RMS, or root-mean-squared, is a method of getting the true value of an AC signal. It’s also known as the heating value; in other words, the value that corresponds to the heating effect of a voltage. RMS has other applications; for example, the speeds of molecules in a gas may be calculated using the temperature and mass of the molecules. But it is in electronics measurements that it finds its primary use.

Most cheap multimeters, and all analog meters, read the average value of an AC signal and correct it to the RMS value on the scale. This works fine for a sinusoidal signal, but can be way off for other signal waveforms, especially complex ones.

A true-RMS converter will convert the value of an AC waveform — of any type — to the corresponding DC value in real time. In my youth, we would look at the specifications of audio amplifiers and scoff at anything that did not give an RMS power rating. With RMS values, you know what you’re getting none of this ephemeral peak power or mu...