AO Function Block
December 2009
4-69
Figure 4-8. Analog Output (AO) Function Block
B2716-1 / IL
BKCAL OUT
OUT
CAS IN
BKCAL
OUT = The value and status required by the
BKCAL IN input of another block to
prevent reset windup and to provide
bumpless transfer to closed loop control.
CAS IN = The remote setpoint value from another
function block.
OUT = The block output and status.
AO
READBACK
READBACK = Actual valve position.
Analog Output (AO) Function Block
Overview
The Analog Output (AO) function block assigns an
output value to a field device through a specified I/O
channel. The block supports mode control, signal
status calculation, and simulation. Figure 4-9
illustrates the internal components of the AO function
block, and table 4-24 lists the definitions of the block
parameters. The digital valve controller measures and
uses actual valve position for READBACK [16].
Note
The AO block actual mode will not
move to Auto unless:
Resource Block actual mode is Auto, and
AO SHED_OPT [27] is set to a non-zero
value.
Note
Actual Block Mode
(MODE_BLK.ACTUAL [5.2]) will remain
out of service and the block cannot be
scheduled if the block has not been
licensed. Contact your Emerson
Process Management sales office to
upgrade product licensing.
Note
Actual Block Mode
(MODE_BLK.ACTUAL [5.2]) will remain
in IMAN and the block Readback
status will be Bad − Not Connected if
the Output Block Selection is set
incorrectly. From the transducer block
method Outblock Selection, select the
desired output block, see page 4-26.
Modes
The Analog Output function block supports the
following modes:
Manual (Man)—You can manually set the output
to the I/O channel through the OUT [9] attribute. This
mode is used primarily for maintenance, calibration
and diagnostics.
Automatic (Auto)—The block output (OUT [9])
reflects the target operating point specified by the
setpoint (SP [8]) attribute. Typically the setpoint is set
by the user.
Cascade (Cas)—The SP [8] attribute is set by
another function block through a connection to
CAS_IN [17]. The SP [8] value is used to set the OUT
[9] attribute automatically. This is the most frequently
used mode in the digital valve controller.
Note
The transducer block must be in Auto
for the mode to go to AUTO, CAS,
MAN, or RCAS.
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