Signals & Analog
4-20 mA
Definition
The standard analog signal in process control: a current between 4 and 20 milliamps, where 4 mA is 0% of the calibrated range and 20 mA is 100%.
Current is used because it is constant everywhere in a series loop, so wire resistance does not change the reading the way it changes a voltage signal.
The 4 mA live zero is what makes a broken wire detectable: 0 mA is not a valid measurement, so it means the loop is open.
Also known as: current loop, analog loop, 4 to 20 milliamp.
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