FAURE-HERMAN
COMPONENT MAINTENANCE MANUAL
744-082 / 744-082-3
28-49-91
PAGE 5/6
MAR 31/07
4.
OPERATION
A.
Operating principle (See figure 2)
The various circuit supplies are fed by a regulated 28 V DC external power source.
A selector and two switches inform the microprocessor of the operating mode, the type of
helicopter and unit of measure selected. According to these indications, the microprocessor
processes the previously reshaped signals delivered by the transmitters, in order to calculate the LH
and RH instant flow rates, the remaining quantity of fuel and the remaining flight time.
The calculations are made using programs stored in the EPROM. The RAM is used for data
storage.
The data concerning the type of helicopter and the unit of measure selected are sent to the display
by the microprocessor.
A watchdog is used to reset the RAM and the microprocessor at the request of the microprocessor
or when a power supply failure occurs.
A spare indicator light comes on when the calculated flight time limit is less than 40 min.
The microprocessor controls the temperature via two thermistors located in the transmitters.
In the event of a 28 V power cutoff, a backup battery is used to save the data stored in the RAM.
B.
Detailed operation (See figure 3)
(1)
Power supplies (See sheet 1)
The 28 V mains voltage is protected and filtered to supply spare indicator light DS7 and the
circuits which generate the operating voltages.
(a)
28 V control
The 28 V mains voltage is applied to comparator IC2 which controls transistor T1.
This transistor is saturated when the mains voltage drops below 18.2 V and the 28 V
validity signal disappears. When the mains voltage is correct, the validity signal
returns to 5 V.
The document reference is online, please check the correspondence between the online documentation and the printed version.
