(2) Measurement of the unbalance data The EVMU measures the position and the amplitude of the rotor unbalance of each engine. It provides these information to the output bus when available.

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R R  N1 Vibration Display Figure 008
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R R  N2 Vibration Display Figure 009
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 (3) Computation of the advisory level The advisory level is equal to the lower value of the two following limits : Limit 1 = Max value - X with

 - Max value being the maximum vibration levels which can occur on the engine. These values are depending on the rotor speeds

 - X being the margin to the Max value = 4U for N1 and 5.7U for N2
 Limit 2 = A + K. Initial value with

 - A = Minimum normal vibration value = 2U for N1 and 1.3U for N2

 - K = scale factor = 1

 - the initial value is defined in paragraph (4)
 The advisory level is permanently compared with the actual level. If
 the advisory level is reached, a digital information is sent to the
 ECAM.

R **ON A/C 051-051,

R (4) Initial value storage
R The initial value is the actual value when the engine is new or
R rebalanced. At each engine serial number corresponds an initial
R value.
R The initial value is stored in the equipment :
R - either automatically after request to the MCDU
R - or point by point from the FCDU keyboard.
R An initial value is defined every 5 percent of RPM :
R - from 20 percent to 125 percent for N1 vibration
R - from 50 percent to 125 percent for N2 vibration.
R When stored, the initial values are taken into account for advisory
R calculation (Limit 2).

R **ON A/C ALL

R (5) Frequency analysis The EVMU can do a frequency analysis if requested from the MCDU on the ground. The EVMU does the analysis at a selected N1 or N2 speed and uses any valid accelerometer. The maximum frequency analysis is 500 Hz and the frequency increment between adjacent spectral lines is 4 Hz.
R (6) Storage of unbalance data If requested, the system can store the balancing data during the cruise phase at five predetermined different engine speeds.
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R (7) BITE maintenance and fault information The equipment contains a BITE to detect internal and external failure. Complete description of the BITE system is given in 31-30-00. During the execution of the cyclic BITE sequence, the following parts of the EVMU are checked :
 - the non-volatile memory

 - the timers

 - the analog-to-digital converter

 - the ARINC 429 transmitter and receivers

 - the real tacho generators.
 During the power-up sequence of the BITE, the following parts of the
 EVMU system are checked :

 - N1 and N2 NB velocity

 - unbalance data

 - N1 and N2 tacho frequencies

 - accelerometer signals.
 Any detected failure is stored in the non-volatile memory with GMT,
 date and other reference parameters.

 E. Interfaces
 (1) Inputs
 The receives analog signals from :

 - the 4 engine accelerometers (2 per engine)

 - the N1 and N2 speed sensors from each engine.
 All these signals are described in the dedicated sensor description.
 The EVMU also receives digital signals from CFDS and printer through
 ARINC 429 data bus. These signals are described in the dedicated
 interface description.

 (2) Outputs The EVMU transmits output signals through an ARINC 429 data bus. The data transmitted on the single low speed line is in conformity with ARINC 429. The SDI definition is as follows :
　
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