The catalytic bead lower explosive limit (CB LEL) sensor is widely used for combustible gas detection based on its low cost, ease of use, and the ability to detect a wide range of gases. However, for some special applications, such as environments with less than 10% vol oxygen (O2), the CB LEL sensor is not recommended. Here’s why:
Reason #1: 10% vol O2 allows gas readings up to 100% LEL.
To help you better understand this, let me explain the basic principle of how a catalytic bead LEL sensor works. A catalytic bead LEL sensor senses a combustible gas through flameless combustion that occurs with the help of electrically produced heat and a catalyst material coating on the sensing bead. In other words, a CB LEL sensor detects gas through the actual burning of the gas. This is why it can detect a wide range of gases and can detect multiple gases at the same time. Like three elements of a fire, CB LEL gas sensing requires fuel (combustible gas in this case), heat (by a metal wire coil buried in the sensor bead), and oxygen.