Lexicon RMS

Abbreviation for the English term "Root Mean Square".

The term is used in connection with alternating voltages or currents. An alternating voltage changes continuously between two extreme values, in the simplest case in the form of a sine curve. In many cases, you want to know what the voltage would be of a constant signal that produces the same power in the load as the AC voltage signal. In other words, which produces the same effect in terms of energy transfer.

Example: The nominal voltage of the usual AC mains in every household is 230V. This voltage is the RMS (or root mean square) value, because an incandescent lamp would shine with the same brightness if it were supplied with direct current of 230V. In reality, however, the mains voltage changes between about -325V and +325V in the form of a sine wave.

Accordingly, the RMS value gives a kind of average, but related to the power. It is the voltage that results in the same power (averaged over time).

See also:

• Wikipedia article: RMS