Agilent Make Better RMS Measurements with Your DMM - Application Note 5988-6916EN c20140723 [9] free download

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Keysight Technologies Make Better RMS Measurements with Your Digital Multimeter Application Note Introduction If you use a digital multimeter (DMM) for AC voltage measurements, it is important to know if your meter is giving you peak value, average value, root-mean-square (rms) value, or something else. If the answer is "something else," you may be in trouble, and the trouble usually happens with rms measurements. This application note will help you understand the different techniques DMMs use to measure rms values, how the signal affects the quality of your measurements, and how to avoid common measurement mistakes. 2011 NCSL International Workshop and Symposium 03 | Keysight | Make Better RMS Measurements with Your Digital Multimeter - Application Note Measuring RMS Measuring rms values is more responding or average-responding Two measurement challenges are complicated than it appears at meters rely on these scaling factors. associated with high crest factors. first glance. If it is complicated, The first involves input range. why do we bother? Because The scaling factors apply only to Imagine a pulse train with a very true rms is the only AC voltage pure sine waves. For every other low duty cycle but a relatively high reading that does not depend on type of signal, using this approach peak amplitude. Signals like this the shape of the signal. It often is produces misleading answers. If force the meter to simultaneously the most useful measurement for you are using a meter that is not measure a high peak value and a real-world waveforms. really designed for the task, you much lower rms value, possibly easily can end up with significant creating overload problems on the Often, rms is described as a measure error--as high as 40 percent or high end and resolution problems of equivalent heating value, with more--depending on the meter on the low end. a relationship to the amount of and the signal. power dissipated by a resistive The second challenge is the load driven by the equivalent DC The ratio of Vpk to Vrms known as amount of higher-frequency value. For example, a 1Vpk sine the crest factor, is important to energy in the signal. In general, wave will deliver the same power measurement accuracy. The crest high crest