Clever Judgment of PLC Trouble in Web Offset Press

A P40 rotary offset printing machine made in Shanghai in the factory, once powered on, appeared a fault in the programmable controller (PLC) part of the electric box without any indication, all the external displays of the whole machine were none, and the operation was invalid.

The PLC of this machine adopts the FX2N-4DA type programmer made by Mitsubishi of Japan. The PLC220V power supply voltage (L and N terminals) is measured first, and the value is normal. Then open the PLC to see if the internal insurance is burned out, and the insurance is intact. Because there is no PLC details, it is impossible to determine whether there is a problem with the PLC internal circuit or the peripheral circuit.

Since the peripheral circuits and the main electrical box are all plug-connected, the operator adopts the elimination method to disconnect all peripheral circuits (aviation plugs P1, P2A, P3A) except the main motor in the electrical box, and then connect the debug board to connect Transfer the switch to the debug file. After the power-on test, the whole machine returned to normal, indicating that the PLC is intact, so it is judged that the fault is in the peripheral circuit connected to the three plugs. Then switch the transfer switch to the operating gear, and then plug in P3A, P2A, P1 and power on the test respectively. As a result, when P1 is connected, the PLC indication is none. After careful inspection of this part, it is found that the IN24 line is exposed to ground. Wrap the exposed joints and power on for commissioning. The fault is eliminated and normal.

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