4. Diagnostic tools

4.1 RC (constant resolution) or FFT (fast Fourier transform) spectrum and zoom

It's a representation of vibration amplitude in acceleration on a linear frequency axis. With current technology, its resolution is generally 400 lines. The spectrum obtained will therefore be a curve passing through 400 points evenly spaced in frequency.

The frequency band is defined prior to on-site measurements. A distinction is made between :

• LF spectra (low frequencies [0-50 Hz]) ;

• MF spectra (medium frequencies [0-500 Hz]) ;

• HF spectra (high frequencies [0-10,000 Hz]) ;

• high-resolution zoom [f ₁ ...