Output selection and limiting
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 or RemoteOutput mode, the output may be entered manually. You
can limit the output by configuring the OUT_HI_LIM and OUT_LO_LIM parameters.
Bumpless transfer and setpoint tracking
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 a specified
mode.
You 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). If the Use PV for BKCAL_OUT option is not selected,
the working setpoint (SP_WRK) is used for BKCAL_OUT.
You 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).
7.9.2
PID equation structures
Configure the STRUCTURE parameter to select the PID equation structure. You can select
one of the following choices:
• PI Action on Error, D Action on PV
• PID Action on Error
• I Action on Error, PD Action on PV
Set RESET to zero to configure the PID block to perform integral only control regardless of
the STRUCTURE parameter selection. When RESET equals zero, the equation reduces to an
integrator equation with a gain value applied to the error.
Foundation Fieldbus
160 OCX 8800
To Next Page
Loading...
