Why Do Pressure Transmitters Output Specifically 4–20mA?

Pressure transmitters, Level Transmitters, temperature transmitters and other instruments mostly adopt 4–20mA as their standard output signal. Many people wonder why the range is not 0–20mA. This set of values is not arbitrarily defined; it is an international standard formed through long-term engineering practice.

Pressure transmitters convert pressure readings into signals and transmit them to PLCs, DCS or display instruments for data acquisition and control. Compared with voltage signals, current signals feature superior anti-interference performance and are more suitable for long-distance transmission.

Industrial sites often require lengthy wiring and are subject to electromagnetic interference generated by motors, inverters, and other equipment. Voltage signals suffer voltage drops caused by line resistance, which compromises measurement accuracy. In contrast, current signals are barely affected by line resistance. As long as the load capacity of connected equipment meets requirements, signals remain stable even over long transmission distances. For this reason, current signals have become the most widely used analog signals in industrial automation.

The vast majority of pressure transmitters adopt a 2-wire design, where power supply and signal transmission share the same loop. Internal circuits of transmitters require continuous power to operate properly, so a minimum operating current must be maintained even when the measured pressure equals zero. After extensive engineering verification, the industry settled on 4mA as the zero-point current, which guarantees stable equipment operation with sufficient safety margin reserved.

In addition, the 4mA zero point enables quick equipment status diagnosis for on-site maintenance staff. A reading of 4mA indicates normal zero-pressure output, while a current drop to 0mA typically signals circuit disconnection or transmitter failure, facilitating rapid troubleshooting — another key factor behind the long-standing adoption of the 4–20mA standard.

Now that we understand why 4–20mA has become the standard signal for industrial automation, it is clear that stable and consistent output signals are critical to the entire control system.

Norhen pressure transmitters are equipped with high-performance pressure sensors and support standard 4–20mA analog output. They are fully compatible with all types of industrial control systems including PLCs, DCS and touch screens. Boasting high measurement accuracy, fast response speed, strong anti-interference capability and outstanding long-term operational stability, our transmitters offer a full range of measuring ranges, process connections and mounting options for wide application across water treatment, machinery equipment, HVAC, petrochemical, power generation and other industries.

Whether for new equipment matching or project retrofits, Norhen delivers professional pressure measurement solutions tailored to diverse working conditions. We ensure consistent, reliable 4–20mA signal transmission to safeguard industrial process control.