Good Morning All,
I have a design problem that has been bugging me for a week or so, and would like to get some expert opinions.
It is, how do you generally wire contactor feed backs.
I normally wire mine to a normally open auxillary contact, so that if it dosn't close I can generate an alarm. I also usually generate a 'Fail to Open' alarm as well, however if only one, or maybe two, contacts weld together it is possible for the auxillary to open but still have this faulted condition.
In safety circuits, this problem is overcome by wiring in the normally closed contact to the feedback. This is normally wired to a safety relay so that if a contact welds, the normally closed contact cannot close and the safety circuit cannot reset (this also assumes a second, backup, contactor or a failure warning alarm).
My problem is, should I wire normal control circuit contactor feedbacks to the normally closed auxillary? This would help detect contact welds much better than the normally open auxillary, but may not detect that the contactor has correctly closed.
A third option is to wire a feedback to both a normally open and normally closed auxillary, assuming these are both available. This also has the problem of expanding the I/O count.
I was wondering what are your opinions and experiences with this problem? How would you go about it?
TIA
Doug
I have a design problem that has been bugging me for a week or so, and would like to get some expert opinions.
It is, how do you generally wire contactor feed backs.
I normally wire mine to a normally open auxillary contact, so that if it dosn't close I can generate an alarm. I also usually generate a 'Fail to Open' alarm as well, however if only one, or maybe two, contacts weld together it is possible for the auxillary to open but still have this faulted condition.
In safety circuits, this problem is overcome by wiring in the normally closed contact to the feedback. This is normally wired to a safety relay so that if a contact welds, the normally closed contact cannot close and the safety circuit cannot reset (this also assumes a second, backup, contactor or a failure warning alarm).
My problem is, should I wire normal control circuit contactor feedbacks to the normally closed auxillary? This would help detect contact welds much better than the normally open auxillary, but may not detect that the contactor has correctly closed.
A third option is to wire a feedback to both a normally open and normally closed auxillary, assuming these are both available. This also has the problem of expanding the I/O count.
I was wondering what are your opinions and experiences with this problem? How would you go about it?
TIA
Doug