William K. Borsum wrote:
>
> At 11:16 AM 6/3/99 -0600, you wrote:
> >Modulate the DC maybe....FSK like ?
> >
> >Suppose I have a situation where I want to send power and control
> >signals to a device. Suppose too that I want to do this all with
> >2 wires (power and return). Is it at all feasible to send the data
> >on top of the power line, and have it separated at the destination?
>
> There are a number of companies doing this on top of 4-20 mA control and
> signal loops.  There is even a standard to cover the protocol--uses
> standard FSK signals on a high frequency carrier.  Simple capacitive
> coupling at either end, and the frequency is high enough to not interfere
> with the "DC" level process signals.
>
> Check out the magazine "control engineering"--I think they have a web page
> too.  The name "HART" comes to mind for the protocol, but I wouldn't swear
> to it.
>
> ****************************************************************************
> ********
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> text.
> William K. Borsum, P.E.
> OEM Dataloggers and Instrumentation Systems
> <borsum@dascor.com> & <www.dascor.com>

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