JohdotaAn emergency stop stops the machine in a hazardous situation. When the emergency stop button is released, the machine must not start by itself. The emergency stop is reset as a separate step, and only after that is the machine started in the normal way.
Reset relay
In a simple control circuit, reset relay K2 keeps track of the emergency stop state. Emergency stop S0 is in series with K2, and reset button S3 energises K2, which latches. The control of the other contactors starts from an NO contact of K2, so the emergency stop drops out everything at once.
Safety relay
On more demanding machines a safety relay monitors the emergency stop on two channels. The motor is then often controlled by two contactors in series, and their NC contacts are wired into the reset circuit of the safety relay. If a contactor has welded shut, the reset does not succeed.
Remember
- The NC contacts of an emergency stop button have direct opening action (positive opening).
- The reset must not start the machine. Starting is always a separate action.