Normally, the transmitter can be wired into 2-wire or 4-wire system. In 4-wire system, we separate it into 2 set of 2 wires, first set, we use for archive the electrical signal output and second set, we use for DC supply. In 4-wire system, if the plant and control room are very far so we have to use a lot of wires, it causes increasing in cost. 2-wire system is created for decreasing the cost of wire, it combines the DC supply and electrical signal into only 2-wire to save the cost. The electrical signal we archive from transmitter is current signal. If we want to convert the current signal into voltage signal for some devices, the resistor is used for this condition. The value of the resistor depends on the current output from transmitter and voltage signal we need. The diagrams of 2-wire and 4-wire system for 4-20 mA current standard signals convert to 1-5 voltage standard signals are shown below.