Flowserve MX FOUNDATION Fieldbus Field Unit - Manual (Page 36)

MX/QX FOUNdaTION Fieldbus Field Unit FCd LMENIM2330-01 – 08/11
36
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
Output selection is determined by the mode and the setpoint. In Automatic, Cascade, or Remote
cascade mode, the output is computed by the PID control equation. In Manual and Remote output
mode, the output may be entered manually. One can limit the output by configuring the OUT_HI_LIM
and OUT_LO_LIM parameters.
Bumpless transfer and setpoint tracking
One 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.
One 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). One 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).
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.
Modes
The PID function block supports the following modes:
MANUAL (MAN)—The block output (OUT) may be set manually.
AUTOMATIC (AUTO)—The SP may be set manually and the block algorithm calculates OUT.
CASCADE (CAS)—The SP is calculated in another block and is provided to the PID block through the
CAS_IN connection.
REMOTE CASCADE (RCAS)—The SP is provided by a host computer that writes to the RCAS_IN
parameter.
REMOTE OUTPUT (ROUT)—The OUT IS provided by a host computer that writes to the ROUT_IN
parameter.
LOCAL OVERRIDE (LO)—The track function is active. OUT is set by TRK_VAL. The BLOCK_ERR
parameter shows Local override.
INITIALIZATION MANUAL (IMAN)—The output path is not complete (for example, the cascade-to-
slave path might not be open). In IMan mode, OUT tracks BKCAL_IN.
OUT OF SERVICE (O/S)—The block is not processed. The OUT status is set to Bad: Out of Service.
The BLOCK_ERR parameter shows Out of service.