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first stage of the SCU. One signal per engine (primary or secondary
sensor) is inputted into parallel tracking filters which use HP and LP
tach signals to follow the individual spools. This results in two EICAS
display readings per engine from one sensor: LP imbalance and HP
imbalance. In the event of higher than normal readings, the
secondary sensor can be selected to verify the high reading;
therefore, there will be four readouts (two per engine) which present
the degree of rotor imbalance for each spool. Each engine will have
two readouts from one sensor and the aircrew may select the
alternate sensor with the SENSOR-PRI/SEC switch located on the
cockpit overhead panel. The SCU output is 0-3 volts DC
corresponding to 0-3 inches per second of vibration in velocity units.
The EICAS will digitize these four signals and display each in digital
form.
The system also consists of a VIB MONITOR - TEST switch located
on the cockpit overhead panel. When depressed a signal of
appropriate amplitude and frequency is applied simultaneously to all
charge amplifier inputs for display by EICAS indicators. This test
function will input two units of vibration to each sensor at 120 Hz and
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-77-00
Page 3
May 31/01
Revision 4
should read 2.0 IPS on the display on all four readouts. For 2.0 IPS
display to be valid, test must be completed prior to engine start.
NOTE:
If test mode is inadvertently activated when engines
are operating, existing display will show an increase of
approximately 2.0 IPS. The press-to-test function and
display are not considered valid in this condition.
E. Engine Fuel Indication System:
(1) Engine Fuel Filter Warning:
L FUEL FILTER and R FUEL FILTER messages are provided to the
EICAS to inform the aircrew that fuel filter blockage is taking place
and that the filter element should be checked. On airplanes 1000 -
1252 not having SPZ-8400, L FUEL FILTER and R FUEL FILTER
warning lights (located on standby warning lights panel) will also
alert the aircrew to this blockage condition if standby warning light
panel switch is placed in MAN mode or in AUTO mode when EICAS
is not operational. These two warning systems are controlled by
their respective fuel differential pressure switches mounted on each
engine low pressure fuel filter. The differential pressure switch for
each side is subjected to both fuel inlet and outlet pressures and a
variation between the two pressures in excess of 7 ±0.3 PSI will
complete an electrical circuit to appropriate warning indication in
cockpit. The circuit will remain completed until differential pressure
decreases to a value approximately 1 PSI below that at which circuit
was completed.
Power from the essential 28V DC bus comes through the WARN
LTS PWR #14 and WARN LTS PWR #15 circuit breakers to the left
and right side fuel differential pressure switches, respectively. As
long as a differential pressure of less than 17 ±0.3 PSI exists across
the filter circuit to the warning system (EICAS and on airplanes 1000
- 1252 not having SPZ-8400, standby warning lights) the switch will
be open. When a filter blockage occurs and a differential pressure of
more than 7 ±0.3 PSI exists across filter, the switch will close. A
circuit will then exist to EICAS to provide L or R FUEL FILTER
readout from the essential 28V DC bus. On airplanes 1000 - 1252
not having SPZ-8400, a circuit will also exist to standby warning
lights panel L FUEL FILTER or R FUEL FILTER light if standby
warning lights panel switch is in MAN or AUTO mode and EICAS is
not operational. The circuit to these warning systems will remain
until differential pressure across the filter decreases to a value
approximately 1 PSI below the actuating point.
(2) Engine Fuel Flow Indication:
Fuel flow indication is displayed by the EICAS and the standby
engine indicator. The fuel flow transmitters are located on left side of
each engine in areas of warmer fuel temperatures, thereby
eliminating the need for specialized de-icing equipment. Each
transmitter provides an electrical signal that is directly proportional
to mass flow rate of fuel and transmits this signal to the EICAS and
the standby engine indicator.
OPERATING MANUAL
2A-77-00 PRODUCTION AIRCRAFT SYSTEMS
Page 4
May 31/01
Revision 4
Output of each transmitter is fed directly into the EICAS with signals
from the right engine fuel flow transmitter being sent to EICAS DAU
#2.
Each transmitter also sends signals to the standby engine
instrument signal conditioner to provide a digital display on the
　
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