# BERAN

## Proven Condition Monitoring Solutions # Glossary

• ## Harmonics

In addition to the fundamental frequency of a vibration there are also superimposed additional frequencies at 2x, 3x, 4x etc in theory all the way to infinity! The 2nd harmonic is one octave higher at twice the frequency. Middle ‘C’ on a piano is at 261.626 Hz.

• ## Hertz

One ‘cycle per second’ is often termed one ‘Hertz’ after the German physicist. Standard scientific prefixes are used so 1000 cycles per second is 1000 Hertz (1000 Hz) or 1 kiloHertz (1kHz).

• ## Integration

In vibration analysis Integration is the mathematical procedure which is used to convert an Acceleration (ins/sec/sec) signal into a Velocity (ins/sec) and inturn Velocity into Displacement (ins). The reverse of this procedure is differentiation.

• ## Lines on an FFT

An FFT resolves the input accelerometer signal into a number of discrete lines or bins. The larger the number of lines the greater is the detail and clarity of information that can be extracted. For example a typical 0 to 500Hz FFT analysis, at a resolution of 200 will sample the signal and produce one lines for all frequencies between 0 Hz and 2.5 Hz, and another for frequencies between 2.5 Hz and 5.0 Hz etc. (500 / 200 = 2.5). This may be satisfactory for some circumstances. However if it is known that in the aircraft there are gears, shafts or other components which are generating frequencies closer than 2.5 Hz then it may be impossible to identify them correctly. This will necessitate using a higher 400, 800 or even 6,400 'line' resolution.

• ## Mils

Mils is a measure of vibration displacement, where 1 Mil is equal to one thousandth of an inch. It should not be confused with metric millimetres.

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