What does "PPM" in gas detectors stand for?
What does "PPM" mean in a gas detector? PPM "is the volume ratio concentration:" PPM "is a method of expressing the concentration of a solution, with PPM representing parts per million.
For a solution: if there is 1/1000 milliliter of solute in 1 liter of aqueous solution, the concentration is 1 PPM.
For gases: one of the methods for representing the concentration of pollutants in the ambient atmosphere.
Volume concentration representation method: The volume of pollutants contained in one million volumes of air, also known as PPM, is measured by most gas detectors as volume concentration (PPM). However, according to China's regulations, especially the environmental protection department, gas concentration is required to be expressed in units of mass concentration, and our country's standards and specifications also use units of mass concentration. It is manufactured using the principle that the conductivity of some metal oxide semiconductor materials changes with the composition of the ambient gas at a certain temperature.
If the concentration of a certain gas is 200 ppm, it means that there are still 200 cubic meters of this gas in 1 million volumes of air. Ppm is a commonly used unit for gas detectors and gas alarms, generally used for labeling non flammable and explosive gases or alarm indications (flammable and explosive gases are labeled with% LEL).
The use of mass concentration units (mg/m3) as a representation of air pollutant concentration can facilitate the calculation of the true amount of pollutants. But the quality concentration is related to the temperature, pressure and environmental conditions of the detected gas, and its value will vary with changes in temperature, pressure and other environmental conditions; During actual measurement, it is necessary to simultaneously measure the temperature and atmospheric pressure of the gas. When using ppm to describe pollutant concentration, this problem does not occur due to the use of volume ratio.
Most gas detection instruments measure gas concentrations in terms of volume concentration (ppm). According to Chinese regulations, especially the environmental protection department, gas concentration is required to be expressed in units of mass concentration (such as mg/m3), and our national standards and specifications also use units of mass concentration (such as mg/m3). What is the relationship between the concentration units of these two gases in mg/m3 and ppm? How to convert between them?
Conversion of concentration units from ppm to mg/m3
mg/m3=M/22.4·ppm·[273/(273+T)]*(Pa/101325)
In the above formula, M - represents the molecular weight of the gas; PPM - measured volume concentration value; T - Temperature; Pa - Pressure.
With this formula, we can easily obtain mg/m3 from ppm or calculate it in reverse.
