Working principle of emergency stop switch
1) In terms of action time, the time for normally closed contacts to close and open is much shorter than the time for normally open contacts to close from their natural state. Perhaps you have to say, how much less can it be? It doesn't matter how short the time is. But I have to say, this is particularly important when there is a danger that requires an emergency stop. At this point, even in milliseconds or microseconds, the shortest amount of time is crucial. You should know that accidents happen within a very short period of time. You can think about it, in such a short period of time, using normally open contacts may not have stopped the machine or disconnected the switch, causing significant machine damage or personal injury accidents. But using normally closed contacts may potentially stop the machine or shorten the duration of electric shock, avoiding all of this from happening.
2) From the perspective of button mechanism, we know that the emergency stop switch, whether it is a normally closed or normally open contact, will bounce up again if not pressed in place (fully pressed), thereby rendering the action ineffective. When using normally open contacts, if the emergency stop switches is not pressed in place, the emergency stop has no effect (because the normally open contacts are not closed); When using normally closed contacts, it's different. Regardless of whether the emergency stop button is pressed properly, the emergency stop only works when the contact is activated.
3) From its control circuit, it goes without saying that the most basic function of the emergency stop switches is to stop the vehicle in case of an emergency, avoiding mechanical or personal accidents. However, due to the prolonged operation of the machine, the circuit, especially the emergency stop circuit, may cause faults and open circuits. At this point, if the emergency stop switch uses a normally open contact, the circuit fault in the emergency stop section will not be detected. If it is discovered again when the emergency stop switch is used, it will be too late. When using normally closed contacts, if the emergency stop circuit fails, it will at most cause the machine to stop, and the losses will be relatively small. It is precisely for the above reasons that when designing an electrical control system, it is best to use normally closed contacts for the emergency stop switchses.
4) When the emergency stop switches of an area is pressed, one pair of contacts cuts off the operation of the power equipment that needs to be stopped in that area, while the other pair of contacts enters the PLC and cuts off the starting circuit of the power equipment controlled by the PLC.
