Out of Dave Pierson's answer to Gary Lau: <snip> ...
there can be a significant difference between the two meters (113V vs. 120V). I'm speculating that this is due to the loaded Variac output waveform being distorted,Quite Possible. Once saw my lab instructor get fooled Real Good by similar. I Omit the details as nonTC, tho its a dandy tale of the potential pitfalls of metering...and the two meters see this differently.Just so. By Definition (and physics...) moving coil meters are _average_ responding. Scales may be marked 'RMS', however if the fine print be read: RMS ASSUMING A SINE WAVE is being measured. If not sine wave: all bets are off. Period. (Exceptions, obviously for fancy electronic, or hotwire converters, to give 'RMS'.)
.... <snip> ...a sometimes almost forgotten analog instrument is the moving iron meter, which I like to use for some simple app's, despite the somewhat lower precision and nonlinear scale: it has one big advantage: by physical principle, it's measuring the true RMS value of voltages and currents in A.C. networks with independence of their waveform....in limited frequency range. Please have a look at the following links for more info:
http://www.microtherm-international.com/upload/mediapool/ec.pdf http://www.google.ch/#hl=de&source=hp&biw=1076&bih=801&q=%09+moving+iron+instrument&btnG=Google-Suche&aq=f&aqi=&aql=&oq=%09+moving+iron+instrument&gs_rfai=&fp=4d7d8a48680024b http://nptel.iitm.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Basic%20Electrical%20Technology/pdf/L-42%28GDR%29%28ET%29%20%28%28EE%29NPTEL%29.pdf Best regards Kurt _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla