Hamilton Sundstrand Company Gas Fuel Metering Valve HFG2.0 - Manual (Page 46)

40 HFG2.0 USER GUIDE
this point, the HFG2.0 has no information about the position of the
actuator extension shaft.
When the HFG2.0 receives the RUN command, it will initiate motion in
the homing direction. The default homing direction for the HFG2.0 is
“Extend”. This means that the first movement after Power Up or Reset will
be an extension of the actuator in the HFG2.0. The actuator will extend at
the rate specified by the Homing Velocity in the Set Up parameters
(default is 0.5 in/sec) until a mechanical stop is encountered. In the
HFG2.0, this stop reached when the poppets seat in the orifices, thus
closing the valve. The HFG2.0 recognizes that a mechanical stop has
been reached when the actuator velocity drops to 0.05 in/sec or less.
The HFG2.0 will then slowly increase the motor current until the current
level corresponding to the Maximum Homing Force has been applied.
This Maximum Homing Force is also specified in the Set Up parameters
and has a default value of 500 lbf. When the pre-determined motor
current limit is reached, the HFG2.0 defines this valve position as Home.
Home is “Valve Closed” for the HFG2.0. The system will then transition to
the Holding Motor Current State. See the flow chart in Figure 3-1 for an
overview of this process.
The DEMAND current determines subsequent positioning of the actuator,
and thus the valve, within its span once the Home position has been
established
See Section 3.8 for additional information about Set-Up parameters.
3.3 Holding Motor Current State
In the Holding Motor Current state, the actuator applies a constant
Holding Force. This feature allows the Home position to thermally expand
or contract without damaging the HFG2.0. This Holding Force is specified
in the Set Up parameters and has a default value of 500 lbf.
The system is in the Holding Motor Current state immediately after
Homing. The system will also move into this state when the DEMAND
signal is > 2mA and < 4.1mA. See the flow chart in Figure 3-1.