What exactly is the difference between the 4-20 mA output signal in 2- and 3-wire technology? Bargain is answered best from the viewpoint of an individual: An output signal in 2-wire technology means:
less wiring required
better EMC protection, since interferences could be filtered more easily
better protection against wiring errors
The only advantage of 3-wire technology is that higher ohmic loads are possible, i.e., the existing loop may also be operated on a measuring instrument of relatively high input impedance. Conclusion: With the exception of a high ohmic load requirement, 4-20 mA in 2-wire technology offers the user clear advantages- also over other signals, such as for example 0-10 V.