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Emergency Stop Button Working Principle
- Jun 05, 2018 -

(1) From the operation time point, the time from closing to opening of the normally closed contact is much shorter than the time from the natural state to closing of the normally open contact.

(2) From the button mechanism, whether the emergency stop button is a normally-closed or normally-open contact, if the button is not in place (pressed to the end), the emergency stop button will spring up again, thus make the operation invalid. When using the normally open contact, if the emergency stop button is not in place, the emergency stop doesn’t work (because the normally open contact is not closed); but it’s different when using the normally closed contact, regardless of whether the emergency stop is in place, only the contact acts, and the emergency stop will work.

(3) From the perspective of its control line, the most basic function of the emergency stop button is emergency stop in emergency situations to avoid mechanical accidents or personal accidents. But, because of the long-term operation of the machine, the line, especially the part of the emergency stop line, may cause the circuit broken. At this time, if the emergency stop button uses the normally open contact, the line failure of the emergency stop part will not be found. And if is with a normally closed contact, when the emergency stop line fails, at most it will cause the machine to stop, and the loss will be relatively small. Basing on the above several reasons, the emergency stop button preferably uses a normally closed contact when designing the electrical control system.

(4) When an emergency stop button is pressed in one area, one pair of contacts cuts off the operation of the power equipment that needs to be stopped in the area, and the other pair of contacts enters the PLC, and cuts off the starting circuit of the power equipment controlled by the PLC.