What do the units on the gas detector represent?
(1) % VOL (gas concentration to volume ratio): Detects oxygen and carbon dioxide, and uses this unit to directly read values.
(2) % LEL (lower explosive limit): refers to the minimum concentration at which an explosion occurs when a combustible gas is mixed with air and meets the minimum ignition energy.
Portable gas detectors usually have an alarm point set below 25% LEL of the lower explosive limit.
For example, the lower explosive limit of methane is 5% VOL, which means that 5% VOL is divided into 100 equal parts, corresponding to 100% LEL. When the detector value reaches the 25% LEL alarm point, it is equivalent to a methane concentration of 5% VOL * 25%=1.25% VOL at this time.
There is still a long way to go from the lower limit of 5% VOL for methane explosion, so there is no need to worry about the danger after the alarm. This is just a reminder to take corresponding measures immediately.
If the value reaches 100% LEL, it should be noted that the lower limit of methane explosion concentration of 5% has been reached, which is very dangerous.
(3) PPM: PPM is the abbreviation for part per million in English, representing parts per million, volume concentration (ppm), and the volume of pollutants contained in one million volumes of air.
Our national standards and specifications are also expressed in units of mass concentration (such as mg/m3).
What is the difference between a passive gas detector and an active gas detector?
Answer: Passive gas detectors mainly detect gas by flowing into the detector through gas flow; The active gas detector mainly sucks in ambient gas through a pump and enters the detector.
