Use a fixed voltage as your supply or exciter voltage.  24 V seems to be
standard.  Then calculate the resistance value to get a current flow of
20mA.  Read the voltage drop across the resistor.  The drop will vary
according to the current drain.  Your transducer should be in line with
the resistor and the other end of your supply voltage.  That is the current
to voltage converter portion of your circuit.  The use a 4046 P.L.L. for
a V.C.O. and read the freq on your PIC.

Brent

Brent Pollock
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At 05:17 PM 10/28/96 +0200, you wrote:
>I'd appreciate some ideas on a precision, temperature-stable current
>to voltage circuit to convert e.g. a 4-20mA signal to a 0-5V signal
>(which I will then feed into a Voltage-to-freq converter and read
>with a uP).
>
>Many thanks
>Rob Bruce-Brand
>Durban Electricity
>