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gromit

PLC5 First-out logic

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Does anyone have PLC5 First-out logic?

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gromit please elaborate on what you mean by First Out logic.  Do want a First In First Out Buffer logic for a PLC 5 or do you want logic which watches an array of Binary bits and determines which one made first?

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BobLfoot,

I believe the latter is what I am looking for, whereby the first bit in a trip string latches in as the culprit that caused the trip...ergo first-out.

thanks

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Gromit,

First out logic, in the power and chemical industry definition, is not really feasible in Rockwell PLCs.  This is due to the order of processing.  What I mean is that the ladder is scanned from left to right and then top to bottom.

In my experience, the Modicon X84 series was much better at first out logic.  This due to it's scanning top to bottom and then left to right.

If you really want to try, just pay specific attention order of processing and write your ladder with "prioritization" in mind.  In other words higher criticality and likelihood of occurrence. 

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Thanks pcmccartney1. At the end of the day I finally built and tested the first-out logic as solicited.

The average program scan time is under 20 msec, which contributes to the successful operation of the first-out scheme.

As mentioned, I fully tested it today with no errors.

Tomorrow, we will be starting the skid/system and the first-out logic will be required to assist with identifying inputs which cause intermittent trips or shut downs.

FIRSTOUT.pdf

FIRSTOUT.RSP

Edited by gromit

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