Noise in electrical measurements

All physical observations are affected by interfering signals. For example, in a radio link, various causes can interfere with transmission (electric motors, thunderstorms, various radio transmitters, etc.). This manifests itself in the presence of unwanted, generally unpleasant sound signals: noise.

This notion can be generalized to all parasitic levels of the same nature as the useful signal. For example, astronomical observation may be hampered by city lights, which constitute optical noise.

Generally speaking, a measurement chain comprises :

• a sensor, whose function is to transform a quantity of interest (voltage, current, volume, temperature, force, speed, etc.) into an image quantity, usually electrical;

• a circuit for shaping the electrical signal (amplification, modulation, clipping, etc.);

• a transmission line ;

• a receiver, which decodes the edited image signal;

• a measurement display device;

• possibly an actuator device, controlled by the measured signal.

Throughout this chain, parasitic signals of various origins are superimposed on the signal to be measured. They may have internal causes specific to the circuit elements, or external causes such as industrial noise.