Will 400 yc AC meter work accurately on 60 cyc?

[W3RSW]

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       

[Tom WA3KLR]

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.

[Tom WA3KLR]

My Fluke multimeter is my most trusted meter.

[W3RSW]

Yeah, that's what I need.... a Fluke.
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.