My return to Classic Cmp - San Diego, software archive, etc.

[Tony Duell]

[NLS's products]

> 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.

-tony