The most common instrument used to measure the effective (RMS) value of any type of wave, including non-sinusoidal waves, is an RMS (Root Mean Square) meter or voltmeter. An RMS meter is designed to calculate the effective value of a waveform by averaging the squares of the instantaneous values of the waveform over a specific time period and then taking the square root of the result.
The reason an RMS meter is suitable for measuring effective values of any type of wave is that the effective value represents the equivalent heating effect or power associated with the waveform. It is the value that would produce the same amount of heat or deliver the same amount of power as a steady direct current (DC) value. Since the heating effect or power calculation involves the square of the instantaneous values, the RMS meter provides an accurate measure of the effective value by accounting for both positive and negative peaks of the waveform.
The RMS meter can handle various types of waveforms, including sinusoidal waves, square waves, triangular waves, and complex waveforms, because it utilizes the same mathematical principle for all of them. It effectively calculates the average power or heating effect over time, irrespective of the shape or nature of the waveform.
It's worth noting that if the waveform is not periodic or the frequency content is not within the measurement range of the RMS meter, other techniques or instruments might be required to accurately measure the effective value. However, for a wide range of practical applications involving periodic or non-sinusoidal waveforms, an RMS meter is a versatile and commonly used instrument.