GE PACSystems RX7i

Chapter 7. PID Built-In Function Block
362 PACSystems* RX7i, RX3i and RSTi-EP CPU Programmer's Reference Manual GFK-2950C
7.6.3 Ideal Tuning Method
The Ideal Tuning procedure provides the best response to SP changes that are delayed only by the T
p
process delay or dead time.
1. Determine the three process model parameters, K, Tp and Tc for use in estimating initial PID loop
gains.
2. Calculate Kp, Ki, and Kd as follows:
Kp = 2 * T
c
/ (3 * K * T
p
)
Ki = T
c
Kd = Ki/4 if Derivative term is used
3. Once initial gains are determined, convert them to integers.
4. Calculate the Process gain, K, as a change in input PV Counts divided by the resulting output step
change in CV Counts. (Not in process PV or CV engineering units.) Specify all times in seconds.
5. Once Kp, Ki and Kd are determined, Kp and Kd are multiplied by 100 while Ki is multiplied by
1000. The resulting values are entered into the corresponding reference array word locations.