Forrest,
The typical isolation schemes apply such as pulse transformers and
opto-couplers. The HCPL-3120 is an opto-coupler that has one emitter and two
photo transistors. One is used on the sending side as feedback to compensate
for non-linearity (which WILL be present in any "linear" device) It will
have significant latency no matter how you do it. Other methods involve
digital coupling using voltage to frequency converters and optocouplers or
pulse transformers.
--
Martin K

On 3/26/07, Forrest W. Christian <forrestc@imach.com> wrote:
>
> I'm currently working on a remote telemetry project.   One of the
> requirements is the ability to measure various DC (and possibly AC)
> voltages.   These may be above or below ground, ground referenced, or
> not.   I do have some flexibility with specifying what inputs are
> permitted (voltage), but don't have enough flexibility to say that "all
> signals must be ground referenced and must not be negative in reference
> to ground".  (Actually I might be able to do this, but I'm not going to
> be happy about it long term).
>
> Oh yeah, I'm not thrilled about the prospect of needing a negative
> (below ground) power supply to do this since this is a cost sensitive
> application.  But if I must, I do realize that I could do this with some
> sort of level shifting opamp - but that isn't really the way I'd like to
> do this.
>
> External adc's are not out of the question if needed...
>
> What I'd love is a dirt cheap completely isolated adc, but I realize
> that this isn't going to happen.
>
> Ideas?
>
> -forrest
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