Fisher FIELDVUE DVC6200f Instruction Manual page 119

Instruction Manual
D103412X012
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]).
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.
Detailed Setup—AO Function Block
July 2013
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