How To Select A Calibration Gas

Calibrating a gas detector consists of adjusting the zero and the sensitivity.

To adjust the zero, I recommend using a bottle of reconstituted air (20.9% O2), with no traces of gas or other impurities. For oxygen (O2) or carbon dioxide (CO2) detectors, nitrogen must be used since air naturally contains 20.9% oxygen and 300 to 500 ppm of CO2.

Please read the recommendations below before adjusting sensitivity.

  1. Electrochemical, catalytic and semi-conductor cells require oxygen to operate. For example, a catalytic cell designed to detect explosive gas requires a minimum of 10% oxygen in the air. A semi-conductor cell requires at least 18% oxygen or it will underestimate the amount of gas. Therefore, it is important that the excipient of the bottles used be air and not nitrogen.

 

  1.  possible, the detector should be calibrated with the gas to be detected. Although for catalytic detectors there are equivalents (bottled gases of all substances do not exist), an infrared detector must not be calibrated with a gas other than the target gas. In this case, only a test with an interfering gas is possible (e.g., an infrared detector calibrated at the factory using gasoline will then be tested using propane).

 

  1. Propane, butane or pentane are often recommended for hydrocarbon detection (0-100% LIE range), although a hydrogen detector should be specifically calibrated with hydrogen and a methane detector with methane.

 

  1. We recommend using a standard gas concentration of between 20 and 80%, inclusive, of the detector’s range and/or closer to the alarm thresholds.

 

Example: A 0 to 1000 ppm CO detector. The recommended calibration gas is CO with a concentration in air of between 200 and 800 ppm, inclusive. Although the response is perfectly linear throughout the range (calibration at a single point is sufficient), I always recommend getting as close as possible to the alarm’s set thresholds. Also, if the alarm is set at 500 ppm, I recommend using this concentration as the test gas. Similarly, if the alarm is set at 100 ppm, I then recommend using a bottle of 100 ppm CO in the air, even if a 0 to 300 ppm detector seems to be better suited in that case.

 

Michel Spellemaeker

Global Director of Product Management