| 摘要 |
A tamper evident volatile substance breath analyser has inlet port 6 and adjacent microphone 9, positioned to measure pressure variations arising from an exhaled sample air flow. At least a portion of the sound signal is analysed to determine whether an untampered breath specimen is being provided, which may be indicated by dominance of frequencies below 400Hz. The breathalyzer may also include a carbon dioxide sensor 12, the acoustic waveform being stored in a buffer 16 before a portion, corresponding to a relevant predetermined time period, is analyzed when C02 concentration reaches a threshold value. A second microphone 10 may monitor ambient noise, allowing for subtraction from the main signal. The device prevents false negatives being given, for example should a user attempt to defraud the test by delaying alcohol-polluted breath from entering the device by using a tube. |
