NDIR or catalytic？How to find a Combustible Gas Sensor？

There are so many benefits of infrared combustible gas sensors in applications in the oil and gas industry that it seems as if infrared sensors are the perfect choice, and there are even some misconceptions that catalytic combustion sensors may be on their way out.

There are undeniable benefits of infrared technology for detecting combustible gases compared to the industry standard catalytic combustion technology: its ability to detect gases in oxygen-deficient environments, its immunity to substances like silicone and sulphur that can affect catalyst performance, and the elimination of the need for frequent calibrations. However, the limitations of infrared sensors are also undeniable.

The limitations of infrared sensors are mainly due to the fact that they do not respond to all combustible gases.

For example, infrared combustible gas sensors cannot detect hydrogen (H₂). If an infrared sensor is used to detect combustible gases, the user may not be protected when hydrogen is present in the environment. 

The limitations of infrared sensors are not only in hydrogen detection, but their ability to detect gases is limited by the ability of the target gas to absorb infrared light. Some kinds of combustible gases cannot be detected by infrared combustible gas sensors, such as acetylene, acrylonitrile, aniline and carbon disulphide and so on.

What are the advantages of catalytic combustion sensors?

The main advantage of catalytic combustion sensors is the detection of combustible gases by combustion. As a result, catalytic combustion sensors are capable of detecting almost any combustible gas. The response of catalytic combustion sensors to combustible gases is essentially linear, with a close correlation between the response of different types of combustible gases and the calibration gases, and most combustible gases have a response factor of less than 2. The response of infrared sensors is non-linear, and only becomes linear when the sensor is designed to target a specific gas. Response factors vary greatly from gas to gas and in some cases may exceed 10. If a gas with a response factor of ≥10 is encountered, the instrument will give a false alarm when the actual gas concentration is only 1 per cent of the lower explosive limit.

Compared with infrared sensors, catalytic combustion sensors are less affected by environmental factors such as temperature and pressure, as these environmental factors can significantly impact the performance of infrared sensors. Therefore, if accurate and reliable detection is desired from infrared combustible gas sensors, calibration settings need to be performed in similar environments.

There is no denying the fact that infrared technology has irreplaceable advantages for detecting combustible gases in certain applications. However, before moving away from the long-standing catalytic combustion technology, make sure that your application matches the technical characteristics of the sensor. Otherwise, the risks you face may far outweigh the rewards.