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What is the principle of alcohol testing?
[ Huaqiang Security Network News ]
Before introducing the principle of alcohol detection, we will introduce what is an alcohol detector. The alcohol detector is an instrument used to detect whether the human body consumes alcohol or how much alcohol is ingested. It can be used as a detection tool for detecting the drinking of drinking drivers during traffic police enforcement to effectively reduce the occurrence of major traffic accidents. It can also be used to detect the alcohol content in human exhaled gases in other occasions to avoid heavy casualties and major losses of property, such as Some high-risk areas prohibit companies that are employed after drinking.
Principle of alcohol detection
When an oxide having N-type conductivity is exposed to the atmosphere, the amount of electrons inside thereof is reduced by the adsorption of oxygen to increase its electric resistance. Thereafter, if a certain reducing gas is present in the atmosphere, it will react with the adsorbed oxygen, thereby increasing the number of electrons in the oxide, resulting in a decrease in oxide resistance. The semiconductor-oxide sensor analyzes the gas concentration by the change in resistance.
Alcohol detection schematic
The alcohol tester is actually composed of an alcohol gas sensor (equivalent to a varistor that varies with the concentration of the alcohol gas) with a constant value resistor and a voltmeter or ammeter. As shown in the figure is its schematic. In the figure, R1 is a constant value resistance, and the resistance value of the alcohol gas sensor R2 decreases as the concentration of the alcohol gas increases. If the concentration of the alcohol gas exhaled by the driver is larger, the voltage indicating the tester is larger.
There are five basic types of equipment that can detect the alcohol content of a gas: fuel cell type (electrochemical), semiconductor type, infrared type, gas chromatographic type, and colorimetric type. However, due to the price and ease of use, only the fuel cell type (electrochemical type) and the semiconductor type are commonly used.
Fuel cells are environmentally-friendly energy sources that are widely studied all over the world. They can directly convert flammable gases into electrical energy without causing pollution. Alcohol sensors are only a branch of fuel cells. The fuel cell alcohol sensor uses precious metal platinum as the electrode, and the combustion chamber is filled with special catalyst, so that the alcohol entering the combustion chamber is fully burned and converted into electric energy, that is, the voltage is generated on the two electrodes, and the electric energy is consumed on the external load, and the voltage is entered. The concentration of alcohol in the combustion chamber is proportional.
Compared with the semiconductor type, the fuel cell type breath alcohol tester has the advantages of good stability, high precision, and good anti-interference. However, due to the extremely precise structural requirements of the fuel cell alcohol sensor, the manufacturing process is quite difficult. Only a few countries such as the United States, the United Kingdom, and Germany can produce it. In addition, the material cost is high, so the price is quite expensive, which is several times that of the semiconductor alcohol sensor. .
About the blowpipe
Although the blow pipe is small, it is very important to ensure the accuracy of the test. The mouth of the testee contains a blowpipe exhalation, and almost all of the gas entering the blowpipe is the gas exhaled by the test subject. If gas is fed from a bell mouth, the subject does not touch the bell mouth and blows the bell mouth. According to the principle of fluid mechanics, the pressure of the gas flows decreases, which brings the surrounding air into the instrument together (the sprayer is According to this principle, it is equivalent to diluting the alcohol concentration in the breath, and the detected alcohol concentration will be lower than the actual breath alcohol concentration of the testee. This problem should be noted.