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Title: Will 400 yc AC meter work accurately on 60 cyc? Post by: W3RSW on December 04, 2007, 12:55:40 PM I have a Triplet AC precision panel 4" x 3" Vmtr. model 430C that I've been using for years to measure filament voltage. Nothing melted including the "Shoebox" single 813 rig that I built some yrs. ago (HUZ's page) so I know it works but am not sure if its 1% accuracy is true on 60 cyc. Just found written below the face mask '400 cycles' and in handwritten india ink "1%."
So I hooked up a small 6.3 / 0.3amp fil. xfor and found the following; 7.05 volts on the Simpson reads 6.79 rms on a digital Greenlee. Now I wonder who's right, but the Greenlee does reliably read around 120 vac on my mains which has been verified by pwr. co. - uh, huh, yeah assuming they have accurate voltmeters. Is there a formula that might apply here assuming the diff. is due to going from 400cyc to 60 and not an innaccurate meter? Don't tell me it's V * (400/400-60) or 'cos' this or 'sin' that.... heh, heh. Better yet, Oh I know, it's (7.05 - 6.79) * V ;) Title: Re: Will 400 yc AC meter work accurately on 60 cyc? Post by: Tom WA3KLR on December 04, 2007, 01:13:19 PM Hi Rick,
It may or it may not! Do you have a function generator to play with? Some of those meters just have a rectifier and resistor and rely on the mass of the movement for averaging. I think most AC meters with a filter capacitor presume a sine wave, peak detect and calibrate for the r.m.s. equivalent for sine. The RCA Senior VoltOhmyst has this spec: +/- 1 dB 30 Hz to 3 MHz. If you have this circuit, it may have been designed for 400 Hz and you may be below the cut-off. If your panel meter is just the rectifier and resistor, the final decider is whether the movement may resonate at 60 Hz and show a noticeable width of vibration. I think the calibration would stay the same with this type of meter though. You could add your own filter cap. if possible and re-calibrate. My 2 cents worth. Title: Re: Will 400 yc AC meter work accurately on 60 cyc? Post by: Tom WA3KLR on December 04, 2007, 06:55:01 PM My Fluke multimeter is my most trusted meter.
Title: Re: Will 400 yc AC meter work accurately on 60 cyc? Post by: W3RSW on December 04, 2007, 08:46:43 PM Yeah, that's what I need.... a Fluke. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
Maybe I'll be lucky and find a 'fluke' farm out label inside the Greenlee. fwiw the meter shows no oscillation at 60cps so must have some sort of filtering. Then again, the eye records a blur at much over 15cps. Movies and TV, etc. I think I'll delicately open it up to see. But this has to be a clean room process. Just got done cutting and filing a steel control shaft in the rig room so I know there a lot of iron filings jus' a'waitin' to literally jump inside my meter works. Did that one time in my rushed youth and trashed a really good meter. |