FAURE-HERMAN
COMPONENT MAINTENANCE MANUAL
744-082 / 744-082-3
28-49-91
PAGE 22
MAR 31/07
(8)
Shaping the signals delivered by the transmitters (See sheet 2)
The signals delivered by the RH transmitter are amplified and filtered (circuit IC7). The
filter/amplifier output signals are chopped by diode CR300 before being sent to the input of
Schmitt trigger IC9 (1) which generates 5 V rectangular pulses.
The signals delivered by the LH transmitter are shaped likewise using circuits IC16 and D08,
before being sent to Schmitt trigger IC9 (2).
The signals delivered by gates IC9 (1) and (2) are processed by two controlled RS flip-flops
forming circuit IC14. The microprocessor IRQ interrupt is controlled by circuit IC14 outputs
using inverter IC15 (2).
The fuel flow rate variations are taken into account depending on the frequency of interrupts.
Since the frequency of transmitter signals is low, the microprocessor may perform various
operations (display control for instance) between each interrupt.
The microprocessor can authorize the reading of signals delivered by one or both
transmitters by controlling the respective RS flip-flops using monitoring circuit IC11. In the
event of simultaneous fuel flow, the microprocessor can take into account the signals
delivered by both flip-flops, by branching the output of flip-flop RS1 on the data bus via
input validation circuit IC3. Thus, the microprocessor can calculate the LH and RH fuel flow
rates according to the interrupts and data bus information.
The document reference is online, please check the correspondence between the online documentation and the printed version.
