trueRMS

trueRMS, short for true root mean square, is the true root mean square value of a voltage or current waveform. For a periodic waveform v(t) with period T, the rms value is v_rms = sqrt( (1/T) ∫_0^T [v(t)]^2 dt ). In discrete form, v_rms = sqrt( (1/N) Σ v_i^2 ). The rms value represents the effective power delivered to a purely resistive load, with P = V_rms^2 / R = I_rms^2 R.

trueRMS differs from measurements from some traditional meters that assume a sinusoidal waveform. Such meters can report incorrect values for distorted or non-sinusoidal signals. trueRMS meters compute the actual RMS for any waveform within their specified bandwidth, typically using sampling and digital signal processing to accumulate the squared values over time.

Applications include power electronics, motor drives, energy metering, audio equipment, and laboratory measurements, where signals frequently exhibit switching, PWM, rectification, or other non-sinusoidal shapes.

Limitations and considerations include bandwidth, sampling rate, and crest factor (the ratio of peak value to RMS). Signals containing frequency components outside the meter’s range or with very high crest factors can reduce accuracy. Some devices labeled as trueRMS may be accurate only for certain waveform types or frequency ranges; users should consult the device specifications.

Historical note: The concept of RMS dates to the 19th century, and the term trueRMS became common with modern digital instruments to distinguish true RMS measurement from average-responding meters.