stop button and plc's 1

[061282]

In a plc controlled system, can someone please tell me why I should use a normally closed stop pushbutton instead of a normally open pushbutton.

 

[AGomaa]

In most of alarm signals you would prefer to use Normally Closed signal. because in addition to your alarm status if you have a cut in the wire you will have alarm. which will indicate that there is a problem in your system. using normally open contact for such application (with the cut wire) you will never know that the wire is cut and you will never know that you have alarm.
It is the same reason for your Stop pushbutton

 

[dogleg43]

AGomaa (Chemical)is absolutely correct.

You want your logic to be "fail safe" and that is what a normally closed switch does for you. In the event of a failure (broken wire) you don't have to wait until you need the stop button to know that there is a problem.

 

[nbucska]

Not to mention it is better not to start than not be able to stop.

<nbucska@pcperipherals.com>

 

[skiier]

For cct supervision, but every one told you that.
A properly designed control system should "Estop" regardless of the state of any PLC inputs.Law in most countries.
Don't get this confused with a "cycle" stop, for example.