What are the meanings of LEL%/VOL% and ppm in gas detectors
With the development of technology, gas detectors have become widely used in industries such as petrochemical, chemical manufacturing, pharmaceutical microbiology, etc. Whether it is detecting gas concentration, gas composition, or gas micro leaks, a user-friendly gas detector can provide a safe environment for our production and life. When we use gas detectors in daily life, the detection range on the liquid crystal label of the gas detector often appears with words such as 0-100LEL% or 0-2000ppm, or the words VOL% or ppm also appear on the liquid crystal display screen of the gas detector. So, what are the specific meanings of these three units and how they are converted? Today, we will give you a detailed introduction.
1、 VOL% (gas volume percentage)
VOL is a physical unit that describes the volume of a gas and is expressed as a percentage. It is the percentage of the volume of a specific gas in the air. For example, 5% VOL methane represents 5% of the volume of methane in the air. Our gas detector's detection range is often expressed in terms of VOL%. For example, the detection range is 0-100% VOL, which means that when detecting a certain gas, this gas detector can detect a proportion range of 0-100% in the air. We can also set a certain percentage value of VOL 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 explosive limit)
We have previously introduced the concept of combustible gas, which refers to the ability to uniformly mix with air (or oxygen) within a certain concentration range to form a premixed gas. When encountering an ignition source, it will explode. Therefore, the minimum volume percentage concentration that this combustible gas can detonate in the air, which is what we call the lower explosive concentration of gas, LEL%, or simply the lower explosive limit. His unit is also a percentage, which divides the lower explosive limit into 100 parts, with a unit of 1LEL%. The concentration of the gas volume inside the lower explosive limit is expressed in VOL%.
3、 PPM (parts per million by volume of gas)
The concept of PPM is similar to VOL, except that PPM represents one millionth of the volume of a gas. For example, 10ppm carbon dioxide refers to 10 parts per million of carbon dioxide in the air. Since PPM units are dimensionless, most gas detectors that can detect PPM levels are used to detect gas micro leaks in the working environment, as gas micro leaks are very dangerous, Long term gas micro leaks may cause major accidents, so we need to use PPM level gas detectors to promptly eliminate the areas of micro leaks.
4、 Conversion of VOL%, LEL%, and PPM
Firstly, the conversion of VOL and PPM is relatively simple, as% VOL is a percentage of volume and PPM is a part per million of volume, so 1% (VOL)=10000PPM.
To convert VOL and LEL, we need to first find out the lower explosive limit of the combustible gas. When the concentration of combustible gas in the air reaches its lower explosive limit, we call the explosion risk of the combustible gas environment in this place 100%. For example, the LEL of hydrogen is 4% VOL, which means that when the volume percentage in the air reaches 4% VOL, it will explode when exposed to an open flame. Therefore, considering 4% VOL as a 100% hazard, it is called 100% LEL, If 4% VOL=100% LEL, then 1% VOL=25% LEL.
The conversion of PPM and LEL cannot be directly converted. You need to first convert LEL to VOL, and then convert VOL to PPM. Here is a formula, PPM=% LEL × LEL (vol%) × 100, taking methane as an example, what is the PPM of 20% LEL methane? According to the calculation formula, it can be obtained as follows: 20 (% LEL) × 1 (% VOL) × 100=2000PPm. Generally speaking, the gas detectors that can detect PPM are very accurate, while LEL gas detectors are generally used in explosive testing situations, and the order of magnitude of VOL is the largest among them, which is also commonly used. We are familiar with what these three units represent and their conversions, which can help us better choose and use a gas detector.
