists of only gate 7. According to this, when the monitoring device 5 detects the above abnormality, the low level signal W
Since □I is output, the output of the AND gate 7 is also wl, and the operation of the plant/process 4 is stopped.

〔Effect of the invention〕

As described above, according to the present invention, when the PC is abnormal, the output of the D flip-flop is blocked and the plant/process is switched to the safe side. Since the structure is equipped with a logic circuit that outputs a signal to operate the plant/process, it is possible to continue operation or stop the operation without adversely affecting the plant/process. effective.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a control circuit of a programmable controller according to an embodiment of the present invention, FIG. 2 is a block diagram showing another embodiment, and FIG. 3 is a block diagram showing a control circuit of a conventional programmable controller. FIG. 4 is a block diagram showing the overall configuration of the control circuit of FIG. 3 and an external system. 1 is a programmable controller (PC), 2 is a D flip-flop, 4 is a plant/process, 5 is a monitoring device, 6 is a logic circuit, 7 is an AND gate, 8 is an inverter, and 9 is an OR gate. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.
, Patent applicant Mitsubishi Electric Corporation Figure 1 Figure 2 et al.

Claims (3)

[Claims] (1) In a programmable controller control circuit that includes a programmable controller that performs logical operations upon receiving operation commands from an operation control panel, and a D flip-flop that latches binary control commands based on the calculation results of this programmable controller, a monitoring device that visually observes the output signal from the programmable controller and detects an abnormality in the programmable controller based on the periodicity and regularity of the output signal; and blocking the output of the D flip-flop when the monitoring device detects an abnormality. What is claimed is: 1. A control circuit for a programmable controller, comprising: a logic circuit for outputting a signal for safely controlling a plant/process; (2) A control circuit for a programmable controller according to claim 1, wherein the logic circuit is an AND gate whose inputs are each output of a D flip-flop and a monitoring device. (3) The logic circuit is an AND gate whose inputs are each output of the D flip-flop and the monitoring device, and this AND gate.
2. A control circuit for a programmable controller according to claim 1, comprising an OR gate whose inputs are an output of the gate and an output obtained by inverting the output of the monitoring device.