Before learning about how to calibrate breathalysers, it's useful to understand a bit about how they work. All portable breathalysers are designed to infer the blood alcohol content (BAC) of the user by analysing the amount of alcohol vapour in their breath. But how they do this varies: the type of sensor a breathalyser uses can greatly influence both the accuracy of measurement and the rate of drift.
Generally, portable breathalysers use either a semiconductor sensor or a fuel cell sensor.
Semiconductor sensors exploit the fact that the electrical resistance of certain semiconducting materials changes when exposed to alcohol vapour. Generally, tin oxide is used to make this type of sensor. Measuring the change in resistance of a heated tin oxide mesh gives a way of measuring the alcohol content of exhaled air.1,2 Semiconductor-type breathalysers are cheap and simple to make, making them common in personal breathalysers. However, measuring alcohol content in this way is not always very precise: these devices are much less accurate than those equipped with fuel cell sensors.
Fuel cell sensors, also known as electrochemical sensors, use specialised reagents that selectively react with alcohol molecules.3,4 The current produced by this electrochemical reaction is measured, and this measurement can be used to calculate the amount of alcohol present.5 Breathalysers fitted with this type of sensor are capable of making much more accurate measurements of alcohol in exhaled air than semiconductor sensors. These are generally more expensive than semiconductor-based breathalysers.
Unfortunately, there is no simple answer to this question! Drift rates vary between devices and users should always consult the manufacturer's specifications to ensure the best performance.
Of the two types of device, semiconductor-based breathalysers are more prone to drift. However, for both types of devices, manufacturers generally recommend calibrating every 6-12 months or every few hundred uses for personal devices.6,7 Breathalysers used for workplace or laboratory applications should be calibrated more frequently than this.
Of course, if your breathalyser is producing inconsistent or unusual results, it should be calibrated immediately.
The two primary methods of calibration for breathalysers are breath alcohol simulation and calibration gas mixture. Both these methods work by delivering a known concentration of alcohol of air to the breathalyser in air or nitrogen. If the reading on the breathalyser doesn't match the known concentration, the sensitivity of the breathalyser is adjusted accordingly.
A breath alcohol simulator uses a liquid solution of ethanol in water (an alcohol reference solution) to deliver a simulated breath to the breathalyser. A calibration gas mixture, on the other, hand uses a compressed gas canister containing a known concentration of ethanol in nitrogen.
Choosing reliable and precise calibration references is essential for accurate calibration of breathalysers. Air Products' calibration gas mixtures for breathalysers can be prepared with any ethanol concentration for the calibration of personal, workplace, or laboratory applications. Our mixtures are manufactured to the highest standards and are compatible with all major manufacturers of both handheld units and engine interlocks.
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