Even usiong the dual opto method you will need to supply power to the isolated side to drive the opamps etc. that do the linearising. I played with this type of thing a few years ago but was unable to get satisfactory offset drift with temperature & device variations - although my requirement was very tight. (better than 20uV drift) My reccommendation is to provide the isolation at the digital level - either using optos or GMR isolators. (NVE IL715 etc devices). Richard P Wouter van Ooijen wrote: > > > But I want to avoid needing a power source at the 4-20mA side. -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu