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B. The engine accelerometer uses piezoelectric crystals to sense and transmit engine vibration information to the AVM signal conditioner. The piezoelectric crystals are stacked with an inertial mass. When the engine vibrates, the inertial mass tends to stay at rest causing the crystals to be alternately squeezed and released. This produces an electric charge that varies in proportion to the radial acceleration of the unbalanced rotor. Metallic collectors receive this charge which is then transmitted to the AVM signal conditioner. The accelerometer and electrical cable are shielded to prevent externally induced signals.
3. Signal Conditioner for the Airborne Vibration Monitoring (AVM) (Fig. 1)
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A. There are two signal conditioner units for the AVM installed in the electrical and electronics rack. One is installed on the E1-1 shelf, for engines 1 and 2 (M118), and one is installed on the E2-1, for engines 3 and 4 (M7846).
B. The signal conditioners receive vibration signals from the engine accelerometers, N1 signals from the EEC speed transducers and N2 signals from the EEC alternators. The vibration signals are processed and transmitted to the EIU's for display on EICAS.
C. Input signals and output data are available through a connector on the front panel of the unit. This allows system tests without disconnecting the airplane system.
4. Indication (Fig. 2)
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A. Engine vibration parameters are shown on the auxiliary EICAS display directly below the oil quantity display. The engine vibration indication includes the vibration actual readout, vibration actual pointer, and vibration mode message (N1, N2, or BB).
B. A white number adjacent to the vertical scale gives a digital indication of engine vibration. The readout shows engine vibration in units from 0 to 5. 5 units is equal to:
-10 mils da for N1
-2.5 ips for N2
-5.0 ips for broad band
C. Actual engine vibration is shown on a vertical analog scale. A white triangular shaped pointer on the inside of each vertical scale gives the actual rotor vibration indication.
D. A white N1 or N2 shows above the actual readout and identifies the rotor with the highest vibration. Broad band (BB) replaces N1 or N2 if a speed input is missing.
E. N1 vibration, N2 vibration, broad band vibration, and the phase angle of the N1 rotor unbalance are shown on the performance maintenance page of the EICAS.
F. In the compacted EICAS display, N1, N2, or BB vibration data is shown in digital form only. For more information on vibration indication, refer to Integrated Display System, AMM 31-61-00/001.
5. Operation (Fig. 3)
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////////////////////////A / PW4000 SERIES /747-400 / ENGINES /MAINTENANCE MANUAL ////////////////////////
78 21 81
N2 X-BLD
17.6 17.6 FF 0.0 18.3
OIL P 65 65 12 66
OIL T 105 105 103 107
SEE B
15 15 OIL Q 19 15 SEEA N2
N2 N2 N2
1.2
1.2 VIB 0.5
1.2
AUXILIARY EICAS DISPLAY A
PERFORMANCE TAT +21c D-T0 1 +23c CABIN ALTITUDE
GROSS WT287.6 1.83 1.83 REV 1.83 AUTOTHROT DISC
SAT +12.0 CAS 245 TAT+12.0 1.62 1.62 1.00 1.65 OUTFLOW VLV L
GS 245.6 MACH0.615 ALT21030
EPR (11 LINES)
OIL
70 70 PRESS 70 70 1.800 1.800 EPR MAX1.800 1.800
80 80 TEMP 80 80 1.7531.753 EPRCMD 1.7531.753 CON IGNITION
SEATBELTS
18 18 QTY 18 18 1.7531.753 EPR 1.7531.753 75.6 75.6 N1 15.2 83.7 RECALL STATUS PG 1
85.6 85.6 1N 85.6 85.6 TAI 250 246-324 KTSFL
1.3 1.2 1.3 1.2 2 1 VIB N N 1.3 1.2 1.3 1.2 350 75.3 765 75.3 2N EGT 350 75.3 350 75.3 587 17.6 78 587 17.6 78 2N FF EGT 0.0 21 97 623 18.3 15 XB 535 81 GEAR DN UP DN UP
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