What is the conventional range of a 4-20 mA current loop?

The range of a 4-20 mA current loop is considered conventional because it is widely used in industrial instrumentation for transmitting analog signals in process control. In this arrangement, the current signal starts at a minimum of 4 mA and goes up to a maximum of 20 mA.

The reason for starting at 4 mA instead of 0 mA is to provide a live signal that can be distinguished from a fault condition, such as a broken wire or sensor issue. When the signal is at 4 mA, it indicates that the system is operational and can reflect varying degrees of the measured variable (e.g., temperature, pressure). The additional range above 4 mA allows for a more precise interpretation of the process variable, with 20 mA typically representing the maximum measurement.

Using this conventional range also helps in reducing the effects of electrical noise and providing a better response in digital systems, since a continuous signal can be maintained across long distances with minimal distortions. This is critical in process control environments where accurate and reliable data transmission is essential.

Overall, the 4-20 mA range is a standardized approach in the industry, ensuring compatibility among various devices and systems.