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AB ControlLogix - SetPoint change monitoring?

AB ControlLogix - SetPoint change monitoring?

(OP)
A bit of a strange question here...
I have achieved what I need through just ladder programming, but I wonder if there is a more elegant solution.

My project requires displaying both Liters and Gallons.
The setpoints must be able to be input in both Liters and Gallons.
But, if I change the Liters SP, it must then auto-update the Gallons SP. Vice-versa if I change Gallons, then the Liters needs to change also.

Right now, the Ladder passes the "last" SP value to a holder. Then compares if the "last" does not equal "current" then MOV Current to Last AND MOV Current with scaling to Gallons.

Is there a function that will monitor my variable, then when there is a change, signal a .DN bit that I could do my Liters->Gallons from?

Devon Murray, EIT [Mechanical]
Solidworks 2011 SP 2.0

RE: AB ControlLogix - SetPoint change monitoring?

Yes you can.
After the compare, latch a bit (new data), then use this bit to trigger a timer, that gives you a .dn bit. after the .dn bit is true use the .dn bit to unlatch the bit. You could also count the changes by just oneshot the .dn bit for an add instruction.

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