My return to Classic Cmp - San Diego, software archive, etc.
ard at p850ug1.demon.co.uk
Mon Dec 15 16:21:57 CST 2008
> And before that, very early digital voltmeters...
How did they work? I rmember seeing (and alas failing to obtain) an
partically mechanical digital voltmeter. The circuitry was a servo
system, similar to the ones used in chart recorders. The motor drove a
mechanicla turns counter, coupled to an accurate multi-turn helical
potentiometer, which provided the feedback to the servo amplifier (it
replaced the slidewire in th chart recorder implementation). THe
operation is obvious, apply an input voltage, the motor turns until the
feedback from the pot balances the input votlage, the turns counter then
effectively shows where the pot is
Somewhere I have most of a valved DVM. 'Most of' because alas some idiot
stripped a number of passive components off it before I got it. It's
stuffed with valves (I would guess about 50 of them), including 4
trochotron counter tubes. The display is a row of nixie tubes. I've not
figured out how it worked, alas.
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