Turbine Rear Frame Vibration Sensor Figure 003
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Turbine Rear Frame Vibration Sensor Figure 004
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Aft Avionics Compartment
Figure 005
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Electrical Diagram
Figure 006
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- the DMU
- and printer (if installed) for maintenance purposes.
B. Description
(Ref. Fig. 007)
The signal conditioner is composed of :
- 1 power supply module
- 2 channel modules
- 1 balancing module
- 1 data processing module These modules are removable parts from the signal conditioner and are repairable subassemblies.
(1) Channel module Each channel module processes the signals from the two engine accelerometers and from the two speed signals N1 and N2 : this enables extraction from the overall vibration signal, of a component due to rotor first order unbalance. Only one accelerometer is used at any particular time. The second accelerometer is selected manually via MCDU 'ACC. RECONFIGURATION menu' or automatically at the next power up due to a failure of the N1 BEARING ACCEL. The N1 and N2 signals are used :
- to drive the tracking filters, and
- slave their center frequencies at the shaft rotational speed. The accelerometer signals pass through these tracking filters which extract the N1 and N2 related fundamental vibration. The acceleration signal is then integrated in order to express the vibration in velocity terms.
(2) Balancing module
The balancing module receives :
- the accelerometer signal
- the N1 signal including the 1/REV synchronisation pulse. The balance module uses these information to compute the position and the amplitude of the unbalanced signal.
(3) Data processing module
This module manages under program control, the whole signal
conditioner operation.
The data processing module :
- receives the necessary inputs from the CFDS
- provides outputs to the aircraft corresponding to the selected mode
(the outputs depend on the aircraft status).
Two modes are available :
- the normal mode
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EVMU Block Diagram
Figure 007
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- the MENU mode, used on the ground for maintenance purposes (Ref. paragraph Operation).
(4) Power supply module The power supply module receives the 115VAC/400Hz power. It provides the other modules with the necessary voltages.
C. Power Supply (Ref. Fig. 006) The EVMU is supplied with 115V/400Hz by busbar 101XPA, through circuit breaker 1EV. The maximum power consumption is less than 30VA. The EVMU is not affected by power loss up to 5 ms. For power interrupt time between 5 ms and 20ms, the equipment does not supply any inadvertent indication. It returns to normal operation 200 ms after power return.
D. Operation
The EVMU provides the following functions :
(1) Actual vibration level Measurement of the actual vibration velocity corresponding to acceleration signals filtered with narrow band filter slaved to rotor speeds. As normal vibration is depending on rotor speed an absolute actual level cannot give a correct vibration indication : so for each speed, the EVMU processes the ratio actual value/maxi value. This ratio is multiplied by 10 and is available on the EVMU output for display.
- N1 vibrations are measured as a displacement in mils (1/1000 of an
inch), while N2 vibrtions are measured as a speed in ips (inch per
second). N1 phase angle is also measured in degrees for balancing
purposes.
- MAX N1 narrow band vib selection and normalization for display: the
display between 0 and 5 units depicts a vibration between 0 and 5
mils (linear).
(Ref. Fig. 008)
- MAX N2 narrow band vib selection and normalization for display: the
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