Infrared (IR) Sensors

How IR Sensors Work

Infrared (IR) sensors detect gas concentrations by measuring the absorption of infrared light at specific wavelengths. An infrared light beam passes through the gas and reaches the collection optics, which splits the beam and directs it through filters onto IR detectors.

• The measuring beam (around 3.3 μm) is absorbed by gases like hydrocarbons, reducing its intensity.
• The reference beam (around 3.0 μm) is unaffected and reaches the detector at full strength.

By comparing the intensity of the two beams, the IR sensor determines the concentration of the target gas, typically expressed as a percentage of the lower explosive limit (LEL).

• Accuracy

IR sensors provide excellent accuracy when detecting gases like hydrocarbons and carbon dioxide. Their performance remains stable even in low-oxygen environments, which would disable pellistor sensors. However, calibration to the specific gas type being detected is critical to maintaining accuracy, especially when multiple gas types are present. Unlike pellistor sensors, IR sensors are immune to poisoning by chemicals such as sulphur or lead, making them more durable in certain applications.

• Reliability

IR sensors are highly reliable in detecting gases in environments where catalytic sensors may fail, such as in oxygen-depleted atmospheres or areas with high concentrations of interfering gases. Additionally, IR sensors are not susceptible to poisoning or “sooting” from hydrocarbon fuels, which can severely limit the functionality of pellistor sensors. With fewer maintenance issues and longer lifespans, IR sensors offer a safer and more durable solution for many industries.

• Maintenance

IR sensors generally require less frequent maintenance than other sensors. They are immune to chemical poisoning and do not suffer from the same degradation issues. Regular calibration is still recommended to ensure accurate readings, especially in high-use environments. IR sensors also require significantly less power than other sensors, making them ideal for applications with limited power availability.

Limitations of IR Sensors

• Requires calibration for specific gases
• May saturate at very high gas concentrations
• More expensive than pellistor sensors