What are "PPM" and "LEL" in gas detectors
We often see "PPM" and "LEL" marked on the gas detector, so what is "PPM" and "LEL", maybe many people are not very clear, the following four-in-one gas detector for everyone Let's introduce the specific meaning of these two words in detail.
"PPM" is the volume ratio concentration. "PPM" is a way of expressing the concentration of the solution, and PPM means one millionth. For the solution: that is, there is 1/1000 ml of solute in 1 liter of aqueous solution, and its concentration is 1 PPM. For gas: One of the ways to express the concentration of pollutants in the ambient atmosphere. Volume concentration expression: the volume of pollutants contained in one million volumes of air, that is, PPM, the gas concentration measured by most gas detection instruments is It is the volume concentration (PPM), and according to the regulations of our country, especially the environmental protection department, the gas concentration is required to be expressed in units of mass concentration, and the standard specifications of our country are also expressed in units of mass concentration. It uses some metal oxide semiconductors The material is manufactured based on the principle that the electrical conductivity changes with the composition of the ambient gas at a certain temperature.
"LEL" means lower explosive limit. The lowest concentration of combustible gas in the air when it encounters an open fire is called the lower explosion limit—abbreviated as %LEL.
Fixed VOC gas detector
The highest concentration of combustible gas in the air when it encounters an open fire is called the upper limit of explosion—abbreviated as %UEL. 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 only burn or explode when it is mixed with air to form a mixture or more precisely when it encounters oxygen to form a certain proportion of mixture. Relevant authoritative departments and experts have analyzed the combustion and explosion of combustible gases found so far, and have formulated the explosion limit of combustible gas, which is lower than the lower limit of explosion. The content of combustible gas in the mixture is insufficient to cause combustion or explosion. The oxygen content in the upper limit mixture is not enough to cause combustion or explosion.
In addition, the combustion and explosion of combustible gas are also related to factors such as gas pressure, temperature, and ignition energy. The explosion limit is generally expressed in volume percent concentration. The explosion limit is the general term for the lower explosion limit and the upper explosion limit. The concentration of combustible gas in the air will only explode when the concentration of the combustible gas is between the lower explosion limit and the upper explosion limit. No explosion will occur below the lower explosion limit or above the upper explosion limit.
Therefore, when carrying out explosion measurement, the alarm concentration is generally set below 25% LEL of the lower explosion limit. The measurement range of various combustible gas detectors is 0-100%LEL. Fixed combustible gas detectors usually have two alarm points: 10% LEL is the first level alarm, and 25% LEL is the second level alarm. Portable combustible gas detectors usually have an alarm point: 25%LEL is the alarm point.
For example, the lower explosion limit of methane is 5% volume ratio, that is to say, divide this 5% volume ratio into one hundred equal parts, so that 5% volume ratio corresponds to 100% LEL, that is, when the detector value reaches 10 When the %LEL alarm point is reached, it means that the content of methane is 0.5% by volume. When the detector value reaches the 25%LEL alarm point, it means that the methane content is 1.25% by volume.
Therefore, you don’t have to worry about whether there will be danger at any time after the alarm. At this time, it is reminding you to take corresponding measures immediately, such as turning on the exhaust fan or cutting off some valves. There is still a big gap, so that it will play the role of an alarm reminder. Of course, protective measures should be taken, and the instrument should be checked in time after the event to see if calibration is required.
