The current allowed by the transmitter is called the loop current and it is proportional to the parameter that is being measured. In Figure 1, current supplied from the power supply flows through the wire to the transmitter and the transmitter regulates the current flow within the loop. The two “Rwire” symbols represent the resistance of the wires running out to the sensors and back to the power supply (Power supply means IO cards or barriers).

A receiver resistor that converts the current signal to a voltage.

Basics of 4-20mA Current Loopįigure 1 shows a schematic of the simplest 4-20 mA current loop.

The signaling current is not affected by these voltage drops as long as the power supply voltage is greater than the sum of the voltage drops around the loop at the maximum signaling current of 20 mA. In a 4-20 mA current loop, all the signaling current flows through all components the same current flows even if the wire terminations are less than perfect.Īll the components in the loop drop voltage due to the signaling current flowing through them. Current loops are ideal for data transmission because of their inherent insensitivity to electrical noise.

The 4-20 mA current loop is a very robust sensor signaling standard.

Multisim 12 impedance meter