Rosemount OCX 8800, Instruction Manual

Page: 141 / 266

Instruction Manual
IM-106-880, Rev 2.1
April 2017
OCX 8800
7-41
You can select the value that a master controller uses for tracking by
configuring the
Use PV for BKCAL_OUT control option. The BKCAL_OUT
value tracks the PV value. BKCAL_IN on a master controller connected to
BKCAL_OUT on the PID block in an open cascade strategy forces its OUT to
match BKCAL_IN, thus tracking the PV from the slave PID block into its
cascade input connection (CAS_IN). If the
Use PV for BKCAL_OUT option is
not selected, the working setpoint (SP_WRK) is used for BKCAL_OUT.
You can set control options in Manual or Out of Service mode only. When
the mode is set to Auto , the SP will remain at the last value (it will no longer
follow the PV.
PID Equation Structures
Configure the STRUCTURE parameter to select the PID equation structure.
You can select one of the following choices:
• PI Action on Error, D Action on PV
• PID Action on Error
• I Action on Error, PD Action on PV
Set RESET to zero to configure the PID block to perform integral only control
regardless of the STRUCTURE parameter selection. When RESET equals
zero, the equation reduces to an integrator equation with a gain value applied
to the error:
GAIN
x
e(s)
s
Where
GAIN: proportional gain value
e: error
s: laplace operator
Reverse and Direct
Action
To configure the block output action, enable the Direct Acting control option.
This option defines the relationship between a change in PV and the
corresponding change in output. With
Direct Acting enabled (True), an
increase in PV results in an increase in the output.
You can set control options in Manual or Out of Service mode only.
NOTE
Track Enable, Track in Manual, SP-PV Track in Man, SP-PV Track in LO
or IMan, Use PV for BKCAL_OUT
, and Direct Acting are the only control
options supported by the PID function block. Unsupported options are not
grayed out; they appear on the screen in the same manner as supported
options.
Reset Limiting
The PID function block provides a modified version of feedback reset limiting
that prevents windup when output or input limits are encountered, and
provides the proper behavior in selector applications.
Block Errors
Table 7-27 lists conditions reported in the BLOCK_ERR parameter.
Conditions in
italics are inactive for the PID block and are given here only for
your reference.
3
8
7
4
0
0
9
4