Interfacing Onion Omega with Industrial 4-20mA Sensors The Onion Omega 2 is one of my favorite SBCs. It’s small and comes with a ton of power. There are so many neat and interesting projects that can be done with this computer. In this guide, I will show you how to use the Onion Omega with 4-20mA industrial sensors. About 4-20mA Sensors 4-20mA sensors are a powerful communication standard, commonly found in industrial applications. 4-20mA sensors use current variations to send data. Current variations can travel long distance because current does not decay over distance. Why is 4-20mA the Standard Current Range?