Emerson Rosemount OCX 8800 Reference Manual page 169

Foundation Fieldbus
Figure 7-15: PID function block setpoint selection
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) useing 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 can 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, you 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.
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