PID Block - Algorithms | iFIX 6.1 Documentation

The steady state PID block algorithm is:

The following table identifies the variables for the algorithm.

Variable	Value
	yn - yn-1 where: yn is the current output yn-1 is the previous output
Kp	100/PB
En	sp - pv (or the error at current scan time) where: sp is the set point pv is the current input
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:

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PID Block – Algorithms