A 4 to 20 mA analogue output is a common industrial signal used to transmit measurement values from a sensor to a controller or monitoring device. The current represents the measurement range, with 4 mA as the zero point and 20 mA as the full scale value.
This signal is popular because it is accurate, resistant to electrical noise, and can be transmitted over long distances without losing quality. It also interfaces easily with controllers, indicators, and recorders.
The 4 to 20 mA output is widely used in process control and automation to transmit values such as temperature, pressure, flow, and level.