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(d) A solution on a graph (with a one-shot plot procedure and, if it is necessary, vector analysis, and intervectorial analysis) can also be used to calculate the correction weight and position. 1) To do the one shot plot procedure, a phase angle matrix (a
table that shows the relation of the phase angle to the balance screw locations at specified rotor speeds) must be made (as shown in the subsequent task: Phase Angle Matrix Determination).
NOTE: This procedure, which will correct most imbalances,
____
is only tried one time.
a) It is not possible to make one phase angle matrix to apply to all systems, because each trim balance system operates differently and has differently related phase angles.
2) The vector analysis has these steps: a) The phase angle and imbalance quantity of the first operation of the engine is found.
b) The phase angle and imbalance quantity of a subsequent operation of the engine (that is done with added correction weights) is found.
c) With the vectorial analysis, the two pairs of numbers are compared to find the accurate phase lag and sensitivity values.
d) A more accurate position and quantity of weight that is necessary to trim balance (decrease the imbalance) is then found.
3) The intervectorial analysis, which is used when the vector analysis does not correct the vibration problem, has these steps.
4) The phase lag and sensitivity values are calculated again.
5) A vibration improvement is done on the data to find an "optimum weight and location".
(3) The data that follows is necessary to do the analyzer procedure:
(a) A vibration signal from the FAN vibration sensor is transmitted through a signal conditioner (charge amplifier) to a trim balance analyzer. The FAN sensor is an accelerometer with a sensitivity of 100 pC/g.
NOTE: If the internal No. 1 bearing accelerometer does not
____ operate, an alternative accelerometer can be installed on the FFCCV (Fan Frame Compressor Case Vertical) location (AMM 77-31-01). The alternative accelerometer also has a sensitivity of 100 pC/g.
If the alternate accelerometer is used, a trim balance limit of 3.5 mils DA must be obeyed.
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CFM56 ENGINES
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(b) A vibration signal from the TRF (turbine rear frame) vibration sensor is transmitted through the signal conditioner (charge amplifier) to the trim balance analyzer. The TRF accelerometer has a sensitivity of 50 pC/g.
NOTE: TRF sensors with a 50 pc/g sensitivity have an
____ identification (white) bushing installed on the sensor lead approximately 3 inches (76 mm) from the connector mounting bracket.
(c) A speed signal from the N1 speed sensor is transmitted to the trim balance analyzer. (In some analyzer systems the speed signal is transmitted to the signal conditioner). 1) The speed sensor gets fan rotor input from a 30 tooth wheel
attached to the fan rotor. One tooth on this wheel is thicker than the others. Each time this tooth goes near the sensor, a special signal is transmitted. The analyzer uses this signal to calculate the phase angle that is related to the imbalance indication.
(4) The three shot plot procedure, which is used when there is no
equipment available to find the phase angle of the imbalance, has
the steps that follow:
(a)
The quantity of the initial imbalance is found.
(b)
This initial quantity is compared with the quantities of the imbalances caused by a test weights which are put at three locations, which are apart by 120 degrees.
(c)
The data is then put on a graph to find the position and quantity of weight necessary for the last trim balance.
(d)
The three shot plot procedure uses a breaker/cable selector switch. 1) This switch divides the vibration signals from the No. 1
bearing sensor (or the alternative, fan frame compressor case vertical (FFCCV) sensor) and the turbine rear frame (TRF) sensor.
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