A safety circuit is an interlocking control circuit used to protect loads or control objects and prevent operational errors or control failures. While directly controlling the load, the safety protection circuit inputs signals to the PLC to prevent PLC protection processing from being compromised. Safety circuits generally consider the following aspects. H4135A-99-2413560 HIMA Safety Relay (1) Short circuit protection should be installed in the external output circuit fuse of the PLC for short circuit protection. It is best to place a fuse in the circuit of each load. (2) Interlocking and interlocking measures: In addition to ensuring the interlocking relationship of the circuits in the program, the external wiring of the PLC should also adopt hardware interlocking measures to ensure the safe and reliable operation of the system. (3) Voltage interruption protection and emergency shutdown measures: The external load power supply line of the PLC should have voltage interruption protection measures. When the power supply is restored after a temporary power outage, do not press the "start" button that cannot be automatically started by the external load of the PLC. Another function of this wiring method is that when emergency shutdown is required in special circumstances, the load power can be cut off by pressing the "Emergency Stop" button and the "Emergency Stop" signal can be input to the PLC. (4) Limit protection may cause danger in certain situations, such as elevator level exceeding the limit, so limit protection is set. When the limit protection acts, the load power is directly cut off, and the signal is input into the PLC.