Filter
Top Products
Appendix
C-1
C PID Function Block
The PID function block combines all of the necessary logic to perform
proportional/integral/derivative (PID) control. The block supports mode
control, signal scaling and limiting, feedforward control, override
tracking, alarm limit detection, and signal status propagation.
The block supports two forms of the PID equation: Standard and Series.
You can choose the appropriate equation using the FORM parameter.
The Standard ISA PID equation is the default selection.
BKCAL_IN = The analog input value and status from another
block’s BKCAL_OUT output that is used for
backward output tracking for bumpless transfer
and to pass limit status.
CAS_IN = The remote setpoint value from another function
block.
FF_VAL = The feedforward control input value and status.
IN = The connection for the process variable from
another function block.
PID
OUT
BKCAL_OUT
BKCAL_IN
CAS_IN
FF_VAL
IN
TRK_IN_D
TRK_VAL
TRK_IN_D = Initiates the external tracking function.
TRK_VAL = The value after scaling applied to OUT in
Local Override mode.
BKCAL_OUT = The value and status required by the
BKCAL_IN input of another function block
to prevent reset windup and to provide
bumpless transfer to closed loop control.
OUT = The block output and status.
FIELDBUS-FBUS_34A
Standard Out GAIN e 1
1
τ
r
s1+
-----------------
τ
d
s
ατ
d
s1+×
----------------------------++
× F+×=
Series Out GAIN e× 1
1
τ
r
s
-------
+
×
τ
d
s1+
ατ
d
s1+×
----------------------------
+ F+=
Where
GAIN: proportional gain value
τ
r
: integral action time constant (RESET parameter) in seconds
s: laplace operator
τ
d
: derivative action time constant (RATE parameter)
α: fixed smoothing factor of 0.1 applied to RATE
F: feedforward control contribution from the feedforward input (FF_VAL parameter)
e: error between setpoint and process variable