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Old February 28th, 2011, 03:01 PM   #1
Rob735
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VFD control with a 4~20ma signal

Hey Guys, I am looking for some suggestions on controlling a VFD with a 4~20ma signal from a ML1400 with a spectrum 1762sc-0f8 expansion card.

I have been trying to us a PID control but am not happy with how wrappedly the output moves.

Also I am not sure how I am going to program my ramp up time as it is required to start and runn at minimum speed for 16 minutes before it will then begin to let the VFD work its magic.

Any suggestions on how to hold it at it's minimum?

Rob
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Old February 28th, 2011, 03:23 PM   #2
Tom Jenkins
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Use a move statement to load a register with the min speed, and a timer initiated by the start command. When the timer times out open a NC contact to disable the move, and use a NO command to enable the rungs or subroutine for the variable speed control.
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