Jinx wrote:
>> Think solar site where the instrument is powered from the same
>> batteries that you are measuring voltage from
> 
> Can you do anything about that ?
> 

No, unfortunately.

This will typically be used at remote solar-powered sites.   In fact, 
almost every one of these will be powered by solar power and will be 
expected to measure at least battery voltage, solar array voltage, 
charging current and load current.  And, because the only source of 
power is the battery array, this will be powered by the battery array.

If I was *only* monitoring the batteries, that would be easy, but the 
other big piece of this is to monitor things like fuel tank levels, 
generator operational status, signal strengths, etc. - all of which are 
designed by different companies, and some make the assumption that 
you'll be using a normal, isolated, voltmeter to do the measurements, 
and as such do weird things like drive the signal below their ground, or 
use a negative reference voltage, etc.

-forrest
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