Hi all,
I have an issue with a machine safety circuit.
The circuit contains a safety relay which when deemed in a safe condition can energizes two redundant contactors if both contactors are in the same state. The contactors have several normally open contacts as well as one each normally closed AUXILARY contact.
There is an electrical path to energize both contactors if both contactors are off and so a path through both contactors normally closed auxiliary contacts.
If both contactors are then on, there is a path through both contactor normally open contacts to remain on. (Safety relay also permitting a common path to +24VDC).
The problem arose when I had to replace the two contactor, which DID have all the required NO / NC contacts however both contactor do NOT have auxiliaries for the two NC contacts, as they were part of the main contactor.
Both contactors now just chatter on and off.
In testing other (unusable in this application) contactors with auxiliaries, I found that the normally closed contacts do not actually open UNTIL the normally open contacts are already closed! Both are actually close for a brief “pull in time”.
My questions are this:
Is this by design and how the original circuit might have worked?
Is there a natural delay between a contactors NC contacts opening until the NO contactors closing to ensure a path in both states (again unless the safety relay has already broken the path)?
Do all auxiliary contacts perform this way in relation to the main contacts by design for just such a requirement?
I do know if I order replacement contactors with NC auxiliaries the issue will be corrected for a few months until the contacts go bad (we have done this three times already). The contactors we try to add WITHOUT NC auxiliaries (but all the correct NO / NC main contacts will not work (just the chatter).
I would appreciate thoughts and info on this subject.
I have an issue with a machine safety circuit.
The circuit contains a safety relay which when deemed in a safe condition can energizes two redundant contactors if both contactors are in the same state. The contactors have several normally open contacts as well as one each normally closed AUXILARY contact.
There is an electrical path to energize both contactors if both contactors are off and so a path through both contactors normally closed auxiliary contacts.
If both contactors are then on, there is a path through both contactor normally open contacts to remain on. (Safety relay also permitting a common path to +24VDC).
The problem arose when I had to replace the two contactor, which DID have all the required NO / NC contacts however both contactor do NOT have auxiliaries for the two NC contacts, as they were part of the main contactor.
Both contactors now just chatter on and off.
In testing other (unusable in this application) contactors with auxiliaries, I found that the normally closed contacts do not actually open UNTIL the normally open contacts are already closed! Both are actually close for a brief “pull in time”.
My questions are this:
Is this by design and how the original circuit might have worked?
Is there a natural delay between a contactors NC contacts opening until the NO contactors closing to ensure a path in both states (again unless the safety relay has already broken the path)?
Do all auxiliary contacts perform this way in relation to the main contacts by design for just such a requirement?
I do know if I order replacement contactors with NC auxiliaries the issue will be corrected for a few months until the contacts go bad (we have done this three times already). The contactors we try to add WITHOUT NC auxiliaries (but all the correct NO / NC main contacts will not work (just the chatter).
I would appreciate thoughts and info on this subject.