Detailed Output Signals of Electrochemical Gas Sensors

Electrochemical gas sensors play a key role in detecting toxic and hazardous gases, where the output signal directly determines measurement accuracy, transmission reliability, and integration convenience. With over 40 years of experience, Nexisense has extensive expertise in signal processing for electrochemical sensors. This article explains the essence of the output signal, its generation mechanism, common conversion forms, technical characteristics, and selection recommendations, helping engineers and users understand this crucial aspect and choose the right output type for their projects. By understanding these principles, you can fully leverage electrochemical sensors in industrial safety, environmental monitoring, and portable devices.

Essence of the Output Signal: Weak Current

The core output of an electrochemical gas sensor is an electric current. This current arises from oxidation or reduction reactions of the target gas at the sensor electrode: gas molecules diffuse to the electrode, react with the electrolyte and catalyst, and generate an electron flow proportional to gas concentration.

This relationship can be expressed as: I ∝ C, where I is the current and C is the gas concentration. The actual current is extremely small, usually in the nA (nanoampere) to μA (microampere) range. For example, a typical carbon monoxide sensor produces 50–300 nA per 1 ppm CO. This weak signal reflects the sensor's high sensitivity but poses challenges: noise, temperature drift, and transmission attenuation can affect its usability.

Therefore, in most practical applications, the raw current is not used directly. It is amplified, filtered, and converted through built-in or external circuits to form standardized outputs. Nexisense optimizes electrode materials, electrolyte formulations, and front-end amplifiers to ensure low-noise, stable base currents for reliable downstream processing.

Common Output Forms in Practice

After processing, the raw current is mainly converted into analog voltage or analog current outputs, with some advanced models supporting digital interfaces.

Analog Voltage Output

The simplest and most cost-effective method converts current to voltage using a high-precision load resistor: V = I × R. Typical resistor values range from 10 kΩ to 100 kΩ, adjusted for the desired voltage range. The voltage signal is linear to gas concentration, commonly 0–3 V or 0–5 V corresponding to 0–full scale.

Advantages include simple circuitry and direct compatibility with most microcontrollers (e.g., Arduino, STM32), suitable for portable detectors, lab instruments, and small integration projects. The drawback is lower interference resistance; long-distance transmission (>tens of meters) can be affected by electromagnetic noise and line resistance. Nexisense modules like the MQ-E3 basic version provide this output for rapid prototyping.

Analog Current Output (4-20mA Loop)

The 4-20mA current loop is the most widely used standard in industrial sites:

• 4 mA corresponds to zero (0% FS or no gas)

• 20 mA corresponds to full scale (100% concentration)

• Currents

  <3.5 ma="" or="">21 mA indicate faults (e.g., disconnection, short circuit)

The current loop is highly interference-resistant: even with line resistance changes or hundreds of meters distance, the current remains stable. It supports two-wire power and signal sharing, ideal for petrochemical, environmental, and metallurgical industrial environments. Nexisense gas transmitters like the TX310 series adopt this output with precision current sources, ensuring linearity and long-term stability.

Digital Output

With IoT and digitalization trends, more electrochemical sensors support RS485, Modbus RTU, or I²C interfaces. These provide data validation, remote configuration, and multi-sensor networking, suitable for smart factories and environmental monitoring stations.

Nexisense Signal Processing Advantages

Nexisense electrochemical sensors offer key advantages in signal output:

• Stable base current: High-purity electrodes and optimized electrolyte reduce background current and noise, minimizing zero drift and ensuring reproducibility.

• Excellent linearity: Output remains proportional to concentration across the full range, simplifying field calibration.

  
  

• Variety of options:

• Raw sensor modules: Weak current or analog voltage output for OEM circuit design.

• Complete gas transmitters: 4-20mA or RS485 industrial signals, plug-and-play.

Products cover gases like CO, H₂, SO₂, formaldehyde, NH₃. Typical models include MQ-E3-SO2, MQ-E3VG-H-01/02, TX310-G801, TX310-H07/H630, TX310-R08 series.

Selection and Application Recommendations

Output selection depends on application:

• Portable/handheld devices: analog voltage for low power and simple integration.

• Fixed industrial monitoring: 4-20mA for long-distance, interference-resistant transmission.

• IoT/remote monitoring: digital RS485/Modbus transmitters for PLC, SCADA, or cloud integration.

Installation tips:

• Avoid strong electromagnetic interference near wiring.

• Calibrate zero and full scale every 6–12 months.

• For long-distance 4-20mA lines, use shielded twisted pair cables.

Nexisense supports customized output range, response time, and interface protocols to meet project requirements.

FAQ

1. What is the raw output of an electrochemical sensor? A weak current proportional to gas concentration, usually nA to μA.

2. Why not use the raw current directly? It is too weak, susceptible to noise and transmission loss, requiring amplification and conversion.

3. When is analog voltage output suitable? Short-distance transmission, portable devices, and direct microcontroller reading.

4. Advantages of 4-20mA loop? Strong interference resistance, long-distance transmission, fault detection, industrial standard.

5. What do 4 mA and 20 mA represent? 4 mA = zero gas, 20 mA = full scale.

6. What does current below 4 mA indicate? Faults like sensor failure, disconnection, or power issues.

7. Does Nexisense support digital output? Yes, some transmitters provide RS485/Modbus RTU for networking.

8. How is linearity ensured? High-quality electrodes, optimized electrolyte, and precision amplifiers.

9. How to handle signal noise? Use low-noise op-amps, filters, and optimized PCB layout.

10. How to choose output type? Portable = voltage, industrial fixed = 4-20mA, digital = RS485.

Conclusion

Electrochemical gas sensor output starts as a weak current and, through careful amplification and conversion, forms reliable voltage, 4-20mA, or digital outputs, meeting diverse needs from lab to industrial sites. Nexisense continuously optimizes signal stability and linearity, offering complete solutions from raw modules to full transmitters. Choosing a stable, adaptable sensor output enhances measurement accuracy and ensures long-term reliable operation, making signal interface selection a critical step for project success.