The steady state PID block algorithm is:
The following table identifies the variables for the algorithm.
|
Variable |
Value |
|
yn - yn-1 where: |
|
Kp |
100/PB |
|
En |
sp - pv (or the error at current scan time) where:
|
|
T |
Scan time (or sample time). |
|
Fn |
Feedback tag value. |
|
En-1 |
Error at previous scan time (1 scan time prior to current). |
|
TI |
Reset time constant (minutes/repeat). |
|
TD |
Derivative time constant (minutes). |
|
Derivative mode filter |
|
Proportional action constant |
|
Derivative action constant |
The new output of the PID block is:
