Technology
Measurement
Breath alcohol measurement is based on Henry's law: the concentration of a volatile substance in the air above a fluid is proportional to the concentration of the volatile substance in the fluid. In case of blood alcohol content the following relation holds:
1 gram of ethanol in 1 liter (or 1kg) of blood corresponds to 0.5mg of ethanol in 1 liter of exhaled air.
Blood alcohol content (BAC) is usually measured in grams per liter (g/l or pro mille) or in percentage (% BAC).
Numerous resources are available on the web with details about breath alcohol testing.
Alcohol testers must be calibrated periodically to maintain their accuracy. Calibration frequency requirements depend on usage, and therefore will vary from case to case. In determining your own requirements, you may wish to start by having your unit checked for calibration accuracy on at least a quarterly basis. An immediate calibration check is recommended if at any time you suspect the unit may not be giving an accurate reading.
Absent manufacturer's guarantee, ABECQ s.a.r.l. systematically tests and calibrates ALL products before shipping.
How to choose an alcohol tester
Semiconductor or Electrochemical (Fuel Cell) sensor?
There are two main types of alcohol sensors used in electronic breath alcohol testers - semiconductor and electrochemical. The first type is cheaper, but less precise and stable. Non-linearity of the output constrains the testers with a semi-conductor sensor to two-point calibration. Electrochemical sensors are more precise, stable, and more selective to alcohol (i.e. do not react to tobacco and other substances which can be present in a breath sample). These sensors are highly linear, so they can be tested and calibrated at a single concentration of the alcohol solution or dry gas. Most (if not all) individual testers are generally equipped with semi-conductor sensors.
There are some quality products based on the semi-conductor technology, designated for professional use. However, most professional testers use electrochemical sensors.
Mouthpiece or no mouthpiece?
Mouthpiece assures that a sufficient breath sample is taken for reasonably precise results. Other things equal, a device with a mouthpiece provides more precise and more stable results. This comes at a price - mouthpieces have to be periodically purchased.
Indications of models without mouthpiece vary depending on the distance of the sensor intake from mouth, direction and force of breath. Such models are intended for individual use only and the user can very quickly "feel" how the tester works. So, assuming there is no intention of self-deception, no-mouthpiece models provide very good measurement results from the point of view of precision and stability at a reasonable price.
If the alcohol tester is designated for professional use (police, transportation, industry), then only models with mouthpiece should be considered.
