1, the transmission line can be easily affected by parasitic thermocouples and resistance drop and temperature drift along the wire, the transmission line can be very cheap and thinner twisted pair wire;

In 2, the current source output resistance is large enough, the magnetic field coupling to the wire loop induction voltage, will not have a significant impact, because the current minimum interference caused by the general use twisted pair can reduce interference resistance;

3, capacitance interference will lead to receiver resistance error for 4 ~ 20mA two wire loop receiver resistance is usually 250&Omega (Uout=1 ~ 5V; sampling) the resistance is too small to have a significant error, therefore, allows the wire length longer than the voltage of the telemetry system;

4, each single reading device or recording device can be changed in different channel wire of unequal length, not because of wire length caused by unequal accuracy differences; 5, 4mA for the zero level, the judgement is open or damaged sensor (0mA) is very convenient.

6, in the two line output is easy to add anti surge and lightning protection devices, is conducive to the safety of lightning protection.