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>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.
>
>Is there a reference to a standard for 4-20ma testing?

Shouldn't be too hard to do a transistor with a suitable emitter resistor
for the current desired, while the base is fed from a reference voltage. I
know guys here have used that system for putting known currents through
thermistors.

Know change the reference voltage to a suitable DAC, and you should have
something suitable. Without knowing just how accurate you want the known
current, you may be able to use a PWM to drive it, in which case you would
get away with a smalllish 16F series, maybe the top end 12F, depending on
how you talk to it to adjust the current.


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