1. What are the types of PLC failures?
External device failure
External devices are various switches, sensors, actuators, loads, etc., that directly interact with the PLC's operational processes. Failures in these devices will directly affect the control functions of the PLC system. Therefore, when repairing a PLC, the first step is to determine whether the fault lies with an external device or the PLC itself.
System failure
1) System failure is a global failure that affects the operation of the PLC system.
2) PLC system faults can be divided into fixed faults and random faults.
3) If the system can be restarted to restore normal operation after a fault occurs, it is considered an intermittent fault. If restarting fails to restore normal operation and requires hardware or software replacement, it is considered a persistent fault.
Hardware failure
PLC hardware failures mainly refer to failures caused by damage to modules or circuits in the PLC system.
Software malfunction
PLC software faults include software errors and operational errors. PLC software faults can generally be checked and examined through the PLC's own self-diagnostic testing function or software.
2. What is the failure rate of the PLC control system?
1) The CPU and memory failure rate is 5%.
2) The failure rate of I/O modules is 15%.
3) Sensor and switch failure rate is 45%.
4) The actuator failure rate is 30%.
5) Failure rates related to wiring and other aspects account for 5%.
3. What are the common sources of PLC failures?
1) Relays and contactors.
2) Valves and gates.
3) Some components or equipment for switches, limit positions, safety maintenance, and on-site operation.
4) Sub-devices in the PLC system.
5) Sensors and appearance.
6) Noise from power supply, ground wires, and signal lines.
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