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Breathalyzer Technologies And Sensors
Friday 26 July, 2013.
Electronic breath alcohol testers come in different designs with a wide range of prices. Some are relatively inexpensive and less sophisticated aimed at consumers, or others that are very expensive and sophisticated devices capable of producing test results that virtually mimic blood test. Electronic testers can also be classified as breath alcohol screening devices that covers most portable devices, or evidential desktop testers that are used for forensic testing admissible in the court of law.
With all the differences in looks and prices, today's most electronic breathalyzers can be classified according to their type of sensors they utilize. They are three types:
Semiconductor alcohol sensors are used in the least expensive breathalyzers with moderate accuracy. Fuel Cell testers sensors are more expensive and highly accurate used in more sophisticated and professional breathalyzers. Infrared sensors, are the most expensive and sophisticated type of testers that are most commonly used by certified personnel in law enforcement and in evidential / forensic applications.
Semiconductor sensors, also called Taguchi cells, measure a change in their characteristic impedance when exposed to breath alcohol. The sensor is heated up to a very high temperature (300 CÂ°). The tester measures the degree of oxidization of alcohol on the surface of the sensor. This surface impedance change translates to various scales of alcohol test results.
The Semiconductor sensors are not specific to alcohol vapors but they also respond to other gases closely associated with Ethyl alcohol such as methane and other organic gases like acetone in human breath breath. In practice, however, the only significant gas in a normal person breath is alcohol. A reading of .03 or higher can usually be attributed to alcohol. The reading of .01% to .02%, on the other hand, may be due to miscellaneous gas in a person's breath if the subject has not consumed alcohol in past 12 hours. Therefore, Testers using semiconductor sensors usually can not be relied upon to distinguish very low amount of alcohol from no alcohol at all. AlcAlret BT5500 Breathalyzer
Acetone is the one gas that may be found in larger quantities in the breath of some individual who are dieting or who are diabetic. In rare instances, very high levels of acetone may give significant reading on a semiconductor sensor, However, the issue of acetone has been greatly exaggerated by people trying to discredit breath alcohol test results. One researcher notes "It is long and tedious story which has little basis in fact. Most nonspecific claims are wholly spurious in that either the instruments do not respond at all to the alleged interference, such as Acetone, and/or that those compounds cannot appear in the breath of living and well subjects in sufficiently high concentrations to affect or be detected by a breath analyzer concerned. (" Recent Development in Alcohol Analysis, "Kurt M. Dubowski) Dubowski goes on to note that semiconductor sensors do, in fact, respond to acetone.
Because the semiconductor sensors are relatively inexpensive, a wide variety of testers have been made using these sensors. It is possible to manufacture a semiconductor based alcohol tester fairly inexpensively that will response to alcohol in some fashion. The more sophisticated and expensive breathalyzers do a much better job of controlling some of the factors that can distort results, such as temperature and humidity, and are able to produce near evidential quality test results.
Fuel Cell Breathalyzers
The Basic premise of the fuel cell was first developed in 1839 by sir William Grove, who noted that the electrical reaction occurred when one electrode was exposed to Hydrogen and another to oxygen, when both are immersed in sulfuric acid. Thus, the fuel cell generate electricity. While NASA has used the device to generate electricity in space, fuel cell has not been found to be practical method for electrical generation here on earth. instead fuel cell has become one of the most reliable alcohol sensors for portable breath alcohol testers.
Fuel cell is composed of a wafer with each surface coated with gold and platinum black, and sandwiched between a porous material containing a dilution of sulfuric acid. Electrode are attached are attached to each side of the wafer. When alcohol passes across the surface of the wafer, a chemical reaction takes place. Alcohol is converted into acetic acid and, freeing excess electrons. The small amount of electricity generated is directly proportional to the number of alcohol molecules that are present.
Fuel cell breathalyzers are expensive due to high cost of platinum as well as higher cost of a delicate and precise manufacturing process. Sometimes, the fuel cell sensor itself could cost higher the the entire semiconductor based breathalyzer. A Fuel Cell based unit has several advantages over the semiconductor based alcohol testers.
Fuel Cells respond to alcohol. Although they will respond to all type of alcohol, they do not react to acetone. Therefore, these units are ideal for distinguishing very low level of alcohol. Fuel cells breathalyzers can reliably detect levels as low as .01% BAC.
Fuel Cells are very selective when respond to alcohol. Although, they will respond to all type of alcohol, they do not react to acetone. Therefore, fuel cell breathalyzers are ideal for measuring very low level of alcohol. Fuel cell breathalyzers can reliably detect levels as low as .01% BAC.
Fuel Cells are probably the most accurate breathalyzer on the market. Given adequate Breath sampling and display capabilities, fuel cell based breathalyzers easily meet standards for evidential quality testing. Because fuel cell breathalyzers are sold in the mid to high price range, manufacturers can afford to incorporate a higher supporting technology to reduce errors and employ a more precise manufacturing process in order to produce superior products.
A second minor shortcoming of fuel cell is that repeated encounters with alcohol over short period of time cause the fuel cell to saturate and loose sensitivity to alcohol. unless the device is re-calibrated to make up for this loss of sensitivity, readings will be lower than actual by 10% to 15%. Although this is a concern for evidential testing, it is not a significant variation for most applications.
Evidential breathalyzer with Infrared absorption technology is entirely different from the semiconductor or the fuel cell based devices. In Infrared absorption technology, some measurable changes in energy and wavelength produced when alcohol vapor is injected into the infrared light chamber. These changes in energy and wavelength caused by the alcohol molecules are compared with the ambient values measured in the absence of alcohol. The actual alcohol level can then be calculated very precisely.
The main characteristic that differentiates infrared based breathalyzers from semiconductor and fuel cell testers is that no chemical reaction takes place with infrared devices. Both semiconductor and fuel cells oxidize the alcohol vapor in electro-chemical reaction. Both devices interact with the alcohol to measure it. Infrared sensors, on the other hand, do not interact with the alcohol in the sample; instead, it view the sample and measures the effect of alcohol on the infrared beam. Therefore, in infrared type breath testing, the original sample can be preserved for additional future analysis.
Infrared based testers have become the standard in past several years for evidential testing by law enforcement. The sophistication of Infrared based breathalyzers does not necessarily have anything to do with the actual sensing of the alcohol, but it ensures that legitimate and consistent breath samples are taken, the results are obtained only when the machine is working properly, and that the results are recorded in a tamper proof manner. All of these procedural factors add to the defensibility of the test results obtained with these machines. This is the whole point of evidential results as they often challenged in the court of law.
One capability of infrared technology is that some units can be calibrated by an internal absorption standard. For example, a quartz device can be made to precisely simulate the absorption effect of .100% alcohol level. Thus, the unit may be calibrated without the need for actual alcohol injected, which is necessary to calibrate most other type of alcohol testers.
Evidential Breath Testing DevicesGenerally expensive (costs range from $2000-$5000 per unit), require regular maintenance, repair and calibration, and must be operated by a trained and certified technician. Attachments such as sterile mouth pieces must be used each time a test is performed. These units are large table top designed to be used in one location. Relocation can through off their calibration settings which will require additional maintenance.
Portable Hand Held BreathalyzersThe portable breathalyzer is capable of providing fairly accurate results and are used for screening purposes. By measuring the alcohol content in the breath, a reliable indication of the blood alcohol level is achieved. Portables devices are less accurate than evidential devices, however by comparing the cost performance ratio, these devices are affordable and sufficient for personal usage. Most portable devices are not evidential and therefore they cannot be used in the court of law.
Disposable BreathalyzersThe disposable breathalyzer is a noninvasive, and non scalable method of screening for alcohol can be used to detect the presence of alcohol with a rough estimate to the degree of impairment. Being disposable, they are the most sanitary way to test. The disposable devices operate based on a known chemical reaction that is highly selective to to alcohol and less sensitive to other side gases. Unlike the semiconductor based sensors, the disposable devices are less likely to produce a false positive result. being disposable makes these type of devices are the most sanitary way to test public and at much lesser cost than portable units.