Radiation

[John Honniball]

Tony Duell wrote:
> 'A potentiometer-wire voltmeter is better than a DMM because the former 
> draws no curret at balance'. This is more subtle. While it's true that a 
> potentiometer-wire voltmeter dwraws no curret at balance, you can never 
> know it's exactly at balance. You are limited by the sensitivity of the 
> detector you're using. And when that detector is a moving coil/pointer 
> (not a mirror) type of meter with a sensitivity of, perhaps, 1uA if 
> you're lucky, then a 10M ohm DMM actually takes less current from, say, a 
> Weston standard cell.

I heard that argument for the superiority of the potentiometer at
school, too.  It would've been in about 1979.  Wish I'd thought of
the counter-argument about the sensitivity of the meter, but I
didn't think of it until many years later.

-- 
John Honniball
coredump at gifford.co.uk