TechTalk - SCADAPack : PID Reverse Acting Valve Logic

TechTalk - SCADAPack : PID Reverse Acting Valve Logic

Below is a typical PID logic for a SCADAPack.

Xybernetics SCADAPack - PID Reverse Acting Valve Logic

Highlighted below are three block that facilitates reverse acting function. Techanically what is does is as follows.

(1) MULF (Multiply floating-point values)
Multiplies output values from the PID function block by -1

(2) ADDF (Add Floating-point Values)
Add the output from MULF from Step (1) by 100 (which give the reverse acting output from PID)

(3) FTOU (Floating-point to Unsigned Integer)
Assigned the output from ADDDF from Step (2) into an unsighed integer

Xybernetics SCADAPack - PID Reverse Acting Valve Logic

If you want to use direct acting, just use the output from the PIDA function block (Modbus register 40590)

I hope it helps.