6.4 Reproducibility for random vibr

6.4 Reproducibility for random vibration tests Random vibration signals are not repeatable in the time domain; no two similar length time samples from a random signal generator can be overlaid and shown to be identical. Nevertheless it is possible to make statements about the similarity of two random signals and set tolerance bands on their characteristics. It is necessary to define a random signal in a way which ensures that should the test be repeated at a later date, by a different test house or on a different item of equipment, the excitation is of a similar severity. It should be noted that all the following tolerance boundaries include instrumentation errors but exclude other errors,specifically random (statistical) errors and bias errors. The measurements are taken at the check/reference point(s).