Rosemount OCX 8800, Instruction Manual

Page: 135 / 266

Instruction Manual
IM-106-880, Rev 2.1
April 2017
OCX 8800
7-35
d
T
d
s
+
1
T
s
r
T
a
+
d
PROPORTIONAL/
INTEGRAL/DERIVATIVE
(PID) FUNCTION BLOCK
BKCAL_IN
CAS_IN
FF_VAL
IN
TRK_IN_D
TRK_VAL
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.
BKCAL_OUT
OUT
TRK_IN_D = Initiates the external tracking function.
TRK_VAL = The value after scaling applied to OUTin
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.
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.
1
Standard Out = GAIN
x
e
x
1 +
T
s
+
1
+ +
F
Series Out = GAIN
x
e
x
1
+
1
T
r
s
T
s
+
1
a
x
T
d
s
+
1
Where
GAIN: proportional gain value
r: Integral action time constant (RESET parameter) in seconds
s: laplace operator
d: derivative action time constant (RATE parameter)
: fixed smoothing factor of 0.1 applied to RATE
F: feedforward control contribution from the feedforward input (FF_VALparameter)
e: error between setpoint and process variable
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. Table 7-26 lists the PID block
parameters and their descriptions, units of measure, and index numbers, and
Figure 7-13 illustrates the internal components of the PID function block.
3
8
7
4
0
0
9
1
3
8
7
4
0
0
9
0
+
F
PID