AC True RMS Measurement

"When measuring the value of an alternating current signal it is often necessary to convert the signal into a direct current signal of equivalent value (known as the root mean square, RMS value). This process can be quite complex (see root mean square for a detailed mathematical explanation). Most low cost instrumentation and signal converters (for example handheld multimeters of the sort used by maintenance engineers) carry out this conversion by filtering the signal into an average value and applying a correction factor.

The value of the correction factor applied is only correct if the input signal is sinusoidal. The true RMS value is actually proportional to the square-root of the average of the square of the curve, and not to the average of the absolute value of the curve. For any given waveform, the ratio of these two averages will be constant and, as most measurements are carried out on what are (nominally) sine waves, the correction factor assumes this waveform; but any distortion or offsets will lead to errors. Although in most cases this produces adequate results, a correct conversion or the measurement of non sine wave values, requires a more complex and costly converter, known as a True RMS converter."

http://en.wikipedia.org/wiki/True_RMS_converter

GA to you.

However, there are some pitfalls apparently, as humorously explained here....

http://www.scribd.com/doc/33402767/True-Rms-Not

Dear Solar Eagle

GA for you thank you.