Reference Manual
00809-0100-4793, Rev CA
August 2004
Rosemount 8742C
4-4
PID 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.
To further customize the block for use in your application, you can configure
filtering, feedforward inputs, tracking inputs, setpoint and output limiting, PID
equation structures, and block output action.
NOTE
Refer to the F
OUNDATION
fieldbus Block product manual, document
00809-0100-4783, for more details on configuring and troubleshooting the
PID Block.
Standard Out
GAIN
e
1
1
τ
r
s
1
+
-----------------
τ
d
s
α τ
d
s
1
+
×
----------------------------
+
+
×
F
+
×
=
Series Out
GAIN
e
×
1
1
τ
r
s
-------
+
×
τ
d
s
1
+
α τ
d
s
1
+
×
----------------------------
+
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
Summary of Contents for 8700 Series
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