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Calibrating an AC meter

Let's assume that I don't want to spend a fortune but I want to try to calibrate my AC (True RMS) voltmeter -- at least at some level of accuracy which I may never know exactly anyway but I'd really like to get within a percent or so. This precludes purchasing calibration standards and implies that I'm going to do it "on the cheap".

Let's assume I have a DC "calibration" voltage source which is manufacturer spec'd to about 5-10 PPM so I can calibrate a DC meter to a reasonable degree of accuracy.

Can I calibrate the AC meter (a Fluke 8050 "true rms" meter) using a square wave of known duty cycle and controllable frequency (so it's comfortably within the meter's band)? If so, I could create a square wave generator with CMOS logic and by measuring the high and low levels (I assume I can easily switch the circuit to a known DC state or to oscillate) and duty cycle and calculating what the RMS voltage should be? If so, then it should be "easy" to create an AC signal with known RMS voltage.

If I can't assume that making just measurements of DC voltage level and duty cycle of a square wave are sufficient to create a "calibrated" AC source, what else would I need to measure or do?

TIA Norm

Reply to
Norm Dresner
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If and only if the meter actually *measures* true RMS, as compared with the majority that measure an average and read RMS, then theoretically the waveform makes no difference, and the squaer wave is the easiest and simplist approach. However, that being said, one can determine the RMS value of a (reasonably pure) sine wave by measuring its peak accurately. One simple minded way is to use a diode and capacitor to get the peak voltage, and not load it at all when measuring; adjust a DC reference onone end of your meter with the other end being onthe capacitor (ie: the "slide-back" method). Another way is to use an operational amplifier to make an ideal diode / peak detector.

Reply to
Robert Baer

"Norm Dresner" wrote in news:FZ4td.97124$ snipped-for-privacy@bgtnsc05-news.ops.worldnet.att.net:

You ought to call some cal labs and get a price quote on calibration. Often it's not that bad if there are no repairs needed.

--
Jim Yanik
jyanik-at-kua.net
Reply to
Jim Yanik

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