A “bump” or test procedure using a certificated standard gas mixture with a known concentration is the most effective way to determine this. Calibration is not required if the instrument is working well and continues to measure gas within tolerance. Any gas detector should undergo bump testing as part of routine maintenance. depending on the environment, general monitors gas detector calibration specific corporation standard operating procedures, manufacturer recommendations, sensing technologies, and recommended frequencies.
The NDIR and electrochemical sensor types are the two most used
NDIR sensors are calibrated before shipping and have a low tendency to wander. To make sure performance is constant, they need bump testing every six months or fewer. Only when bump testing shows the sensor is now out of specification is calibration required. Every three to six months, bump testing is needed for electrochemical sensors because they tend to drift over time. It is advised to calibrate once a year or if shock testing reveals out-of-spec sensors.
Electrochemical sensors use a particular technology that causes them to deteriorate over time and more quickly when exposed to a target gas. In addition, exposure to certain gases can make them poisonous. Bump testing should be performed more regularly if that was a danger. The importance of a gas detector can also influence calibration frequency. If the device is portable, it makes sense to bench calibrate it before using it in the field. Calibration should be done for this event if there will be a lot of traffic or work in the vicinity.