Common unit:

(1) VOL%: refers to the volume ratio of the concentration of the mixed gas. 

(2) LEL%: refers to the percentage of the lower explosion limit of the combustible gas. 

(3) ppm: ppm is the abbreviation of part per million in English, which means one part per million. The volume concentration (ppm) indicates the volume of the target gas contained in one million volumes of air. 

(4) ppb: ppb is the abbreviation of part per billion in English. It is a unit symbol for the concentration of liquid or gas, which means one part per billion and is usually used in situations where the concentration is very small.

Common parameters of gas sensors:

Lower Explosive Limit(LEL) of Combustible Gas

Definition: The Lower Explosive Limit (LEL) of combustible gas refers to the lowest concentration of combustible gas that can explode when mixed with air (or oxygen) and encounters a fire source.

Query through the "Explosive Limit Table of Different Combustible Gases":

The lower explosion limit of methane is 5%VOL (50000ppm);

The lower explosion limit of propane is 2.1%VOL (21000ppm);

The lower explosion limit of hydrogen is 4%VOL (40000ppm).

Range:

Basic definition: The measuring range refers to the gas concentration range that the sensor can detect and measure normally. The measuring range is divided into upper and lower limits. The upper limit refers to the maximum concentration that the sensor can measure, and the lower limit refers to the minimum concentration that the sensor can measure. 

Professional definition: The highest gas concentration that can guarantee the parameters listed in the sensor specification. (That is, the sensor can only reflect its performance and parameters under the gas concentration within the measuring range)

Basic error:

Definition: The maximum deviation between the measured value and the true value of the sensor under reference environmental conditions (such as normal temperature 20±2℃, normal pressure 101.3kPa, standard gas concentration, and no interfering gas), usually expressed as a percentage or absolute value.

Resolution Ratio:

Definition: Resolution refers to the minimum change in the target gas concentration that the sensor can detect and distinguish, that is, the minimum interval of concentration values that the instrument can accurately reflect when measuring. In layman's terms, it is the "minimum scale" of gas concentration that the sensor can reliably identify.

Lower Detection Limit(LDL):

Definition: The lower detection limit (LDL) refers to the lowest concentration of the target gas that the sensor can reliably detect (usually with a signal-to-noise ratio of S/N ≥ 3). When the gas concentration is lower than this lower limit, the sensor may not be able to accurately identify or output a stable signal. This indicator is a core parameter for measuring sensor sensitivity and performance, and is particularly important in scenarios that require early warning (such as trace leak detection and occupational health monitoring).

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