PORTABLE BREATH ALCOHOL ANALYZER BY NDIR METHOD Dr. Tetsuzo KITAGAWA, Tokihiko YONEDA, Shigefumi NAKAJIMA KOMYO RIKAGAKU KOGYO K. K. 2-14,2-chome, Nakane, Meguro-ku, Tokyo 152, Japan 1. Preface For the purpose of preventing from traffic accidents, it is practical to measure the alcohol concentration in breath of a driver, because breath sampling is done more easily and quickly than blood sampling. In Japan the authorized control of drunken drivers has effectively been conducted by means of the detector tube method to determine the breath alcohol of a driver on the roadside over the past 2 0 - odd years. Recently we have developed a portable analyzer of breath alcohol by means of NDIR method. They have also confirmed that it was a quite adequated instrument for instantaneous measurement of breath alcohol with high accuracy and easy operation. 2. General Description of the Analyzer Although the NDIR method is in widespread use as a method of gas analysis with high accuracy, the instrument itself should be very large in size and difficult in handling for obtaining a high sensitivity. 754
The dimensions of the Breath Alcohol Analyzer now developed by us could be successfully reduced by making its absorption cell length only as 10cm. In the result, the relationship between alcohol concentrations and their output signals which usually obeys to the law of Lambert-Beer showed approximately the linear correlation. Consequently, the digital display could be obtained by a decoded concentration signal without requiring a logarithmic amplifier nor linearizer. Futhermore, the instrument is provided with a solid state detector (PbSe) of high sensitivity and a low-noise preamplifier having a temperature compensation circuit by automatic gain control (AGC). The external view of the Breath Alcohol Analyzer is shown in Fig.l and its specification in Table 1. 1 Digital panel meter 2 Reset button 3 Measuring button 4 Printer 5 Mouthpiece Fig. 1 External View of Breath Alcohol Analyzer 755
Table 1. Specifications of the Portable Breath Alcohol Analyzer by NDIR Method Measuring principle : NDIR Method Measuring range : Alcohol 0.01 to 1.99 mg/4. in breath (or 0.02 to 4.00 o/oo in blood) Measuring accuracy : Less than +0.02 mg/ Indication : Digital meter and printer Breath sampling : Direct breathing into the mouthpiece and a sampling pipe (for five seconds) Measuring time : About 30 seconds from breathing into the analyzer to the data printing Working ambient temperature : 0 to 40 C Power supply : AC 100V. 50/60Hz (DC 12V. on option] Power consumption : 60 VA. Weight : 7.6 kg. Dimensions : 330 (W) x 380 (D) x 160 (H) mm 3. Composition and Operation of the Analyzer The Breath Alcohol Analyzer principally consists of the following three parts, that is, an air passage part for sampling the breath air, an analyzing part for measurement of the sample air, and an elec -trical circuit part, by means of which the analyzer's operating steps are confirmed, the measured value is digitally displayed and the final result can be printed out on a tape of paper. 3.1 Air Passage Part The flow diagram of the air passage part is shown in Fig.2. The area inside the broken line in Fig.2 is kept at the temperature of 35 C or the above, which is higher than the human breath temperature (34 C) in order to prevent condensation of moisture when 756
the breath is directly blown into the instrument. When the breath is blown into the analyzer from the mouthpiece attached on the tip of the sampling pipe, it passes through the pipe and filter and is led into the absorption cell in the analyzing part. The breath air subsequently passes through a flow sensor and is finally discharged from the instrument. Upon completion of a measurement, clean hot air is supplied from a heated cabinet through the pipe in the reverse direction by the pump operation in order to sweep out the remaining sample air and to prevent from cooling the pipe. Mouthpiece Fig.2 Flow Diagram 3.2 Analyzing Part The analyzing part, as shown in Fig.3, consists of an infrared light source, a chopper wheel, a detecting cell, a reference cell and an infrared detector. 757
The infrared ray emitted from the light source is divided into the detecting and the reference rays by means of a curved mirror and they are projected alternately into the cells through a band pass filter (BPF) installed on the opening of the chopper wheel, which selectively passes the infrared ray of around 3.4/twi in wavelength corresponding to the stretching vibration frequency of the C-H bond of an alcohol molecule. The infrared ray after passing the cells is gathered by a mirror into the detector and converted Into an electric output. Light source Chopper wheel Fig. 3 Construction Chart and Block Diagram 758
R D R D A Time R : Reference pulse D : Detecting pulse Fig. 4 Output from the Detector As shown in Fig.4, the outputs come out on the time axis as their representative pulses. If some amount of alcohol is detected, the pulse is reduced by absorbance of the infrared ray as shown by the pulse A in Fig.4. The alcohol concentration can be measured by comparing the pulse A to the reference pulse R. A photo-coupler is also installed in obtain a synchronous signal. the chopping system to 3.3 Electrical Circuit Part The electrical circuit part has a system for displaying and printing the concentration signal coming from the analyzing part with temperature compensation. It has also a system for controlling the operating signal. A simplified operation chart is shown in Fig.5. When the power switch is turned on, the air passage part is auto -matically heated. When its temperature gets on or over 35 C, the warming-up period is completed and the blue lamp is alight, notifying the completion of the measuring preparation. Then, the measuring button is pressed and the breath air is blown into the Analyzer through the mouthpiece. After five seconds of breath supply, the luminous diode is lighted, notifying the comple -tion of the sampling, and on the same time, the measured maximum 759
1 about 15 min. I about 30 sec. about 30 sec. Note : : measuring operation step : repeated manual operations : automatic check, compensation circuit operation point ) : external display Fig. 5 Operation Chart
alcohol content is displayed on the digital panel meter. The temperature is detected by the thermo-sensor and the read-out is automatically compensated. Subsequently, the concentration value on the digital panel meter is printed by the printer on a paper tape, but the figure on the panel meter is displayed until the reset button is pressed. When the reset button is pressed, the air passage part is purged by the warm air flow and the preparation for the next measurement is completed within about 30 seconds. The automatic zero adjustment circuit which operates simultaneously with the operation of the reset button contributes to the stable operation of the Analyzer. Calibration is needed only once or twice a year. 4. Performance Tests 4.1 Comparison with Gaschromatography The results of a comparison test of the NDIR Breath Alcohol Analyzer with the gaschromatography are in Table 2 and Fig.6. linear correlation was obtained between them. A good 4.2 Long-Term Stability The stability of the sensitivity of the Analyzer was tested by operating it for 24 hours at an ambient temperature of 20 C + 5 C. The results revealed that the sensitivity remained within the variation of less than + 0. 0 2 mg/x Moreover, the variation of the sensitivity after one month of continuous operation of eight hours a day did not exceed + 0. 0 2 mg//. 4.3 Temperature Characteristic The sensitivity variation caused by the temperature change in 761
the range of 0 C to 40 C was almost negligible as shown in Table 3. 4.4 Reproducibility The results of reproducibility test by measuring alcohol concentrations three times with an interval of one minute for each measurement showed an accuracy within + 0.01 mg/. as shown in Table 4. 4.5 Interfering Substaces Though the Analyzer may be interfered by the organic vapour having an alkyl radical, it became clear that the interfernce was quite a few in any concentration of organic vapour which could possibly exist in the human breath when he was exposed to the atmosphere containing the vapour as shown in Table 5. Effects of gases or vapours likely to be contained in foods or soft drinks were investigated and no effect could be found as shown in Table 6. Table 2 Comparison Value between Gaschromatography and NDIR Breath Alcohol Analyzer Measured Values of Alcohol n Saschromatography Breath Alcohol Gaschroma Breath Alcohol Analyzer tography Analyzer 0.0X9 0 02 0.366 0.36 0.042 0 04 0.378 0.37 0.054 0. 04 0.425 0.42 0.072 0. 07 0.450 0.43 0.107 0. 10 0.507 0.49 0.112 0. 11 0.562 0.56 0.138 0. 13 0.616 0.61 0.174 0. 17 0.825 0.83 0.203 0. 20 0.866 0.86 0.206 0. 20 0.906 0.92 0.233 0. 23 1.093 1.10 0.247 0. 24 1.102 1.11 0.273 0. 27 1.297 1.30 0.314 0. 32 1.464 1.48 0.344 0. 34 1.802 1.79 762
Fig. 6 Confirmation of Linearity Table 3 Temperature Characteristic Sample concentration (mg/jf) Indicated value (mg/jl) Temperature ( C) 0 1 0 2 0 30 40 0. 2 2 0. 2 2 0. 2 1 0. 2 2 0. 2 2 0. 2 2 1. 0 0 1. 0 1 1. 0 0 0.99 1. 0 1.1. 0 0 763
Table 4 Reproducibility Sample concentration (mg I#) Indicated Value (mg/j?) 1 st 2nd 3rd 0.31 0.31 0.31 0.31 0.60 0.59 0.59 0.60 0.89 0.90 0.89 0.89 1.19 1. 2 0 1. 2 0 1. 2 0 Table 5 Indicated Value for Organic Vapours Name of Gases Tested concentration ppm mg /J? Indicated value (mg /J?) Chloroform 35 0.076 0. 0 0 Dichloromethane 59 0.224 0. 0 0 Trichloroethylene 17 0. 1 0 0 0. 0 0 Acetone 25 0.064 0. 0 1 MEK 18 0.058 0. 0 2 Ethyl acetate 2 0 0.079 0. 0 2 Methanol 15 0. 0 2 1 0. 0 2 Toluene 30 0.123 0.03
Table 6 Effects of Other Substance Substance Indicated value (mg Ii ) Sampling conditions Water vapour 0.00 Saturated steam at 30 C Carbon monoxide 0.00 Concentration 5% Carbon dioxide 0.00 Concentration 5% Tobacco smoke 0.00 Breath immediately after smoking Garlic 0.00 Breath after eating 30 g of fried slices Ginger 0.00 Breath after eating 50 g of grated ginger Coca-Cola 0.00 Breath after drinknig 600 nup 5. Conclusions The main features of the NDIR Breath Alcohol Analyzer are characterized by high sensitivity and stability with simple operation and quick measurement. This is a suitable instrument for measuring breath alcohol on a roadside or in a police station and is expected to play an important role in controlling drunken drivers in the future. 765