Kai,

What you show is excellent with one major exception

You can NOT reference 4-20 to ground. The 4-20mA system (concocted by someone whose fanclub I am not a member of) allow theoritically any number of devices in series on the signal line. It is not uncommon to see a 4-20 line with a 'generator' an 'indicator' and a 'control unit' in series. Also, once I had a problem where someone had installed readouts all over the factory and eventually exceeded the capability of the 'generator'.

HOWEVER, as far as I can see your schematic will work just fine after the ground connections are removed, I would, based on experience, use +-15V for the op-amps to gain a larger common mode capability.

Erik