Why Are 4-20mA Pressure Transmitters the Most Commonly Used?

In industrial automation applications, pressure transmitters are available with various output methods, including voltage, digital, and current outputs. Among them, 4-20mA has remained mainstream for many years. This is not simply due to industry convention; rather, it achieves an excellent balance among stability, transmission capability, interference resistance, and system compatibility.

In applications such as chemical processing, water treatment, HVAC, energy, and equipment manufacturing, pressure transmitters often need to transmit signals over long distances while dealing with electromagnetic interference from motors, variable-frequency drives, and relays. In such situations, the advantages of 4-20mA output become more evident, which is why it has become a standard solution.

First, Understand a Key Question: Why Not 0-20mA?

When many people first encounter pressure transmitters, they ask a common question: Since it is a current signal, why not use 0-20mA instead of starting at 4mA? The answer is quite practical. The 4mA signal not only represents the lower range limit but also serves as a “live signal” indication.

When a pressure transmitter outputs 4mA, the system knows that the device is at or near the zero point or lower limit, while the loop itself is operating normally. If the signal drops to 0mA, the control system will usually identify it first as a broken wire, power failure, or fault, rather than assuming that the process pressure is actually zero.

What may appear to be merely a 4mA “margin” actually greatly improves fault-diagnosis efficiency. For continuous production systems, the ability to quickly identify line abnormalities is often more important than simply measuring a value.

Five Main Reasons Why Pressure Transmitters Use 4-20mA

1. Stronger Interference Resistance

The most common problem in industrial environments is not whether the sensor can measure, but whether the signal can be transmitted back stably. If a pressure transmitter uses voltage output, changes in line resistance, external noise, and grounding conditions can all have a significant impact.

By contrast, 4-20mA is a current signal, and its primary basis for evaluation is the current level, making it less susceptible to distortion caused by voltage drops in the wires. This is particularly important at sites with long cables, numerous devices, and complex environmental conditions.

2. Suitable for Long-Distance Transmission

Many pressure transmitters are not installed next to the control cabinet. Instead, they are distributed across storage tanks, pipelines, pump stations, heat-exchange systems, and even outdoor equipment. As the transmission distance increases, voltage signals are more likely to attenuate, and accuracy may fluctuate accordingly.

4-20mA loops are better suited to these operating conditions. As long as the power supply and load are properly matched, the pressure transmitter can send measurement results stably to a PLC, DCS, or display instrument, reducing the need for intermediate compensation and complex commissioning.

3. High Compatibility and Easier System Integration

Based on current industry applications, 4-20mA remains a standard input method supported by a large number of control systems. PLC analog input modules, secondary instruments, recorders, and remote data-acquisition terminals can generally receive this type of signal directly.

This means that when 4-20mA pressure transmitters are selected, system integration is less complicated, and replacing older equipment is more straightforward. For project owners, having to make fewer program changes, interface modifications, and additional conversions is itself a highly practical benefit.

4. Enables Two-Wire Wiring

Many pressure transmitters use a two-wire design, in which power supply and signal share the same pair of wires. The benefits are very direct: simpler wiring, less installation work, and a lower probability of wiring errors.

For systems with numerous measurement points, such as building piping networks, industrial water treatment systems, and complete equipment packages, wiring costs are not insignificant. With a 4-20mA two-wire pressure transmitter, overall installation efficiency is higher, and subsequent maintenance is more convenient.

5. Facilitates Fault Alarms and Status Determination

A standardized current range makes it easier for pressure transmitters to establish unified evaluation logic with host systems. For example, abnormal ranges below 3.8mA or above 20.5mA can often be configured as fault alarms, over-range indications, or loop-abnormality alerts.

This type of mechanism is highly practical in continuous monitoring applications. It does more than simply “measure pressure”; it also helps the system determine equipment status and improves the controllability of the entire automation chain.

Performance of 4-20mA Pressure Transmitters in Practical Applications

In water supply systems, pressure transmitters are usually installed at pump outlets, main pipelines, and pressure-stabilizing equipment. Since equipment starts and stops frequently at these sites and motor interference is significant, 4-20mA output can provide more stable feedback on changes in pipeline pressure, facilitating coordinated control.

In chemical and process industries, pressure transmitters face more complex operating conditions. In addition to long transmission distances, they may also need to meet requirements for explosion protection, corrosion resistance, temperature drift, and continuous operation. In such cases, the maturity and compatibility of 4-20mA can significantly reduce system risks.

In equipment integration applications, many manufacturers also give priority to 4-20mA pressure transmitters. The reason is simple: different customers may use different control platforms, but current-type interfaces are generally universal, making standardized delivery easier.

Not Every Application Requires 4-20mA

It should be noted that 4-20mA being the most commonly used option does not mean it is suitable for every project. If the transmission distance is very short, on-site interference is limited, and the system is designed for high-speed data acquisition, 0-5V, 0-10V, or digital communication methods may also have their own applications.

For example, some laboratory equipment places greater emphasis on response speed and local control, while some intelligent systems need to read more status data simultaneously. In such cases, a pressure transmitter with a communication protocol may be more suitable. The key to selection is not blindly following a single solution, but determining whether it matches the operating conditions and interface requirements.

What to Focus on When Selecting a 4-20mA Pressure Transmitter

Once 4-20mA output has been selected, price should not be the only consideration. The stability of a pressure transmitter often depends on fundamental parameters such as measurement range, accuracy class, overload capacity, supply voltage range, media compatibility, and temperature characteristics.

1. First, confirm that the measurement range covers actual pressure fluctuations and retains a reasonable margin.
2. Then verify the output type and determine whether it is a two-wire 4-20mA output or another combined output.
3. Check the power supply and load conditions to prevent insufficient loop drive capability or abnormal signals.
4. Pay attention to the installation interface, sealing method, and compatibility of the materials with the measured medium.
5. If the environment is complex, also evaluate the ingress protection rating, explosion-protection requirements, and vibration resistance.

Furthermore, a good pressure transmitter must not only be “usable”; it must also maintain consistency during long-term operation. This is particularly important on continuous production lines, where a single measurement deviation may affect subsequent control logic.

From a Product Capability Perspective, Stable Output Matters More Than a Single Parameter

For pressure transmitter manufacturers, 4-20mA is only an output format. The factors that truly determine application performance are the sensing element, compensation technology, production consistency, and calibration process. Only when these fundamental capabilities are solid can the advantages of the standard signal be fully realized.

Xi'an Shenghongchuang Instrumentation Co., Ltd. has long focused on pressure sensors, pressure transmitters, and various industrial measurement and control products. In terms of industrial-site adaptation, product stability, and supporting delivery, the company can provide solution support that is better aligned with the actual requirements of different operating conditions.

Conclusion

The widespread use of 4-20mA in pressure transmitters is essentially because it is better suited to the real-world conditions of industrial environments. Its overall performance in interference resistance, long-distance transmission, system compatibility, fault identification, and wiring efficiency has enabled it to maintain its mainstream position over the long term.

If you are evaluating pressure transmitter options, you can begin with the output method, operating conditions, and control system interface. After clarifying these basic requirements, selecting a suitable 4-20mA pressure transmitter will make the selection process more reliable and subsequent operation easier.