Correction Factors for EX LEL Catalytic Bead Sensors

Combustible gas detectors typically use catalytic bead sensors calibrated to methane. For specific applications, correction factors improve accuracy across different gases. These LEL sensors detect various combustible gases through a diffusion barrier that regulates gas flow to the catalytic element. This design creates heightened sensitivity to high-diffusion compounds, making them more responsive to small molecules like hydrogen and methane than to heavier hydrocarbons such as kerosene. Understanding these sensitivity variations is essential when deploying these sensors in diverse environments, where proper correction factors ensure reliable detection and measurement.

What are the Correction Factors for EX LEL catalytic bead sensors?

While calibrating with the specific gas of interest is ideal, Correction Factors (CFs) have been established to allow quantification of numerous chemicals using a single calibration gas, typically methane (which is the industry standard). This approach enables efficient and adaptable gas detection across a wide spectrum of combustible substances.

What is a Catalytic Bead Sensor for EX LEL?

Catalytic bead sensors are the predominant technology for detecting combustible gases in the %LEL range. These devices employ a dual-bead design: an active bead coated with a catalyst and an inactive reference bead. When flammable gases contact the active bead, oxidation occurs, generating heat that increases the bead's temperature. This temperature change alters the electrical resistance of the active bead. By measuring this resistance change and comparing it to the stable reference bead, the sensor produces a differential signal proportional to gas concentration. This simple yet effective mechanism enables precise detection of various combustible gases across industrial and safety applications.

How do I use Correction Factors?

There are a few ways you can use EX LEL correction factors for your catalytic bead sensor.

• Option 1 - Readout Adjustment. Operate your gas leak detector as normal. Let us assume it has been factor-calibrated to methane (the industry standard). So if the device reads 10% LEL registering from an ethanol source, we will use the correction factor for ethanol, which is 1.8 (see table below). Multiply 10% LEL to ethanol CF (1.8), which gives 18% LEL. This means the corrected (real) reading is 18% LEL.
  
  
• Option 2 - Calibration Adjustment. Calibrate the unit with methane (factory standard). Assume you are calibrating it to 25% LEL methane. You are certain you will exclusively use it for an ethanol detection (for example). In that case, your span calibration point will not be 25% LEL but will be 25% LEL x 1.8 = 45% LEL. The unit has been calibrated with and adjustment to read and display %LEL of ethanol. 
  
  
• Option 3 - Alarm Set Point Adjustment. Now assume you do not want to re-calibrate the unit to take into consideration the correction factor. You can do the inverse which is adjust the alarm set point to accommodate the correction factor. In this case, your alarm point will not be 25% LEL (methane) but instead will be 25% LEL x (1/1.8) = 14% LEL.

Correction Factors Table

The below table includes some common combustible gases and their correcting factors. These and others can be found here.

*LEL CF = Lower Explosive Limit Correction Factor