The significance of distortion and crest factors in AC measurements

The uncertainty of any AC measurement is increased when the signal departs from a perfect sine wave. Depending on the nature of the distortion, it may be convenient to examine the problem in the frequency or time domain. When a waveform is distorted from the ideal sine form, harmonics are present. These can be identified and quantified by carrying out a Fourier analysis of the waveform. The consequences of harmonic content can be evaluated using the above expressions. A selection of results for typical levels of individual harmonics is given. It is emphasised that rms value is much less influenced by harmonic content than other measurements. The effects of active circuits are discussed pointing out that exact details of the source are important