very simple circuit to interface a current loop sensor to an input which is designed for a voltage
http://www.4qdtec.com/curli.html
Uses a low-current-drain MAX4073H amplifier to sense the current flowing through a 4- to 20-mA loop.
http://www.e-insite.net/ednmag/index.asp?layout=article&articleid=CA154820
http://www.e-insite.net/ednmag/index.asp?layout=article&stt=000&articleid=CA289969&pubdate=4%2F17%2F2003&spacedesc=designideas
Describes a three IC, 4-20 mA process current, digital-to-analog converter
http://www.analog.com/UploadedFiles/Application_Notes/266329066AN21.pdf
The current loop can be sourcing or sinking and can be referenced to either the power-supply V+ or ground.
http://www.ti.com/sc/docs/psheets/abstract/apps/sboa023.htm
conversion circuit between 0-20mA and 0-10V interface
http://users.swing.be/gonzague.colpaert/circuits.html
http://www.bb-elec.com/tech_articles/current_loop_app_note/not_digital_current_loop.asp#42