jnorv Posted March 30, 2003 Share Posted March 30, 2003 As a mechanical engineer, when I took the required EE courses 40 years ago I slept thru most of them, but I seem to remember that AC voltmeters are not linear over wide frequency bands. Just how big a problem is this considering the audio range. Will most modest cost AC volt meter be good enough up to 20 Khz? Jim N Quote Link to comment Share on other sites More sharing options...
mike stehr Posted March 30, 2003 Share Posted March 30, 2003 Can't really answer your question, but I do plan on getting a old HP tube AC voltmeter in a couple of weeks. They have uses. Quote Link to comment Share on other sites More sharing options...
Andy W Posted March 31, 2003 Share Posted March 31, 2003 I had to answer this question one day in the lab. I have a Fluke 87 True RMS DMM. For a comparison, I used a Tektronix TDS 210, 60MHZ scope. The problem with DMM's is that they can be inaccurate at high frequencies, as you know. The signal in question was a somewhat squarish wave from a switch mode power supply running at 65kHz, and I needed to know the RMS voltage. The duty cycle was not 50%, and the positive and negative amplitudes were not equal. Using the scope's RMS measurement function, I found the RMS voltage. Then using the DMM, I measured the AC voltage and then the DC voltage. Using the equation Vrms=sqrt(Vac^2+Vdc^2) I calculated what the DMM thought was the RMS voltage. To my surprise, it was within a few percent of the scope's measured value. I knew the Fluke was good, I didn't know it was THAT good. ~$350, add ~$50 for calibration certificate. -Andy W Quote Link to comment Share on other sites More sharing options...
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