Difference between 2 wire and 4 wire level transmitter?

what is the difference between the 2 wire level transmitter and 4 wire level transmitter?

AnsIn case of 4 wire transmitter, 2 wire is used to give power to the transmitter and other 2 wire to transmit the signal. In case of 2 wire , the 2 wire carries the power as well as the signal. Example- 4 to 20 mA is flowing through the 2 wire and according to level the current is changing.