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We had a requirement to measure the RMS value of a unipolar square wave being fed to a resistive load. Our resistive loads were light bulb filaments (Numitrons) so the degree of brightness was dependent on the applied RMS.
Our digital multimeters did not have an RMS measurement capability, but they could measure the average value of the waveform at hand.
Conversion of a measured average value to the RMS value was accomplished by taking the average value and dividing that by the square root of the waveform’s duty cycle.
The applicable equations are shown in Figure 1.
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Figure 1 Equations used to convert a measured average value to RMS value by taking the average value and dividing that by the square root of the waveform’s duty cycle.
John Dunn is an electronics consultant, and a graduate of The Polytechnic Institute of Brooklyn (BSEE) and of New York University (MSEE).
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