7Solutions Blog & News

LEL sensor

7Solutions in Gas Detection: Catalytic or Infrared LEL?

First let me introduce myself.

My name is Karel Wiersma and my adventure at 7Solutions started in 2017 when I started as an Account Manager.

Now I’m helping customers within the South-West of The Netherlands to advise them on their choice for gas detection.

With my background as a Safety Advisor, I’ve experienced being the end user of gas detection. During the past years I’ve been with 7Solutions, I’ve learned a lot more on the technical part of gas detection and the variety of choice. Due to this, it’s sometimes very difficult for the end user to choose the right detector with the right functions for their application. Helping customers choose the right detector for the jobs that they’re executing to make sure the detector keeps them safe from any potential exposure to toxic or flammable gasses and/or vapours, is what I like most about my work at 7Solutions.

One of the things I’ve noticed is that sometimes it’s not clear what LEL means and what the differences are between the two most common LEL sensors.


To create a fire or explosion, enough volume of flammable gasses or vapours must be present.

Therefore, every gas has a Lower Explosion Limit (LEL) and an Upper Explosion Limit (UEL). When the volume of the gas is between the LEL and UEL there is enough volume of gas to create a fire or explosion when enough oxygen and an ignition source are present. A LEL detector shows you how much percentage of the LEL is reached. E.g. The LEL of Methane (CH4) is 4,4 vol%. This is equal to 100% LEL. This means that when your detector shows 10% LEL there is 0,44 vol% Methane in the air or sample.

Catalytic or Infrared?

The two most common LEL sensors are Catalytic and Infrared.

The catalytic sensor uses the energy released during combustion to detect flammable gasses. In the sensor a combustion is created which releases energy when flammable gases pass. This energy causes the resistance to change. The difference in resistance is calculated to a percentage of LEL.

Infrared uses IR beams with different wavelengths. One that the flammable gas absorbs and one that isn’t absorbed. The difference between the two is calculated and shown as percentage LEL.


+ Can detect hydrocarbons, including hydrogen.

+ Is cheaper in purchase.

-Sensor can get poisoned due to high concentration of toxic gases e.g. H2S.

-Due to a combustion in the sensor, enough oxygen is needed to provide a correct reading.

-Life span of the sensor is shorter than IR. Where must be said that the life span of a sensor is depending on the maintenance of the sensor and exposure to gases.

-Has a high-power consumption causing shorter battery run time.


Infrared LED

+Sensor can’t be poisoned by high concentrations of toxic gasses.

+Sensor will keep working correctly in an environment with decreased oxygen concentration.

+Has a larger life span then a Catalytic sensor.

+Due to the Infrared LED technology the battery runtime using this sensor is very long (e.g. With the WatchGas QGM appr. two months without charging).

-Can’t detect hydrogen and acetylene.

-Infrared LEL sensors are more expensive in purchase.

Shortly said it is very important to know the application in order to choose the right type of LEL sensor to prevent usage of the wrong sensor.

If any help is ever needed for choosing the right detector for the right application, please feel free to contact our sales department. Within the product range of 7Solutions we can offer detectors with either Catalytic or Infrared LEL sensor (e.g. WatchGas QGM). We are willing to help you making the right choices to prevent accidents from happening!

Karel Wiersma – Product Manager


7Solutions has its own service and maintenance department where we can service any gas detection instrument, no matter what brand or age.

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