Can AB PLC-5 Take Negative Values for PID PV?

[skyfox]

Up to date, I've only had to deal with Positive PV values with my PID controls where Zero was the absolute Minimum value in to the PID PV register. Now I am trying to maintain a certain pressure/Vaccum in a duct where an operator can enter a setpoint anywhere from -2 to +4 PSID. Range of the Instrument is -5 to +5 PSID. Can I feed this scaled -5 to +5 PV signal directly to a PLC-5 PV register or do I need to scale it to a positive value?

Thanks All

 

[Mickey]

Yes and no.

Your PV input must be somewhere between 0-4095. But the Scaled min (Smin) and Scaled Max (Smax) can have a negative number. See PDF below for an exert from the manual. Also a link to the instruction set for your PLC5 if you don't have it.

http://literature.rockwellautomation.com/idc/groups/literature/documents/rm/1785-rm001_-en-p.pdf

 

[skyfox]

Thanks Mickey

Much appreciated.

 

[Mickey]

Thanks Mickey

Much appreciated.

Your welcome. Let us know how it works out.