Detection principle and operation method of alcohol detector
Alcohol detectors are instruments used to detect how much alcohol is ingested and 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.
Can be used to determine whether to drink and drive. There are two methods for detecting drunk driving: one is to detect the blood alcohol concentration of the human body, and the other is to detect the concentration of breath alcohol. In theory, the most accurate way to judge whether to drink or not is to check the alcohol content in the driver's blood. However, in the case of illegal behavior handling or routine inspection of road traffic, it is often unrealistic to extract blood on site. The simplest and most feasible method is to detect the alcohol content in the exhaled breath of the driver.
The breath alcohol tester is an instrument that detects the alcohol content of the driver's breath. When using the test, the test subject is required to have a mouth exhalation. If the subject is inhaled at a moderate rate and exhale for 3 seconds or more, the relationship between the alcohol content in the breath and the alcohol content in the blood is: blood alcohol Concentration = expiratory alcohol concentration × 2 200.
In the above formula, 2 200 is a coefficient. Due to the different conditions in different countries, the coefficient values ​​are different, the United States adopts 2,000, and Europe uses 2,100. Almost every country in the world uses a breath alcohol tester to perform on-site testing of the driver to determine if the person being measured is drunk driving. If the alcohol content of the driver's exhaled gas exceeds the specified limit, the instrument will display, the traffic police will print the test result in writing to notify the testee, and let the testee sign the approval on the spot as the legal evidence of the punishment for the driver. .
It is also possible to use enterprises that are prohibited from drinking in high-risk areas. The alcohol detector used by enterprises is not portable, but a wall-mounted alcohol detector. The wall-mounted type is convenient and convenient to use, and the detection speed is high and the precision is high. Benefits, wall-mounted type is more suitable for enterprises and institutions to use, increase credit card attendance, voice alarm, and other functions.
Detection principle
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.
Circuit diagram
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 fixed 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 of the tester is larger.
Types of
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 chromatography type, and colorimetric type. However, due to the price and ease of use, only fuel cell type (electrochemical type) and 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 an electrode, and is filled with a special catalyst in the combustion chamber, so that the alcohol entering the combustion chamber is fully burned and converted into electric energy, that is, a voltage is generated on the two electrodes, and the electric energy is consumed on the external load, and the voltage is entered. The alcohol concentration of the gas 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, it is very difficult to manufacture. 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 blowpipe 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.
Method of operation
1. Press the power switch, the instrument performs internal self-test and warm-up, and displays a countdown from 200 to 0, which lasts 20 seconds.
2. At the end of the timer, an audible prompt will be given, and the green light will be bright, and the yellow light in the middle will flash, indicating that the instrument is normal and can start detection.
3. The tube is blown into the air inlet for 4 seconds. If alcohol is detected, the buzzer will alarm and the red and green lights will flash at the same time. After 4 seconds, the concentration data is displayed. If the concentration is between 0.00 and 0.40, only the green light flashes; if it is greater than or equal to 0.50, only the red light flashes, accompanied by a rushing sound alarm. The instrument display turns OFF after the concentration data is held for 15 seconds. (Note: Since the sensitivity is extremely high in this display mode, if there is residue in the instrument
Alcohol gas will have a small number display. )
4. If no alcohol is detected from the air blow or no test is performed within 30 seconds after the power is turned on, the instrument display changes from 000 to OFF.
5. When the instrument displays OFF, you need to restart the measurement.
Recommendations
1. It is recommended to test after drinking for 20 minutes. This is because it takes about 20 minutes for the alcohol to be absorbed by the blood through the digestive system, and the remaining alcohol in the mouth also needs to be dissipated for such a long time.
2. Avoid testing in windy environments or in airy, closed rooms.
3. Do not blow the cigarette smoke into the instrument, as this will damage the sensor. Qiqi.com recommends waiting for 1 minute and then testing.
4. It is forbidden to blow smoke into the air hole. Do not enter the liquid in the air hole, do not block the air outlet.
5. The yellow light indicates that the power supply voltage is low and the battery needs to be replaced.
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