Question: what is the difference between 2 wire and 4 wire?
Answer: 2-Wire vs. 4-Wire: A 4-wire transmitter is either powered by a 110V or 220V power supply. This allows direct activation of relays, pumps, solenoids, etc. ... A 2-wire transmitter is loop-powered, which means it is powered by a low voltage, low current, DC power supply, typically 24V.