I've used the MAX4173 for high-side current measurement;

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1971

Nigel



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
>
> Unfortunately a new design means a revamp, and the MAX472 is
> not recommended for new designs. Sigh
>
> The client found the RCV420
>
> http://focus.ti.com/docs/prod/folders/print/rcv420.html
>
> but it's relatively expensive (from where I can get them)
>
> I found this, the INA138 - (231kB)
>
> http://focus.ti.com/lit/ds/symlink/ina138.pdf
>
> It looks similar, a little simpler even, but nowhere in the ANs does
> it say suitable for 4-20mA. It seems to me it could do it
>
> Googling around finds several devices, just wondering whether
> anyone has a proven cheap accurate method for 4-20mA before
> I go ordering parts
>
> TIA
>
>   

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