At 10:31 AM 10/28/99 -0600, you wrote:
>>I'm working on a data logger which is a little different than what I've
>>done before.
>
><snip>
>
>>
>>Now my question:
>>
>>How do I hook these separate analog signals up without sharing the ground
>>with the Power circuit?
>>

This is similar to a problem I was just working on.  We were measuring
current loops, so we could power the isolated side of the circuit.  I'm not
sure if that's an option for you here.  What we did is basically just power
an AD off of the current loop via a zener and send the serial signals
through optoisolators.

Some of the other things we thought about are :
1: analog optoisolators ....  really crappy temp coefficient kills your
accuracy over temp.
2: Voltage to frequency using op-amps then through opto isolators or caps.
Uses a fair amount of power on the iso side.  This problem can be solved by
having a truly isolated supply on the other side using a transformer.
3: A sort of charge sharing setup where storage caps are switched from iso
circuit to internal circuit.  I never quite got this one, but the EE's tell
me it should work.
4: Voltage to PWM through opto-isolators.  Also somewhat of a power hog and
sort of complicated.

HTH

-Erik Reikes