SENSORS
The 4–20 mA current loop
A process value is represented by a current between 4 and 20 mA.
INTERACTIVE EXAMPLESIMULATION
The principle
In a common linear scale, 4 mA represents 0% and 20 mA represents 100% of the configured range. The transmitter regulates loop current; supply voltage and load must be suitable. A 4 mA live zero helps distinguish a zero reading from an open loop.
An example
Move the process value between 0 and 100% and see how I = 4 + 16 × fraction sets the current in mA.
Important
A value below 4 mA does not automatically indicate a particular fault. Error levels and tolerances depend on the equipment and configuration.