Common units of gas detection
1. Molar volume of gas: The volume of gas occupied by a unit of substance, with the symbol Vm, commonly measured in units of L/mol or m3/mol. Under standard conditions (0 ℃, 101KP state), the volume occupied by 1mol of any gas is approximately 22.4L.
2. Vol%: Refers to the concentration to volume ratio of a mixed gas.
3.% LEL: Refers to the percentage of the lower explosive limit of combustible gases. The LEL values of various combustible gases can be obtained from relevant data.
4. ppm (parts per million)/(1x10-6)/( μ)： Represents parts per million, or parts per million.
5. ppb: parts per billion, relative to ug/L, ng/g.
6. ppt: parts per trillion, relative to ng/L, pg/g.
7. Conversion of gas measurement units
(1) Conversion of Vol% to% LEL
Formula:% LEL=(V ÷ LV) × 100/Vol%=(L × LV) ÷ 100
V: The known volume ratio of combustible gas concentration, Vol%;
LV: The corresponding concentration to volume ratio of 100% LEL combustible gas, Vol%;
L: The percentage of known lower explosive limit of combustible gas,% LEL.
(2) .% Conversion of LEL to ppm
Formula: ppm=(L x LV) x 100/% LEL=PM ÷ (LV x 100)
PM: Known gas, ppm;
L: The percentage of known lower explosive limit of combustible gases,% LEL;
LV: The corresponding concentration to volume ratio of 100% LEL combustible gas, Vol%.
(3) Conversion of mg/m3 to ppm
Most gas detection instruments measure gas concentrations in terms of volume concentration (ppm). According to our country's regulations, especially the environmental protection department, gas concentration is required to be expressed in units of mass concentration (such as mg/m3), and our country's standards and specifications also use units of mass concentration (such as mg/m3) to represent it.
Using the unit of mass concentration (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 and pressure environmental conditions of the detected gas, and its value will vary with changes in environmental conditions such as temperature and pressure; During actual measurement, it is necessary to simultaneously measure the temperature and atmospheric pressure of the gas. When using ppm as a description of pollutant concentration, this problem will not occur as the volume ratio is used.
The conversion between concentration units ppm and mg/m3 is calculated using the following formula:
Mg/m3=M/22.4 * ppm * [273/(273+T)] * (Ba/101325)
In the above equation: M - is the molecular weight of the gas, ppm - the measured volume concentration value, T - temperature, Ba - pressure. This is the standard algorithm, but in our actual calculation work, temperature and pressure can be ignored. For the convenience of calculation and memory, it can be written as:
Please refer to the periodic table for the calculation of M molecular weight.
For example, what is the conversion of 100ppm H2S to mg/m3?
The M value of H2S is 1 * 2+16=18, which means 18/22.4 * 100=80 mg/m3. The opposite is also true.
