What are the meanings of LEL%/VOL% and ppm in the gas detector
With the development of science and technology, gas detectors have been widely used in daily work in petrochemical, chemical manufacturing, pharmaceutical and microbiological industries, whether it is to detect gas concentration or gas composition, or to detect gas microleakage. An easy-to-use gas detector can provide a safe environment for our production and life. When we use the 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, etc., or on the LCD screen of the gas detector, also The words VOL% or ppm will appear, so 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 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 means that the volume of methane in the air is 5%. Many of the detection ranges of our gas detectors are 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 it in the air. The percentage 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)
We have introduced combustible gas before. The concept of combustible gas means that it can be uniformly mixed with air (or oxygen) within a certain concentration range to form a premixed gas. It will explode when encountering a fire source. Then, this combustible gas can The lowest volume percentage concentration for detonation, that is, the lower limit concentration of gas explosion is LEL%, which is referred to as the lower limit of explosion. His unit is also a percentage, that is, the lower explosion limit is divided into one hundred parts, one unit is 1LEL%, and the concentration of the gas volume in the lower explosion limit is expressed by VOL%.
3. PPM (one millionth of gas volume percentage)
The concept of PPM is similar to that of 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. Since the PPM unit is a dimensionless unit, large Some gas detectors that can detect PPM levels are used to detect gas micro-leakage in the working environment, because gas micro-leakage is very dangerous, and long-term gas micro-leakage may cause major accidents, so we need to use PPM-level gas detectors are used to eliminate micro-leakages in time.
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 of volume per million, so 1% (VOL)=10000PPM.
For the conversion of VOL and LEL, we need 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. For example, the LEL of hydrogen is 4% VOL, that is, when its volume percentage in air reaches 4% VOL, it will explode when it encounters an open flame. Therefore, 4% VOL is regarded as 100% danger, which is called 100% LEL , namely 4%VOL=100%LEL, then 1%VOL=25%LEL.
The conversion of PPM and LEL, there is no way to directly convert these two, 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, how much PPM is 20%LEL of methane, according to the calculation 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. We are familiar with what these three units represent and their conversions, which can help us better choose and use a gas detector.
