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Professional Terms for Gas Analysis and Detector

Gas detectors are classified according to the detection principle. The flammable gas detection includes catalytic combustion type, semiconductor type, thermal conductivity type and infrared absorption type; toxic gas detection includes electrochemical type, semiconductor type, etc.; oxygen detection has electrochemical type, etc. Today The editor will share with you those professional terms of gas analysis and detection instruments.


“Parts PerMillion” (PPM) concentration measurement unit, generally used in the field of gas detection. For example: 1PPM of hydrogen sulfide in mixed air means that every million unit volume of gas contains one unit volume of hydrogen sulfide.

Explosion threshold

Flammable limits are divided into lower explosion level (Lower ExplosiveLevel) and upper explosion level (Upper ExplosiveLevel). The unit of LEL and UEL is usually a percentage, which refers to the percentage of a certain gas contained in the air (or oxidant). In an environment below LEL, there is too little combustible gas to burn. When the concentration of combustible gas in the environment is higher than UEL, it will not burn due to too much gas. The LEL and UEL values ​​of various combustible gases can be obtained in the relevant information.


Threshold Limit Values ​​(TLV) TLV means that when the content of a certain gas in the air is less than this threshold, the health of workers who are fully and continuously exposed to the environment will not be harmed. When referring to this value, the standards promulgated by the country must be the standard, and the new revised value should be adopted.

TVL includes the following two parts: the average threshold (TLV-TWA) This value represents the average concentration value weighted by time in the environment. When most workers work in this environment on an 8-hour daily and 40-hour weekly schedule, they will not have health problems. Instantaneous threshold (TLV-STEL) This parameter is defined as a 15-minute weighted average. The concentration of a certain hazardous gas in the workplace at any time on a working day shall not exceed its specified threshold, even if the total The weighted average of has reached the average threshold. The number of times exceeding the average threshold and lower than the instantaneous threshold shall not exceed 4 times in a day, and the duration of each time must be less than 15 minutes.

Dangerous concentration

Dangerous Concentration (IDLH) If the worker does not wear a gas mask or lacks escape experience, and the gas concentration in the working environment reaches a dangerous concentration, then a 30-minute stay will cause damage to the human body or weaken the health of the human body (such as reduced vision).

Explosion-proof mark

The country has clear regulations on various explosion-proof types of explosion-proof electrical equipment used in explosive environments. In dIICT6, d means that the explosion-proof type is explosion-proof, II means electrical equipment used in factories, and C means the maximum test safety gap or minimum ignition current ratio of explosive gas mixtures. (A, B, C three levels) the most stringent level, T6 represents the most stringent level that allows high surface temperature (85℃)

Explosion range

Explosion range (explosionrange) In the mixture of combustible gas and air, the concentration range between the lower and upper explosion limits of combustible gas is called the explosion range. Town gas generally includes natural gas, liquefied petroleum gas and artificial gas.

Response time

Under the test conditions, the time from when the detector touches the gas to be measured until it reaches a stable indication value. Generally, the time taken to reach 90% of the stable value is taken as the response time.

Recovery Time

Under the test conditions, the time from when the detector is separated from the gas under test to when the monitoring state is restored. Normally, the time for reading to recover to 10% of the stable indication value is regarded as the recovery time.

zero gas

Clean air or nitrogen that does not contain the measured gas or other interfering gases.

Standard gas

The composition, concentration and accuracy are all known gases.

Sensor preheating

After the sensor is powered on, the output value is unstable, and the period of waiting for the output value to stabilize becomes the sensor warm-up.

sensor poisoning

When the sensor is energized, if it comes into contact with a gas whose concentration is far beyond its range, it may cause the sensor’s output value to remain high. Some of the poisoned sensors can be recovered after a period of time, and some cannot be recovered.

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