Main types of noise encountered in assemblies
Noise in electrical measurements

Noise can be classified into two main categories: fluctuations of statistical or quantum origin, whose characteristic times are very short compared to the measurement time, and drifts, whose characteristic times are, on the contrary, much longer. The characteristic time can be defined as the minimum time over which the noise value cancels out.

In the first case, the effects depend on the bandwidth of the measurement chain, and only the root-mean-square values of the quantities are taken into account.

In the second case, the operating frequency is of little importance (except at very low frequencies), and it's the sign and amplitude of the parasitic signals that matter.