Fault detection method and device

A fault detection circuit for a programmable logic controller (PLC) system, comprising:

• a detection circuit for detecting a first level of a first detection point disposed before a switch and a load in the PLC system, detecting a second level of a second detection point disposed after the switch and the load in the PLC system, and outputting a corresponding first pulse signal according to a change in the first level and second levels;
• a judgment circuit for judging whether a pulse width of a received first pulse signal is within a permitted range, and outputting a second pulse signal when the judgment result is negative;
• a trigger circuit;
• and
• a display circuit for displaying a detection result in response to a received signal;
• wherein the trigger circuit triggers the display circuit according to a received second pulse signal.

A fault detection method for a programmable logic controller (PLC) system, the method comprising:

• detecting a first level of a first detection point disposed before a switch and a load in the PLC system, detecting a second level of a second detection point disposed after the switch and the load in the PLC system, and outputting a corresponding first pulse signal according to a change in the first and second levels;
• judging whether a received first pulse signal is in a permitted range, and outputting a second pulse signal when the judgment result is negative;
• triggering a display circuit according to the received second pulse signal;
• and
• displaying a detection result in response to a received signal.