OK, didn't know if you had any example circuits to share, its been about 5 years since I've done a 4-20mA interface, and that one was a controlled environment where I didnt have to worry about the source, and I just used a shunt across the opamp.

--- On Mon, 1/18/10, Xiaofan Chen <xiaofanc@gmail.com> wrote:

> From: Xiaofan Chen <xiaofanc@gmail.com>
> Subject: Re: [EE] analog / current loop
> To: "Microcontroller discussion list - Public." <piclist@mit.edu>
> Date: Monday, January 18, 2010, 7:02 AM
> On Mon, Jan 18, 2010 at 10:21 PM,
> alan smith <micro_eng2@yahoo.com>
> wrote:
> > What do you suggest using for protection? Just a zener
> to
> > clamp the voltage across the sense resistor?
> 
> If you do that, make sure your zener is protected. There
> might be
> some IC based protection scheme (from Maxim?). Or you can
> use
> a PTC together with some over-voltage protection circuits.
> 
> 
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> Xiaofan http://mcuee.blogspot.com
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