How are LEL%, VOL%, and ppm converted in gas detectors
When using 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 with words such as VOL% or ppm. What are the specific meanings of these three units and how are they converted?
01
VOL% (gas volume percentage)
VOL is a physical unit that describes the volume of a gas, expressed as a percentage, which represents the percentage of a specific gas's volume in air. 5% VOL methane represents 5% of the volume of methane in the air.
The detection range of gas detectors is often expressed as VOL%, for example, the detection range is 0-100% VOL, which means that this gas detector can detect a certain gas in the air with a proportion range of 0-100%.
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 sound an alarm. This involves another unit, LEL%.
02
LEL% (lower explosive limit)
Combustible gas is a pre mixed gas that can be uniformly mixed with air (or oxygen) within a certain concentration range. When it encounters a fire source, it will explode. The minimum volume percentage concentration at which this combustible gas can detonate in air is LEL%, also known as the lower explosive limit. The concentration of gas volume at the lower explosive limit is expressed in LEL%, which is expressed in percentage. That is, the lower explosive limit is divided into 100 parts, with each unit being 1 LEL%.
03
PPM (parts per million of gas volume percentage)
The concept of PPM is similar to VOL, except that PPM represents one millionth of a gas volume.
For example, 10ppm of carbon dioxide refers to the air containing 10 parts per million of carbon dioxide, as the PPM unit is a dimensionless unit.
"Non dimensional unit" is a specialized term in astronomy, which includes pi, natural constant (e), radians (rad), and golden ratio( φ) And relative molecular weight (Mr), etc. On the contrary, there are dimensional quantities that have units such as length, area, time, etc.
Non dimensional quantities are often written as the product or ratio of two dimensional quantities, but their final dimensions eliminate each other, resulting in non dimensional quantities
Gas detectors capable of detecting PPM levels are all used to detect gas micro leaks in the working environment, as gas micro leaks are very dangerous and long-term gas micro leaks may cause major accidents. Therefore, it is necessary to use PPM level gas detectors to detect and eliminate micro leaks in a timely manner.
04
Conversion of VOL%, LEL%, and PPM
Firstly, there is the conversion between VOL and PPM. The conversion between these two units is relatively simple, as% VOL is the percentage of volume, while PPM is the parts per million of volume. Therefore, 1% VOL=10000PPM.
Secondly, the conversion between VOL and LEL requires first identifying the lower explosive limit of the combustible gas. When the concentration of the combustible gas in the air reaches its lower explosive limit, we call the explosion hazard of the combustible gas environment in this location 100%. For example, the LEL of hydrogen is 4% VOL, which means that when its volume percentage in the air reaches 4% VOL, it will explode when exposed to an open flame. Therefore, considering 4% VOL as 100% danger, it is called 100% LEL, which means 4% VOL=100% LEL. Therefore, 1% VOL=25% LEL.
The third is the conversion between PPM and LEL, which cannot be directly converted. LEL needs to be converted to VOL first, and then to PPM.
Here is a formula: PPM=% LEL x LEL (vol%) x 100
Taking methane as an example, what is the PPM of 20% LEL methane? According to the calculation formula, 20 (% LEL) x 1 (% VOL) x 100=2000PPm.
Generally speaking, gas detectors that can detect PPM are very accurate, while LEL gas detectors are generally used in explosion detection situations, and the order of magnitude of VOL is the largest among them, which is also quite commonly used.
