How to Calibrate Gas Detection Equipment
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 Daltonâ€™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
Atmospheric pressure recorded at the location where the gas detection measurement will be recorded
Since itâ€™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.
|Height above sea level||Static pressure|
|11 000||36,089||22 632.10||6.683245|
Table adapted from Wikipedia
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