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TheJacobsDad

Limit Setpoint Changes per Min

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Hi All,

I am working on a CompactLogix Processor using Studio v30.

I have a UDT set up as setpoints which works fine and I use in a few sequences in my code. The setpoints are changed from SCADA (Wonderware)

I would like to limit a couple of setpoints so they may only be changed 3 times a minute and a maximum of 10 changes in 1 hour, can anyone come up with an elegant way to manage this in the PLC  ? I want to achieve this using minimal timers/counters.

 

Thanks in advance

 

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Just thinking out loud here....

Could you use  FIFO stack? FFL and FFU instructions. Whenever there's a setpoint change, add the current date/time using FFL. You would use 2 FIFO stacks: one for the 3/min limit and the other for the 10/hour limit. Compare the oldest record in the FIFO to the current date/time. If the oldest record is older than a minute (or an hour), use FFU to unload it. If the length parameter reaches 3 for the 3/min stack or 10 for the 10/hour stack, block further changes.

I wish I had a CPU on my desk I could test this with. I'd like to tinker with it.

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