How to convert LEL%, VOL% and ppm in the gas detector
When using a gas detector in daily life, the detection range on the liquid crystal label of the gas detector often has words like 0-100LEL% or 0-2000ppm, or words like VOL% or ppm. What do these three units mean, and how are they converted?
1.VOL% (gas volume percentage)
VOL is a physical unit that describes the volume of a gas, expressed as a percentage, which is the percentage of the volume of a specific gas in the air. For example, 5% VOL methane means that the volume of methane in the air is 5%.
The detection range of gas detectors is often expressed in VOL%. For example, the detection range is 0-100% VOL, which means that when this gas detector detects a certain gas, it can detect its proportion in the air. The range is 0-100%.
We can also set the VOL of a certain percentage value as the alarm point. When the content of a certain gas reaches or exceeds this set value, the gas detector will alarm. This involves another unit, LEL%.
2.LEL% (lower explosion limit)
Combustible gas can be evenly mixed with air (or oxygen) within a certain concentration range to form a premixed gas, which will explode when encountering a fire source. The lowest volume percentage concentration of this combustible gas that can detonate in air, that is, the gas explosion lower limit concentration is LEL%, referred to as "lower explosion limit". The gas volume concentration of the lower explosion limit is expressed by LEL%, and its unit is a percentage, that is, the lower explosion limit is divided into one hundred parts, and one unit is 1LEL%.
3.PPM (one millionth of the gas volume percentage)
The concept of PPM is similar to VOL, except that PPM represents one millionth of the gas volume.
For example, 10ppm carbon dioxide means that the air contains 10 parts per million of carbon dioxide, because the PPM unit is a dimensionless unit.
4. Conversion of VOL%, LEL%, and PPM
The first is the conversion of VOL and PPM. The conversion of these two units is relatively simple, because %VOL is the percentage of volume, and PPM is the percentage per million of volume, so 1%VOL=10000PPM.
The second is the conversion of VOL and LEL. It is necessary to find out the lower limit of the explosion of the combustible gas. When the concentration of the combustible gas in the air reaches the lower limit of the explosion, we call the explosion hazard of the combustible gas environment in this place 100%. Therefore, considering 4% VOL as 100% risk, it is called 100% LEL, that is, 4% VOL=100% LEL, then, 1% VOL=25% LEL.
The third is the conversion of PPM and LEL. There is no way to convert these two directly. You must first convert LEL to VOL, and then convert VOL to PPM.
Here is a formula for everyone: PPM=%LEL×LEL(vol%)×100
Taking methane as an example, the PPM of methane at 20%LEL is calculated according to the formula: 20(%LEL)×1(%VOL)×100=2000PPm.
Generally speaking, the gas detectors that can detect PPM are very accurate gas detectors, and the gas detectors of LEL are generally used in explosion detection occasions. The order of magnitude of VOL is the largest among them, and it is also commonly used.
