What does a 4-20 mA signal represent?

A 4-20 mA signal is widely recognized as an analog current signal utilized for transmitting process variables within industrial control systems. This is the standard convention for many types of sensor outputs and control systems because it allows for a clear, linear representation of measured variables.

The 4 mA indicates the lowest point of the measurable range, while 20 mA signifies the upper limit. This range provides a "live zero" feature, meaning that a 4 mA signal not only indicates the absence of a signal but also confirms that the circuit is active, which is important for detecting faults like cable breaks. The current loop can transmit data over relatively long distances without significant loss of signal integrity, making it highly reliable for industrial applications.

This approach is especially beneficial in environments where electromagnetic interference might distort signal quality, as the 4-20 mA signal is less prone to such disturbances compared to voltage signals. The use of current as the transmission medium also contributes to safety and efficiency in control systems.