Owner's manual

FOUNDATION
TM
Fieldbus Blocks Manual
3-4
Setpoint Selection
and Limiting
To select the source of the SP value use the MODE attribute. In
Automatic (Auto) mode, the local, manually-entered SP is used. In
Cascade (Cas) mode, the SP comes from another block through the
CAS_IN input connector. In RemoteCascade (RCas) mode, the SP comes
from a host computer that writes to RCAS_IN. The range and units of
the SP are defined by the PV_SCALE attribute.
In Manual (Man) mode the SP automatically tracks the PV value when
you select the SP-PV Track in Man I/O option. The SP value is set equal
to the PV value when the block is in manual mode, and is enabled
(True) as a default. You can disable this option in Man or O/S mode
only.
The SP value is limited to the range defined by the setpoint high limit
attribute (SP_HI_LIM) and the setpoint low limit attribute
(SP_LO_LIM).
In Auto mode, the rate at which a change in the SP is passed to OUT is
limited by the values of the setpoint upward rate limit attribute
(SP_RATE_UP) and the setpoint downward rate limit attribute
(SP_RATE_DN). A limit of zero prevents rate limiting, even in Auto
mode.
Conversion and
Status Calculation
The working setpoint (SP_WRK) is the setpoint value after limiting.
You can choose to reverse the conversion range, which will reverse the
range of PV_SCALE to calculate the OUT attribute, by selecting the
Increase to Close I/O option. This will invert the OUT value with
respect to the setpoint based on the PV_SCALE and XD_SCALE.
In Auto mode, the converted SP value is stored in the OUT attribute. In
Man mode, the OUT attribute is set manually, and is used to set the
analog output defined by the CHANNEL parameter.
You can access the actuator position associated with the output channel
through the READBACK parameter (in OUT units) and in the PV
attribute (in engineering units). If the actuator does not support position
feedback, the PV and READBACK values are based on the OUT attribute.
The working setpoint (SP_WRK) is the value normally used for the
BKCAL_OUT attribute. However, for those cases where the READBACK
signal directly (linearly) reflects the OUT channel, you can choose to
allow the PV to be used for BKCAL_OUT by selecting the Use PV for
BKCAL_OUT I/O option.
NOTE
SP_PV Track in Man, Increase to Close, and Use PV for BKCAL_OUT
are the only I/O options that the AO block supports. You can set I/O
options in Manual or Out of Service mode only.
Simulation When simulation is enabled, the last value of OUT is maintained and
reflected in the field value of the SIMULATE attribute. In this case, the
PV and READBACK values and statuses are based on the SIMULATE
value and the status that you enter.