Jinx wrote:

> Until recently I've been using 
> 
> http://www.maxim-ic.com/appnotes.cfm/appnote_number/823 
> 
> with 4-20mA sensors, and it works very very well, on a DMM as well as
> down to the resolution of a PIC A2D. No fiddling or twiddling needed,
> unlike the op-amp designs I tried

They say there:

"The circuit performs well with 1% resistors. Monte Carlo analysis
indicates a worst-case output error of 5% due to resistance mismatch alone,
but the performance with unmatched components was better than 1% at
full-scale."

This is about what I'd expect for a typical opamp design -- the result is
mainly determined by the precision (or matching) of the resistors.

I've used the LT1637 as high-side current sensor amp with good success. One
nice feature of it is that it can have its inputs above its supply. Does it
have to be high-side? Low-side measurement is easier...

What is the fiddling and twiddling you had to do with opamp designs? After
all, in your application, the MAX472 is little more than an opamp. (It has
that absolute value output feature, but in a 4-20 mA current loop the
current direction is known.)

Gerhard

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