Flowserve MX FOUNDATION Fieldbus Field Unit - Manual (Page 35)

35
MX/QX FOUNdaTION Fieldbus Field Unit FCd LMENIM2330-01 – 08/11
flowserve.com
Figure 3.6 – Proportional Integral Derivative Function Block
Setpoint selection and limiting
The setpoint of the PID block is determined by the mode. One can configure the SP_HI_LIM and
SP_LO_LIM parameters to limit the setpoint. In Cascade or Remote Cascade 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, one 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
Remote output mode, the output is entered by a host computer, and is independent of the setpoint.
Filtering
The filtering feature changes the response time of the device to smooth variations in output readings
caused by rapid changes in input. One can configure the filtering feature with the FILTER_TYPE
parameter, and one 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
One can enable the use of output tracking through the control options. One 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.