Understanding AC Waveform Ratios

The question asks to identify the term used for the ratio of the maximum value to the RMS value of an AC waveform. Let's look at the definitions of the factors provided in the options.

Defining Key Electrical Factors

• Form Factor: The form factor of an alternating quantity (like voltage or current) is defined as the ratio of its RMS value to its average value.

  \(\text{Form Factor} = \frac{\text{RMS Value}}{\text{Average Value}}\)

• Crest Factor: The crest factor, also known as the peak factor or amplitude factor, is defined as the ratio of the peak (maximum) value to the RMS value of an alternating quantity.

  \(\text{Crest Factor} = \frac{\text{Maximum Value (Peak Value)}}{\text{RMS Value}}\)

• Diversity Factor: Diversity factor is a concept used in power systems. It is defined as the ratio of the sum of individual maximum demands of various subdivisions of a system to the maximum demand of the whole system. It is not a characteristic of a single waveform's shape.

  \(\text{Diversity Factor} = \frac{\text{Sum of Individual Maximum Demands}}{\text{Maximum Demand of Whole System}}\)

• Average Factor: While we often use the 'Average Value' of a waveform, 'Average factor' is not a standard technical term commonly used in this context for waveform ratios like form factor or crest factor.

Identifying the Ratio of Maximum Value to RMS Value

Based on the definitions, the ratio of maximum value / RMS value is precisely the definition of the Crest factor. The crest factor gives an idea of the peaks that the waveform reaches relative to its effective (RMS) value. For a pure sine wave, the maximum value is \(\sqrt{2}\) times the RMS value, so the crest factor for a sine wave is \(\frac{\sqrt{2} \times \text{RMS}}{\text{RMS}} = \sqrt{2} \approx 1.414\).

Therefore, the ratio of maximum value/rms value is known as the Crest factor.