Basic concept of 4-20mA analog transmission performed by instruments in industrial processes.
The left is a mock instrument measuring part of a process and transmitting a 4-20mA signal over a "loop". On the right the transmitted 4-20mA is converted to voltage for sampling, digitization, storage, monitoring, controls, or whatever.
Added 3 ohms or resistance to the communication wire. It's about 2.5 ohm, give or take, for 1000 feet of 14AWG.
*the relay is only for simulation convergence. Not to be confused with the concept outlined above.
