output bits

Larry Painter · Nov 29, 2014

In a simple rung two inputs are true, however the output bit does not go true. How can this happen and what do I do to fix it?
This is a AB PLC 5 with standard 120v output cards.

FluxCap · Nov 29, 2014

Either the output is being used in another rung that is holding it off, or the subroutine isn't being called.

Davek0974 · Nov 29, 2014

Fallen into this plenty of times

As said, check that output is not being used as an output on another rung, the "find all" function is good for this.

Mickey · Nov 29, 2014

Post your program, its .RSP file. Zip it furst.

Frankw@Pacs · Dec 4, 2014

this may be silly, but can you be more specific?
is the Output not turning on in the ladder logic, or is the field device not working?

point being- I am currently working on a PLC 5 120V output myself and at first I didn't realize they were isolated outputs. The card I'm using is a 1771-OD16.

FluxCap · Dec 4, 2014

From your description, the PLC output isn't turning on. If you have another ring of logic somewhere referencing the same output, the PLC will do whichever rung executes last.

Aabeck · Dec 4, 2014

Another thing to check - is the PLC in Run or Program mode?

If in a ladder other than Ladder 2, make sure there is a JSR to that ladder.

And do like Davek0974 says, right click on the output & click on Find All; in the results box see if there is more than one OTE, or maybe a OTU unlatch somewhere too. The last scanned line with the output rules.

output bits

Larry Painter

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