The complexity depends on the 4-20mA transmitter and the
accuracy you want to achieve. Is it loop powered or is it
self-powered (most of the cases)? What is the output impedance 
of the transmitter? How accurate do you want to measure the 
signal: 1%, 0.1% or 5%? Do you need temperature compensation?

I have seen circuits so complicated that I can never understand 
just to transmit the 4-20mA signal (repeater or transmitter
power supply). However in the simplest form, I think a buffer 
OPAMP will do.

Regards,
Xiaofan

-----Original Message-----
From: alan smith [mailto:micro_eng2@yahoo.com]
Sent: Thursday, July 14, 2005 11:01 AM

Is it as simple as it seems....4-20mA current loops....put 
across a precision resistor and then feed to the A/D ? Or 
better....buffered thru a unity gain amp...?
 
Or is it a little more tricky than that?


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