4-20mA Sensors and 0-20mA Current Transmitters

4-20mA sensors and 0-20mA current transmitters are used in industrial automation and control systems to provide proportional measurements for a range of environmental factors including temperature, flow rates, pressure, tank level depths and more, over long distances that can be read by a connected environmental monitoring unit, PLC or RTU.

4-20mA sensors are ideal for transmitting proportional analog measurements over long distances as they are less affected by electrical noise than traditional sensor. A 0-20mA sensor may require a second power soure to create the measurement circuit.

How 0-20mA and 4-20mA Sensors Provide Measurements

The sensors have mimumum and maximum values of 0-20 and 4-20 and provide a proportional electrical current representing the values measured to a connected monitoring base unit or PLC. For example for a 4-20mA sensor, 4 represents the 0% and 20 represents 100%; therefore a 12mA measurement would be 50%.

The Differences Between 0-20mA and 4-20mA Sensors

0-20mA and 4-20mA Sensors have different output ranges and their characteristics can affect which is the most appropritate to choose for a particular industrial automation and monitoring application.

0–20mA: for this sensor the lowest possible measured value is 0mA and the highest is 20mA

4–20mA: for this sensor the lowest possible measured value is 4mA and the highest is 20mA

Aside from different measurement ranges, the major distinction between the two is how they handle the zero-point signal.

0–20mA: as 0mA is within the operational range of the sensor and the minimum measured value, it can be difficult to identify if the sensor has become disconnected or malfunctioned

4–20mA: with the 4-20mA sensor, there is no 0mA measurement and so this value represents a disconnected or broken sensor or fault in the detection system and so the 4-20mA sensor can provide more reliable data and fault detection

With a 4-20mA sensor the 4mA baseline provides power to the sensor itself (loop powering), removing the need for a separate power source and current signals are less susceptible to electrical noise (EMI) and voltage drops over long cable runs (u to 1000m). The sensor is widely used in industrial applications including oil & gas, process control and manufacturing.

Please contact our Projects Team if you need any further information.