Rosemount OCX 8800, Instruction Manual

Page: 140 / 266

Instruction Manual
IM-106-880, Rev 2.1
April 2017
OCX 8800
7-40
Figure 7-14. PID Function Block
Setpoint Selection
Operator
Setpoint
SP_HI_LIM
SP_LO_LIM
SP_RATE_UP
SP_RATE_DN
Auto
Man
Setpoint Rate
Auto
Man
Cas
Limiting Limiting
Cas
Filtering
The filtering feature changes the response time of the device to smooth
variations in output readings caused by rapid changes in input. You can
configure the filtering feature with the FILTER_TYPE parameter, and you can
adjust the filter time constant (in seconds) using the PV_FTIME or SP_FTIME
parameters. Set the filter time constant to zero to disable the filter feature.
Feedforward Calculation
The feedforward value (FF_VAL) is scaled (FF_SCALE) to a common range
for compatibility with the output scale (OUT_SCALE). A gain value (FF_GAIN)
is applied to achieve the total feedforward contribution.
Tracking
You enable the use of output tracking through the control options. You can set
control options in Manual or Out of Service mode only.
The Track Enable control option must be set to True for the track function to
operate. When the Track in Manual control option is set to True , tracking can
be activated and maintained only when the block is in Manual mode. When
Track in Manual is False , the operator can override the tracking function
when the block is in Manual mode. Activating the track function causes the
block’s actual mode to revert to
Local Override .
The TRK_VAL parameter specifies the value to be converted and tracked into
the output when the track function is operating. The TRK_SCALE parameter
specifies the range of TRK_VAL.
When the TRK_IN_D parameter is True and the Track Enable control option
is True , the TRK_VAL input is converted to the appropriate value and output in
units of OUT_SCALE.
Output Selection and
Limiting
Bumpless Transfer and
Setpoint Tracking
Output selection is determined by the mode and the setpoint. In Automatic ,
Cascade , or RemoteCascade mode, the output is computed by the PID
control equation. In Manual and RemoteOutput mode, the output may be
entered manually. You can limit the output by configuring the OUT_HI_LIM
and OUT_LO_LIM parameters.
You can configure the method for tracking the setpoint by configuring the
following control options (CONTROL_OPTS):
SP-PV Track in Man
— Permits the SP to track the PV when the target mode
of the block is Man.
SP-PV Track in LO or IMan
— Permits the SP to track the PV when the
actual mode of the block is Local Override (LO) or Initialization Manual
(IMan).
When one of these options is set, the SP value is set to the PV value while in
the specified mode.
3
8
7
4
0
0
9
3