At 01:27 AM 5/13/2006 +1200, you wrote:
>Anyone have a 4-20ma loop calibrator circuit?
>
>That is a 4-20ma source and sink.
>
>I was thinking of using a AVR to do the control side but have not got my
>head around how to source / sink 4-20 ma in circuits that have different
>voltages i.e. 5v to 50v.

You make a current sink or source (your choice since it's going to look
like a two-terminal device) with sufficient compliance,
accuracy and power-handling capability for your application.

To simulate a loop-powered instrument you connect the sink/source in series
with the circuit. To source current you need an internal power supply with
sufficient voltage for all possible conditions (including the compliance of
the sink/source and the drop in your measurement circuitry) and that goes
in series with the sink/source and the load(s).

There are lots of very accurate commercial calibrators out there with lots
of features. It's cheaper to buy one than try to design one unless your
time is worth very little.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->>Test equipment, parts OLED displys http://search.ebay.com/_W0QQsassZspeff


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