Rosemount OCX 8800, Instruction Manual

Page: 139 / 266

Instruction Manual
IM-106-880, Rev 2.1
April 2017
OCX 8800
7-39
Figure 7-13. PID Function Block Schematic
FF_VAL
BKCAL_IN
TRK_IN_D
CAS_IN
IN
TRK_VAL
BKCAL_OUT
OUT
Setpoint Selection and
Limiting
The setpoint of the PID block is determined by the mode. You can configure
the SP_HI_LIM and SP_LO_LIM parameters to limit the setpoint. In
Cascade
or RemoteCascade mode, the setpoint is adjusted by another function block
or by a host computer, and the output is computed based on the setpoint.
In Automatic mode, the setpoint is entered manually by the operator, and the
output is computed based on the setpoint. In Auto mode, you can also adjust
the setpoint limit and the setpoint rate of change using the SP_RATE_UP and
SP_RATE_DN parameters.
In Manual mode the output is entered manually by the operator, and is
independent of the setpoint. In RemoteOutput mode, the output is entered by
a host computer, and is independent of the setpoint.
Figure 7-14 illustrates the method for setpoint selection.
FF_GAIN
FF_SCALE
Feedforward
Calculation
MODE
RCAS_OUT
ROUT_OUT
RCAS_IN
ROUT_IN
Setpoint
Limiting
and
Filtering
PID
Equation
Output
Limiting
Operator
Setpoint
SP_HI_LIM
SP_LO_LIM
SP_RATE_DN
SP_RATE_UP
SP_FTIME
GAIN
RATE
RESET
Scaling
and
Filtering
Alarm
Detection
OUT_HI_LIM
OUT_LO_LIM
OUT_SCALE
Operator
Output
PV_SCALE
PV_FTIME
HI_HI_LIM
HI_LIM
DV_HI_LIM
DV_LO_LIM
LO_LIM
LO_LO_LIM
Convert
TRK_SCALE
OUT_SCALE
3
8
7
4
0
0
9
2