PERFORMANCE MAINTENANCE PAGE COMPACTED EICAS DISPLAY A AORB
Engine Vibration Indication Figure 2
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A. Functional Description
(1)
The (AVM) signal conditioners are powered from the 115 volt ac busses 3 (for engines 1 and 2 - M118) and 4 (for engines 3 and 4 -M7846).
(2)
The pieozoelectric accelerometer on each engine senses engine vibration in the radial direction and generates electrical signals proportional to engine acceleration.
(3)
The signal conditioners receive N1, N2, and accelerometer charge signals. The signal conditioner converts the charge signal to a voltage signal proportional to the velocity of the engine vibration. The signal is then converted to a digital signal for use by the digital signal processing (DSP) unit.
(4)
The AVM signal conditioner uses the accelerometer signal in conjunction with the N1 and N2 tachometer speed signals to determine the vibration level caused by each rotor (N1 and N2). Software then compares the rotor vibration to determine which signal (N1 or N2 rotor) is to be input to the EIU's as a function of worst case, or highest vibration.
(5)
The rotor of highest vibration is shown for each engine on the auxiliary EICAS display. If either speed sense is lost, EICAS shows broad band (BB) for that engine. Vibration readings for each rotor and a broad band reading are shown on the performance maintenance page of the EICAS.
DM7198A CH A
CH B DM7198B CH B
CH A
DM7353
M7198 ELECTRONIC EEC SPEED
ENGINE CONTROL TRANSDUCER (N1)
M7353 EIU-LEFT CH B
DM7352
CH A
T1519 EEC ALTERNATOR (N2 TRANSDUCER) M7352 EIU-CENTER
DM7351 DT677DM118M7351 EIU-RIGHT
E2-6 EIU RACK
T677 ACCELEROMETER M118 AVM SIGNAL ENG 2
SAME AS ENG 1115V AC CONDITIONER ENG 1&2 ENG 1
BUS 3
VIB AMP
ENG 1&2
NOTE: ENGINES 1 AND 2 SHOWN; ENGINES 3 AND 4 SIMILAR. P6 MAIN POWER DISTRIBUTION PANEL
Airborne Vibration Monitoring (AVM) System Simplified Schematic
Figure 3
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////////////////////////A / PW4000 SERIES /747-400 / ENGINES/MAINTENANCE MANUAL ////////////////////////
(6) AIRPLANES WITH VIBRO-METER S362A001 AVM SIGNAL CONDITIONERS; A 3 line, 8 character per line LED display on the AVM front panel will give the fault history.
(a)
The AVM's Built-In test Equipment (BITE) will give the fault history.
(b)
Push and release one of the four buttons on the front panel of the AVM signal conditioner to do a self test of the AVM signal conditioner. Only the AVM signal conditioner is tested. The procedure to do a self test of the AVM signal conditioner is given in the adjustment/test (AMM 77-31-00/501).
(c)
The procedure to read the fault history is given in the maintenance practices (AMM 77-31-00/201).
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