Hamilton Sundstrand Company Gas Fuel Metering Valve HFG2.0 - Manual (Page 48)

42 HFG2.0 USER GUIDE
3.4 Moving to Stop Position
The Stop position is a fail-safe position that may be set anywhere
between Home (zero position, Valve Closed) and maximum span
(maximum flow). The default value for Stop position is 0.0 inches, as
defined in the Set-Up parameters.
The actuator will move to the Stop position if the DEMAND signal is ≤ 2
mA (signal loss) at any time after the actuator has completed Homing. It
will also move to the Stop position if the RUN command is removed
during any of the running modes. See the flow chart in Figure 3-1.
3.5 Controlling Motion
Once the Home position has been established, the DEMAND current
determines subsequent positioning of the actuator, and thus the valve,
within its span. The valve will track the DEMAND signal as long as
DEMAND ≥ 4.1 mA and RUN is ON, and will apply up to the maximum
force to reach this DEMAND position. See Figure 3-2. This is defined as
the RUN state, and it is the normal operating mode for the HFG2.0.
The actuator firmware program will remain in this state as long as the
demand is greater than 4.1 mA.
Note: If RUN command is removed or position DEMAND ≤ 2 mA,
the actuator will go to the STOP position.
Home Position
The Home position correlates to a DEMAND signal of 4 mA. The Home
position is determined after Power Up or after the HFG2.0 has been reset.
Dead Band
While the Home position correlates to a DEMAND signal of 4 mA, the
actuator will only move for DEMAND signals ≥ 4.1 mA. The DEMAND
signal range between 4.0 mA and 4.1 mA is therefore considered a Dead
Band. See Figure 3-3.
Once a DEMAND signal ≥ 4.1 mA is detected, the actuator will move to
the position that correlates to that current level. See Interpolation of
DEMAND Signal
below.
Hysteresis Band
The actuator should return to the Home position when the DEMAND
Signal drops below the 4.1 mA Dead Band threshold. In practice,
hysteresis may result in the actuator not returning to Home position until
the DEMAND signal drops below a threshold as low as 4.08 mA. The
DEMAND signal range between 4.08 mA and 4.1 mA is therefore
considered the Hysteresis Band. See Figure 3-3.