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(e) Phase Angle Lag: If the low pressure rotor is not balanced, the vibration analyzer will give its angular location. The phase angle lag is the angle between the actual location of the unbalance and the location the analyzer shows.
NOTE: This procedure uses phase measurement equipment that
____ measures from the N1 speed pulse to the vibration pulse (maximum). Measure positive angles, in this coordinate system, in the opposite direction from the direction in which the engine turns. Some phase measurement equipment, such as the MTI equipment, measure positive angles in the direction in which the engine turns (lead angle).
(f)
Phase Angle: The angle between the signal from the vibration transducer and the signal from the N1 speed reference. The speed reference is given once per revolution.
(g)
Sensitivity: The moment weight that causes 1.0 mil (0.025 mm) of vibration.
(h)
Once Per Revolution N1 Speed Reference: Once every revolution a signal is received by the N1 speed transducer. The short tooth of the tachometer gear on the turbine shaft coupling makes the signal. As an alternative procedure, use an optical tachometer for the once per revolution N1 speed reference.
(i)
N1 Reference Blade: Fan blade with an ink mark to identify the short tooth location.
(j)
Stable Vibration: A Stable Vibration is a vibration of which the vibration maximum does not change by more than one-fourth of the average vibration during 30 seconds of the engine operation.
(k)
Vibration Survey: To do a test and write the engine vibration data against the rotational speed during an engine acceleration or deceleration. This finds which engine speeds give the maximum vibration levels which are not permitted.
(l)
Trim Balance Survey: To do a test and write the vibration amplitude and phase angle data of the low rotor. The vibration amplitude is measured while the engine is stable at the peak vibration level. You can then calculate the correct weight.
B.
Equipment
(1)
MTI 8900-6714 Engine Selector Switch Box,
Mechanical Technology Inc.,
968 Albany-Shaker Road,
Latham, NY 12110
(2)
MTI 8115-6713 PBS Jumper Cable,
Mechanical Technology
(3)
MTI 8900-5065 AVM Interface Cable, Mechanical Technology
(4)
MTI 7000-4133 Portable Balancing System - PBS-4100 ( This includes a Computer and Data Acquisition Unit (DAU), Mechanical Technology
(5)
PWA 85306 Puller - Pratt & Whitney
(6)
PWA 85307 Puller - Knocker, Pratt & Whitney
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