What is 4-20mA Current Loop?

What is a 4-20mA Current Loop?

4-20mA (Current Loop) is an analog signal standard that uses electric current instead of voltage to transmit sensor data. It has been a staple of the industry since the 1950s and can be considered the "English of automation".

• 4mA: Represents the lowest value of the measurement range (0%) (Not zero, but "live zero").
• 20mA: Represents the highest value of the measurement range (100%).

Why 4-20mA instead of 0-10V?

Voltage signals (0-10V) suffer from voltage drop over long distances due to cable resistance. For example, a signal leaving the source as 10V might drop to 9.5V after 100 meters, resulting in a huge 5% measurement error.

Current signals, however, are constant throughout the loop according to Kirchhoff's law. Whether the cable is 1 meter or 1000 meters, 4mA is 4mA at every point. additionally, the 4mA level is used as "live zero"; meaning if the wire breaks, the current drops to 0mA, and the system immediately recognizes a fault (wire break).

Amazeng GDT Digital Transmitters can read 4-20mA sensors and convert them to digital data, or operate as a 4-20mA output simulator themselves.