Dry Contact Alarm into a Isolated Input Card

BillRobinson · Mar 17, 2009

Hi all,

I had a engineer move an alarm input from an isolated digital input Card (AB 1756-IA16I) to a regular digital input card (AB 1756-IA16).

He made the change because "the device was supplied with dry contacts for alarm outputs".

I am unable to contact him this week to ask him why he had to do this, so I going to through this one out to the PLCS.net community.

Any thoughts?

Clay B. · Mar 17, 2009

If the device is using dry contacts as outputs then it is isolated.

Think of it this way. Instead of the isolation taking place on the PLC input card it is taking place on the device. As long as the power used to run thru the dry contact is common to the plc card everything is good.

BillRobinson · Mar 17, 2009

Yes I agree, but if you left the device on the Isolated PLC card, will it work without any issues? It would just be a waste of a isolated PLC channel?

Mickey · Mar 17, 2009

BillRobinson said:
Yes I agree, but if you left the device on the Isolated PLC card, will it work without any issues? It would just be a waste of a isolated PLC channel?

Yes.

Money4Nothing · Mar 17, 2009

Yes the device would still have worked on the isolated input card, but it would kind of be wasteful because its not using the capability that you specifically get when using an isolated card. Its unnessary to use an isolated card to monitor dry contacts.

If there are other I/O points being used on both of those cards, the engineer may have moved the point from one card to the next just for the sake of functional partitioning.

$

upendra_sp · May 4, 2010

I have ten alarms how do you find which alarm is ringed first, here all the ten alarm can ring at a time any can help in this ..

bernie_carlton · May 4, 2010

Start your own thread.

upendra_sp · May 5, 2010

thank you

sir please kindly briefly explain me how we can identify which alarm is ringing using plc,

my question was, see i have 10 alarm as input and display which alarm ringed first. which is the medium to recognize which alarm is first because all alarms can ring at a time. please give me your feedback sir. i am new too this plc programming.

Paul B · May 5, 2010

upendra_sp, welcome to the forum. Mr. Carlton is telling you to start a new question - called a thread. This is better than adding your new question at the end of an existing thread - which is over a year old.

So instead of clicking on "post reply" at the top left of an existing thread, you want to go here:
http://www.plctalk.net/qanda/forumdisplay.php?f=2
and click on "start a new thread", the green button at the top left.

Start a new thread, then ask your question.

shooter · May 5, 2010

bill tell the engineer it can be a safety issue now. The alarm will not be activated when any short in the line. So that is why isolated is used.
I do know it is easier and cheaper to use not isolated, however it has drawbacks.
or he does not have correct card with him.
just ask the man.
i do same btw as problems have to be solved.

Dry Contact Alarm into a Isolated Input Card

BillRobinson

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Clay B.

Lifetime Supporting Member

BillRobinson

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Mickey

Lifetime Supporting Member

Money4Nothing

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upendra_sp

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bernie_carlton

Lifetime Supporting Member + Moderator

upendra_sp

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Paul B

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shooter

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