Choosing the incorrect gas to calibrate your gas detectors will make the readings inaccurate and potentially unsafe. Here we explain which gas to use in order to ensure accurate and safe readings.
The selection of the correct combustible gas to calibrate your LEL gas detection device is first based upon your application.
In all cases you should select the calibration gas that best reflects the target gas that you are trying to measure. If you are a natural gas operation then methane would be the best choice. A LPG delivery company, then propane and if general measurement is required then pentane may be the best selection.
ALL catalytic combustible gas sensors will react to any combustible gas. How the sensor reacts is directly dependent upon which calibration gas was used to calibrate the sensor. Each sensor manufacturer will have a sensor response chart that details the relationship between calibrating a sensor to a specific gas and the response of the instrument.
Take an LEL sensor and calibrate it to Pentane.  If you expose the sensor to Methane gas the instrument will read higher than the true level of methane gas. If though, you calibrate the sensor to methane and then expose the sensor to pentane gas the instrument will read less than the true value of pentane gas. In both cases the reading are inaccurate, but the later means the instrument is potentially unsafe.
In general calibrating an instrument to a gas with a lower LEL value then the other gases measured will result in a more responsive instrument reading higher than the actual gas concentration.
An additional factor is the environment where the instrument is used. If poisons (silicone, airborne lead) or inhibitors (Sulphur or chlorinated compounds) are present in the atmosphere then LEL sensor sensitivity will be affected. In these situations, methane can be the best choice for calibration as it will provide the faster indication of sensor degradation.
So, in review:
- Calibrate to your target gas and you will have the most accurate readings.
- Use of pentane will provide a faster response to other combustible gases.
- When poisons or inhibitors are present the use of methane is recommended.
At all times the instrument of choice should be calibrated and bump tested to maximize the safety and accuracy of the instrument.
