We often see "PPM" and "LEL" on the gas detector, so what are "PPM" and "LEL"? Perhaps many people are not very clear. The following four-in-one gas detector will introduce the specific meanings of these two words in detail.
PPM "is the specific concentration by volume. "PPM" is a representation of solution concentration, and PPM means one in a million. For solution: that is, there is 1/1000 ml solute in 1 liter of water solution, and its concentration is 1 PPM. For gas: one of the methods to express the concentration of pollutants in the ambient atmosphere. Volume concentration representation: The volume number of pollutants contained in one million volumes of air is PPM, and the gas concentration measured by most gas detection instruments is PPM. However, according to China's regulations, especially the environmental protection department, the gas concentration is required to be expressed in units of mass concentration, and our national standards and specifications are also expressed in units of mass concentration. It is made by using the principle that the conductivity of some metal oxide semiconductor materials changes with the change of environmental gas composition at a certain temperature.
"LEL" refers to the lower explosion limit. The lowest concentration of combustible gas that explodes when exposed to fire in air is called the lower explosion limit- percent LEL for short.
The highest concentration of combustible gas that explodes when it meets the fire in the air is called the upper limit of explosion- percent UEL for short. So what is the lower explosion limit? If the concentration of combustible gas is too low or too high, it is not dangerous. It will burn or explode only when it is mixed with air to form a mixture or, more precisely, when it meets oxygen to form a certain proportion of mixture. Relevant authorities and experts have made an analysis of the combustion and explosion of combustible gas found at present, and worked out the explosion limit of combustible gas. Below the lower explosion limit, the combustible gas content in the mixed gas is insufficient to cause combustion or explosion, and the oxygen content in the mixed gas above the upper limit is insufficient to cause combustion or explosion.
Therefore, in the explosion measurement, the alarm concentration is generally set below 25 percent LEL of the lower explosion limit. The measuring range of various combustible gas detectors is 0-100 percent LEL. The fixed combustible gas detector usually has two alarm points: 10 percent LEL is the first alarm and 25 percent LEL is the second alarm. Portable combustible gas detector usually has an alarm point: 25 percent LEL is the alarm point.
For example, the lower explosion limit of methane is 5 percent by volume, that is to say, divide this 5 percent by volume into 100 equal parts, so that the 5 percent by volume corresponds to 100 percent LEL, that is, when the detector value reaches the alarm point of 10 percent LEL, it is equivalent to the methane content of 0.5 percent by volume at this time. When the detector value reaches the alarm point of 25 percent LEL, it is equivalent to the methane content of 1.25 percent by volume.
