SLC 500 5/03 PID block- PV not wanting to be read by the PID block

Hello,

I have a PID block in my program controlling pump speed in order to get a correct Differential pressure.

The way I have it set up is the current DP is reading into the PV on the PID block. The DP is accurate and moving. The issue is, when I go into my PID setup screen the PV always reads 0. Which as you could probably understand is really throwing everything off. I do have a UL flag thrown which I am also trying to figure out but I don't think that should have anything to do with the PV.

Alright so I think I figured something out. I put in a new input into the PV and it took it. I:18.0. So can the PV only be an input value? It can't be on an N Table or is there other tables that will work?

Usually, the other way round. Typically, you take your input and scale it to a 0-16383 value then store as an integer. That integer is used for your PV. You can use the input directly as long as it does not exceed that range.

https://literature.rockwellautomation.com/idc/groups/literature/documents/rm/1747-rm001_-en-p.pdf
See page 198

OG

Figured it out. My pv was scaled for the actual pressure. I figured that if my pv and my sp were both scaled the same it wouldn't matter but apparenlty the equation doesn't work for that small of numbers. Once i scaled both to 0 to 16383 it worked.