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Full Span Position (Maximum Flow)
The Full Span (Maximum Flow) position correlates to a DEMAND signal
of 20 mA. The maximum Span possible for the HFG2.0 is 1.0 inches due
to the configuration of the valve assembly. The maximum Span possible
for the actuator used in the HFG2.0 is 2.0 inches due to its mechanical
configuration.
The Span value in the Set-Up parameters has a default setting of 1.0
inches of retraction to allow for the distance between the mechanical stop
in the valve and the mechanical stop in the actuator. (The default
definition of Home is Extend, so default Span is a retraction.)
Interpolation of DEMAND Signal
Linear interpolation of the DEMAND signal in the range between 4 mA
and 20 mA is the default condition, as specified in the Set-Up parameters.
With linear interpolation, a DEMAND signal of 12 mA (midway in range of
DEMAND signal) will correlate to a position at 0.5 inches (midway in the
1.0 inch span). See Figure 3-2 for an illustration of linear interpolation.
Note: The actuator and valve position is linear relative to the
DEMAND signal in the default condition. However, due to
the physical profile of the poppets, orifices and soft seats,
the resultant flow area will NOT be linear relative to the
DEMAND signal.
Figure 3-2. HFG2.0 Actuator Position vs. DEMAND, with default conditions
Home as a Mech. Stop in HFG2.0
CH. 3: OPERATING THE HFG2.0 43