The measurement Laser beam and the reflected Laser beam are made to interfere on the photo detector creating a fringe pattern. An optical sensor system OFV-505 detects the changes in the fringe pattern and generates optical interference signal which is fed to the decoders. Decoders generate an analog signal in relation to this input optical interference signal.

Measurement of damping

A quantitative measure of damping factor is obtained by using the half-power bandwidth method shown graphically in Figure 37.1.

Figure 37.1 Damping measurement using 3dB method

The damping factor, can be determined by

(37.1)

is determined from the half power points down from the resonant peak value, X_max. On a decibel scale, this corresponds to –3dB down from the peak value. Hence, is also referred as 3 dB method .