Editing Amplitude (section)

===Root mean square amplitude===
{{Further|Root mean square#In common waveforms{{!}}RMS of common waveforms}}

[[Root mean square]] (RMS) amplitude is used especially in [[electrical engineering]]: the RMS is defined as the [[square root]] of the [[mean]] over time of the square of the vertical distance of the graph from the rest state;<ref>Department of Communicative Disorders [[University of Wisconsin–Madison]]. ''[http://www.comdis.wisc.edu/vcd202/rms.html RMS Amplitude] {{Webarchive|url=https://web.archive.org/web/20130911063155/http://www.comdis.wisc.edu/vcd202/rms.html |date=2013-09-11 }}''. Retrieved 2008-08-22.</ref>
i.e. the RMS of the AC waveform (with no [[DC component]]).

For complicated waveforms, especially non-repeating signals like noise, the RMS amplitude is usually used because it is both unambiguous and has physical significance. For example, the ''average'' [[power (physics)|power]] transmitted by an acoustic or [[electromagnetic wave]] or by an electrical signal is proportional to the square of the RMS amplitude (and not, in general, to the square of the peak amplitude).<ref>Ward, ''Electrical Engineering Science'', pp. 141–142, McGraw-Hill, 1971.</ref>

For [[alternating current]] [[electric power]], the  universal practice is to specify RMS values of a sinusoidal waveform. One property of root mean square voltages and currents is that they produce the same heating effect as a [[direct current]] in a given resistance.

The peak-to-peak value is used, for example, when choosing rectifiers for power supplies, or when estimating the maximum voltage that insulation must withstand. Some common [[voltmeter]]s are calibrated for RMS amplitude, but respond to the average value of a rectified waveform. Many digital voltmeters and all moving coil meters are in this category. The RMS calibration is only correct for a sine wave input since the ratio between peak, average and RMS values is dependent on [[waveform]]. If the wave shape being measured is greatly different from a sine wave, the relationship between RMS and average value changes. True RMS-responding meters were used in [[radio frequency]] measurements, where instruments measured the heating effect in a resistor to measure a current. The advent of [[microprocessor]]-controlled meters capable of calculating RMS by [[Sampling (signal processing)|sampling]] the waveform has made true RMS measurement commonplace.