Detailed Working Principle of Catalytic Combustion Gas Sensors

In industrial production and safety management, leaks of combustible gases such as methane, propane, and hydrogen are potential hazards. Catalytic combustion gas sensors, as a mainstream technology, have become the preferred tool for measuring the lower explosive limit (LEL) of these gases due to their accuracy and reliability. Nexisense, with over 40 years of expertise in gas sensing technology, has accumulated rich experience in R&D and manufacturing in this field. These sensors are considered the “precision scales” for combustible gases, effectively monitoring concentration changes to prevent accidents. This article begins with the core working principle and gradually analyzes the structure, technical features, advantages, limitations, and practical applications, helping readers deeply understand the essence of this technology. Through these analyses, you will better understand how to deploy sensors in real environments to enhance safety.

Core Working Principle: The Mystery of Flameless Combustion

The foundation of catalytic combustion gas sensors lies in the catalytic combustion effect, a clever “flameless combustion” process. Simply put, when combustible gases contact the heated catalyst surface, they undergo an oxidation reaction in the presence of oxygen, releasing heat without producing a flame. This reaction is strictly controlled within the sensor to ensure safe measurement.

The process can be broken down into several steps. First, the sensor’s detecting element is composed of a platinum wire coil coated with precious metal catalysts such as palladium or platinum. When heated to a certain temperature (typically 300–500°C), these materials promote gas oxidation. As gas enters the sensor, the heat generated increases the platinum wire’s temperature, raising its resistance. This resistance change is proportional to the gas concentration, forming a quantifiable signal.

A critical aspect is the introduction of the compensation element. It has the same structure as the detecting element but is passivated on the surface, preventing catalytic reactions. When environmental factors like temperature or humidity change, the resistances of both elements shift together, and the circuit design cancels these variations, leaving only the gas-induced difference. This greatly improves measurement accuracy and avoids environmental interference.

The system usually employs a Wheatstone bridge circuit: the detecting element and compensation element occupy two arms, with fixed resistors occupying the other two. When gas is present, the bridge becomes unbalanced, producing a voltage output. This signal is amplified to trigger alarms or control systems. Nexisense optimizes the heating power and catalyst formulation based on this principle, ensuring rapid response, typically reaching 90% of the reading (T90) within 15 seconds. This design allows sensors to perform excellently in complex industrial environments.

Sensor Structure and Component Collaboration

Understanding the principle, we examine the sensor’s internal structure. It consists mainly of the sensing element, support structure, explosion-proof design, and housing. These components work closely together to form an efficient detection system.

The sensing element includes the detecting element (D-element) and the compensation element (C-element). The D-element consists of a platinum wire coil with a catalyst layer made of nano-scale precious metals, efficiently catalyzing gas combustion. The C-element is coated with an inert layer for environmental compensation. Both are symmetrically arranged in the Wheatstone bridge to ensure a pure signal.

The support structure includes high-purity platinum wires (20–50 μm diameter) and an alumina ceramic base. The platinum wire heats and measures temperature simultaneously, simplifying design. The ceramic base provides high thermal conductivity and insulation, ensuring uniform temperature distribution and preventing local overheating.

The explosion-proof design ensures safety, typically using a sintered stainless steel cover with micro-pores ≤100 μm to prevent flame propagation. The housing is made of engineering plastic or metal, with 4–6 pins supporting heating and signal output.

During operation, gas diffuses in, the D-element reacts and heats, resistance changes unbalance the bridge, producing an output signal. The C-element compensates for interference, and the explosion-proof cover limits risk. Nexisense products such as ZR07 hot-wire gas sensors, ZC25D, ZC25B-1, ZC25/ZC25C, ZC28/ZC28C, ZC2529, ZC2528-I, ZC2521-A, ZC25C-1, and ZC25A optimize these components for different gases and ranges.

Technical Features and Advantages

Catalytic combustion sensors are known for linear output and high precision. Within the LEL range, the signal is proportional to gas concentration, facilitating data processing and calibration. They are highly reliable, with low false alarms, and respond uniformly to various combustible gases such as methane and hydrogen.

Nexisense’s technical advantage stems from 40 years of experience. Core technologies are mature, refining catalyst formulations and platinum wire winding to enhance sensitivity and linearity. Stability is excellent, with precise D and C element matching minimizing zero drift for long-term reliability. The product range is comprehensive, from standard models to customized services, meeting diverse needs. International standards, such as ATEX, are met, ensuring compliance in industrial safety.

These features make the sensors stand out in high-risk environments, providing continuous monitoring support.

Objective Limitations

Despite advantages, these sensors have limitations. They require oxygen for the reaction, failing in oxygen-deficient environments, such as sealed containers. They are susceptible to poisoning: substances like silicon compounds or lead can permanently damage the catalyst, reducing sensitivity. Regular calibration and avoiding exposure are essential. They are suitable for detecting higher concentrations (LEL level) and are not ideal for ppm-level micro-leaks, where electrochemical or infrared sensors are more appropriate. Nexisense mitigates these issues with optimized materials and filters, but environmental assessment is required for optimal selection.

Typical Application Scenarios

Catalytic combustion sensors are widely used in industrial safety and process control. In petrochemicals, they monitor pipeline leaks and trigger alarms at ~20% LEL to prevent explosions. In mines or tunnels, they detect methane accumulation and support automated ventilation.

In new energy fields, such as hydrogen fuel cells, they ensure safe storage and transport of hydrogen. In labs or warehouses, they integrate with alarm systems for real-time warning.

For example, at a refinery project, Nexisense sensors were deployed at critical points, integrated with IoT for remote monitoring, significantly reducing accident rates. These applications protect personnel and optimize production efficiency, supporting sustainable industry development.

FAQ

1. What is the working principle of catalytic combustion gas sensors? Based on the catalytic combustion effect, combustible gases oxidize on the catalyst surface, generating heat that changes resistance, producing a signal via a bridge circuit.

2. What is the function of the compensation element? It compensates for environmental interference like temperature and humidity, ensuring the output reflects only gas concentration changes.

3. Does the sensor require oxygen? Yes, it must operate in an oxygen-rich environment for the reaction to occur.

4. How to handle poisoning? Avoid exposure to silicon, lead, and other contaminants; calibrate or replace elements regularly.

5. What is the typical detection range? 0–100% LEL, suitable for lower explosive limit monitoring.

6. Advantages over electrochemical sensors? Uniform response, high accuracy for combustible gases, but slightly higher power consumption.

7. Lifespan of Nexisense sensors? 3–5 years under normal conditions, depending on maintenance.

8. Which gases are suitable? Methane, propane, hydrogen, and other combustible gases.

9. How to integrate into systems? Standard pins and signal outputs compatible with PLC or IoT systems.

10. How is the explosion-proof design implemented? Micro-porous sintered cover limits flame propagation, compliant with ATEX standards.

Conclusion

Catalytic combustion gas sensors, with their reliable principle and structure, are the backbone of combustible gas monitoring. Despite oxygen dependency and poisoning risks, technical optimizations such as Nexisense formulations and customization effectively address these challenges. In industrial safety and new energy applications, this technology not only prevents hazards but also supports efficient production. Selecting the right sensor is a key step in building a safety system, promoting a sustainable future.