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How to Calibrate Gas Detection Equipment

How to Calibrate Gas Detection Equipment

Gas detection equipment may need to be calibrated according to the location.

Gas detection equipment can help detect and locate gas leaks and are an essential safety tool on sites where gas could potentially escape and pose a safety hazard to workers or the surrounding communities. However, from time to time, you may need to calibrate gas detection equipment at an atmospheric pressure (barometric pressure) that differs from the reading recorded at the measurement site. In cases such as this, you will need to apply a correction factor to correct for the atmospheric pressure differences between the two locations.

While gas concentrations are typically measured and reported as parts per million (ppm), according to Dalton’s Law of Partial Pressures, we are in fact only measuring and recording the partial pressure of the gas. Since, a change in ambient pressure is going to influence the pressure reading recorded by gas detection equipment, in cases where the gas detection equipment is going to be used at a site where the atmospheric pressure differs from the site where the equipment was calibrated, we need to correct the reading to account for these pressure differences.

How to Correct for Atmospheric Pressure Differences when using Gas Detection Equipment

In order to correct for differences in atmospheric pressure, the gas level reading reflected on the gas detection equipment must be multiplied by the correction factor below:

Atmospheric pressure recorded at the location where the gas detection equipment was calibrated

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Atmospheric pressure recorded at the location where the gas detection measurement will be recorded

Since it’s the ratio rather than the units that are important, regardless of what unit (kilopascals, millibars, inches of mercury, or millimeters of mercury) you are using to measure atmospheric pressure, you just need to be consistent.

To achieve the greatest accuracy, you need to take into account that barometers typically also need to be corrected for gravity and temperature.

On a final note, when gas detection equipment is being used onboard an aircraft, the cabin pressure reading rather than the external pressure needs to be considered.

The graph and table below illustrate how atmospheric pressure is affected by altitude/location.

Graph showing why gas detection equipment may need to be calibrated.

Credit: Geek.not.nerd Own work, via Wikipedia


 
Height above sea level Static pressure
(m) (ft) (Pa) (inHg)
0 0 101 325.00 29.92126
11 000 36,089 22 632.10 6.683245
20 000 65,617 5474.89 1.616734
32 000 104,987 868.02 0.2563258
47 000 154,199 110.91 0.0327506
51 000 167,323 66.94 0.01976704
71 000 232,940 3.96 0.00116833

Table adapted from Wikipedia
Featured Image by  fernandozhiminaicela via Pixabay
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