Output Block Pv Status; Set Point Selection And Limiting; Action On Fault Detection - Emerson FIELDVUE DVC6200f Instruction Manual

Note
You must wire BKCAL_OUT [25] to
BKCAL_IN [27] of the upstream block
that provides CAS_IN [17]. Otherwise,
the AO will not initialize properly, and
the setpoint at CAS_IN [17] will not be
passed to OUT [9].
An analog readback value, such as valve position, is
shown by the process value (PV [7]) attribute in
engineering units.
To support testing, you can enable simulation, which
allows you to manually set the channel feedback.
There is no alarm detection in the AO function block.
To select the manner of processing the SP and the
channel output value configure the setpoint limiting
options, the tracking options, and the conversion and
status calculations.

Output Block PV Status

The Output Block PV Status is determined by the
value of the PlantWeb Alerts Set PV Status parameter
in the transducer block (PWA_SET_STATUS [97]),
the Transducer Block mode, and enabled Active
PlantWeb alarms. Refer to table 4-11.

Set Point Selection and Limiting

To select the source of the SP [8] value use the
MODE [5] attribute. In Automatic (Auto) mode, the
local, manually-entered SP [8] is used. In Cascade
(Cas) mode, the SP [8] comes from another block
through the CAS_IN [17] input connector. In
RemoteCascade (RCas) mode, the SP [8] comes from
a host computer that writes to RCAS_IN [28]. The
range and units of the SP [8] are defined by the
PV_SCALE [11] attribute.
In Manual (Man) mode the SP [8] automatically tracks
the PV [7] value when you select the SP-PV Track in
Man I/O option in IO_OPTS [14]. This option can be
used to minimize valve movement when the AO block
is transitioned from Manual mode to Auto. You can
disable this option in OOS mode only.
The SP [8] value is limited to the range defined by the
setpoint high limit attribute (SP_HI_LIM [20]) and the
setpoint low limit attribute (SP_LO_LIM [21]).
November 2010
AO Function Block
In Auto mode, the rate at which a change in the SP [8]
is passed to OUT [9] is limited by the values of the
setpoint upward rate limit attribute (SP_RATE_UP
[19]) and the setpoint downward rate limit attribute
(SP_RATE_DN [18]). A limit of zero disables rate
limiting.
As shown in figure 4-8, the block executes a
percentage of the set point change each macrocycle.
For example, if the set point rate is set at 10% per
second and the macrocycle is 500 milliseconds (0.5
seconds or 50% of 1 second), then during the first
macrocycle the set point will change 5% (50% of the
10% per second rate). If the macrocycle is 750
milliseconds (0.75 seconds or 75% of 1 second), then
during the first macrocycle the setpoint will change
7.5% (75% of 10).
When the transducer block receives the setpoint
change from an AO block with rate limits, it will
smoothly move the valve to the requested setpoint at
the rate limit configured in the AO block.
In Auto mode, the converted SP [8] value is stored in
the OUT [9] attribute. In Man mode, the OUT [9]
attribute is set manually, and is used to set the analog
output defined by the CHANNEL [22] parameter.
You can access the actuator position associated with
the output channel through the READBACK [16]
parameter (in OUT units) and in the PV [7] attribute (in
engineering units). The digital valve controller supports
position feedback and therefore provides the actual
valve position in PV [7] and READBACK [16] directly.

Action On Fault Detection

To define the action you wish the valve to take when
the block is in CAS mode, and the CAS_IN [17] input
detects a communication failure, or is commanded to
go to fault state by the upstream block or the resource
block, configure the following parameters:
IO_OPTS [14]: Determines the action OUT [9] will
take upon a fault state. If the IO_OPTS [14] "Fault
State to Value" is not selected, then OUT [9] holds its
last position when Fault State is set. If "Fault State to
Value" is selected, OUT [9] goes to the FSTATE_VAL
[24] value when Fault State is set.
FSTATE_TIME [23]: The length of time, in seconds,
that the AO block will wait to set Fault State. When
Fault State is set, the OUT [9] value goes to either the
FSTATE_VAL [24] value or holds its last position,
depending on I/O_OPTS [14]. When the block has a
target mode of CAS, a fault condition will be detected
if the CAS_IN [17] has a BAD status or an Initiate
Fault State substatus is received from the upstream
block.
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