DVC6000f Series
March 2006
5-66
Figure 5-8. 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 5-9
illustrates the internal components of the AO function
block, and table 5-24 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:
S Resource Block actual mode is Auto,
S AO CHANNEL [22] is set to 1,
S AO SHED_OPT [27] is set to a non-zero
value, and
S AO MODE_BLK.PERMITTED [5.3] Auto is
enabled.
Note
Feature Select in the resource block
must have the DO Control option
disabled for the AO block to be fully
functional.
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 or
MAN.
RemoteCascade (RCas)—The SP [8] is set by a
host computer by writing to the RCAS_IN [28]
parameter. The SP [8] value is used to set the OUT [9]
attribute automatically.
Out of Service (OOS)—The block is not
processed. The output channel is maintained at the
last value and the status of OUT [9] is set to Bad: Out
of Service. The BLOCK_ERR [6] attribute shows Out
of Service.
Initialization Manual (Iman)—The path to the
output hardware is broken and the AO block output will
remain at the last position. This means the transducer
block mode is Out of Service or Manual.
5
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