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Look at data radios for 4-20ma conversion to RF and back to 4-20. Phoenix Contact is a starting point. Can you recommend others?

You can use a DGH D1251C 4-20mA input module with three wire RS-232 connection to connect to a data radio. It will digitize and transmit 4-20mA values. Then you can use a DGH D4261 on the receiving end to convert RS-232 data from a modem back to 4-20mA.

There is an similar example in datasheet on link below:

http://www.dghcorp.com/datasheets/dgh_d34.pdf

Have a look at Elpro

http://www.elprotech.com/

Steve
www.mtlblog.com

Also take a look at FreeWave (http://www.freewave.com). The FGR-IO Series. We are a distributor for them them and they have been great to work with. Look for a distributor in your area/industry.

I'm sure there are others out there but FreeWave and Phoenix Contact are the ones I am familiar with.

joe