What is a Deadman Switch in a PLC (Programmable Logic Controller), and how does it work?

What is a Deadman Switch?

A Deadman Switch in a PLC is a safety feature that stops a machine (or) process if the operator becomes incapacitated (or) unable to retain control.

To keep the system working, the operator must provide constant or periodic input, such as pressing & holding a button.

If the operator releases the button (or fails to provide input within a predetermined time frame), the switch automatically disconnects the power or control signal, bringing the process to an end.

Application of Deadman Switch

  • This is commonly used in hazardous jobs where the operator’s presence & attentiveness are crucial to safety.
  • In a PLC system, the Deadman Switch can be designed as part of the safety logic, causing the machine to stop working if the expected input is interrupted, preventing accidents and assuring operator safety.

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