HK1208729B - Method for measuring breath alcohol concentration and apparatus therefor - Google Patents

Description

Method and device for measuring breath alcohol concentration

Technical Field

The present invention relates to a method for measuring the breath alcohol concentration of a user as defined in the preamble of claim 1. The method includes receiving a flow of a breath sample of a user and measuring a pressure of the flow of the breath sample. At the same time, the flow of breath sample is directed into the fuel cell sensor. The output signal of the fuel cell sensor is used to determine the volume of alcohol present in the breath sample, and thus the breath alcohol concentration.

In a second aspect, the invention also relates to a device for measuring the breath alcohol concentration of a user, as defined in the preamble of claim 10. The device includes a sampling component for receiving a breath sample of a user, a component for measuring the pressure of the flow of the breath sample, a fuel cell sensor, and a microcontroller. The microcontroller is adapted to calculate the volume of alcohol present in the breath sample, and thereby the breath alcohol concentration, based on the output signal of the fuel cell sensor. In a third aspect, the invention also relates to a breath alcohol interlock device comprising means for measuring the breath alcohol concentration of a user. In a fourth aspect, the present invention is directed to a vehicle comprising a breath alcohol interlock device.

Background

Generally, there are two technical solutions for measuring breath alcohol concentration, thereby determining the blood alcohol concentration of a person. In the first method, infrared spectroscopy is used, and a human breath sample is subjected to infrared radiation. Molecules in the breath sample absorb infrared light at a specific frequency, called the resonance frequency, which is characteristic of the molecule. For example, infrared absorption of ethanol molecules produces a specific infrared spectrum that is used to determine the amount of ethanol present in the breath sample, and thus the breath alcohol concentration. Although this method can achieve very high measurement accuracy, sensors incorporating infrared spectroscopy are expensive, thus limiting their use in mass-produced devices.

A second commonly used solution is based on fuel cell sensors that convert fuel in the form of alcohol (ethanol) into electric current by means of an electrochemical reaction. Fuel cell sensors have a slightly lower measurement accuracy than infrared spectroscopy sensors, but are much cheaper. However, fuel cell sensors require a breath sample with a detectable defined volume to properly determine breath alcohol concentration.

Conventional fuel cell-based analysis systems operate by a mechanical sampling system that introduces a preset specific volume of expiratory airflow into the fuel cell for analysis. The mechanical means may comprise an electric motor, a solenoid valve, a piston cylinder device, a diaphragm mechanism or a push button connected to a pump or bellows system. US patent US6,167,746 discloses a device comprising an electronically controlled valve to ensure that the necessary volume of expiratory airflow flows through the fuel cell. US2005/0241871 discloses a throttle interlock including a pressure transducer and a solenoid valve that operate independently of each other to provide a variable flow of exhaled air to a fuel cell. The microprocessor instructs the battery valve to remain open for a determined period of time to provide a preset breath sample volume and calculates an algorithmic correction factor based on the pressure reading to provide a pressure compensated alcohol result.

The methods described in the prior art involve advanced control circuitry and complex or bulky mechanical components, which all contribute additional cost to the system and limit the possibility of reducing the size of the system without reducing the measurement accuracy.

International application PCT/SE2010/051421, owned by the applicant of the present application, discloses a method and apparatus for measuring breath alcohol concentration and overcomes many of the problems of the prior art. However, the design of the mouthpiece of its device shows a non-linear relationship between its flow rate and the final reading. In other words, different flow rates produce different breath alcohol concentration measurements even though their breath samples have similar or identical alcohol concentrations.

There is therefore a need for an improved method that is capable of measuring breath alcohol concentration with high accuracy and that allows a compact measuring device to be manufactured at low cost.

Disclosure of Invention

It is an object of the present invention to provide an improved method which enables the breath alcohol concentration to be measured with high accuracy and which allows a compact measuring device to be manufactured at low cost.

According to the present invention, a method of determining breath alcohol concentration is provided. The method comprises the following specific technical means, as defined in the characterizing part of the independent claim 1. Based on the measured pressure, the volume of the breath sample is calculated by integrating the pressure of the breath sample over the expiration time. Throughout the time that the breath sample is being exhaled, the breath sample volume and the volume of alcohol present in the breath sample are continuously updated by integrating the measured instantaneous pressure and the fuel cell output signal over time. When the user stops blowing, volume compensation is performed: the stored calibration volume is used to perform compensation on the fuel cell output signal to obtain a volume compensated fuel cell output signal.

By volume compensating the fuel cell output signal, the measurement accuracy of the method and apparatus of the present invention is guaranteed, which is not affected by the volume of the breath sample. Since this method no longer requires the provision of a predetermined breath sample volume, the mechanical sampling systems used in the prior art become unnecessary, and the corresponding measuring device can be made more compact, with no or only few moving parts. So that the size and cost of the apparatus can be greatly reduced.

In a further embodiment, the method according to the invention comprises calculating a flow rate of the breath sample based on the breath sample volume and the recorded breath time, and performing a compensation of the volume compensated fuel cell output signal using a stored flow adjustment factor corresponding to the calculated flow rate to obtain a flow compensated fuel cell output signal. This allows the measurement to be adjusted to account for flow variations that affect the fuel cell output signal, thereby maintaining an accurate measurement of the breath alcohol concentration.

In a preferred embodiment, the method according to the invention comprises measuring a temperature and performing a compensation of the compensated fuel cell output signal using a stored temperature adjustment factor corresponding to the measured temperature. This allows the measurement results to be adjusted to account for temperature variations that affect the fuel cell output signal, thereby maintaining an accurate measurement of the breath alcohol concentration.

In a preferred embodiment, the method according to the invention comprises performing a calibration by measuring a sample having a predetermined volume and concentration if no measurement operation has been performed for a predetermined length of time, repeating the calibration step at least once and storing the resulting average value of the fuel cell output signal as a calibration volume. This allows the measurement to be adjusted to account for misleading first false high readings of the fuel cell, thereby maintaining an accurate measurement of breath alcohol concentration.

In a preferred embodiment, the method according to the invention further comprises determining the blood alcohol concentration based on the breath alcohol concentration and displaying the resulting blood alcohol concentration.

In a preferred embodiment, the method according to the invention comprises performing the compensation using the following formula:

in a further preferred embodiment, the method according to the invention comprises preventing the vehicle from starting if the calculated breath alcohol concentration exceeds a preset threshold.

In a further preferred embodiment, the method according to the invention comprises that the pressure is measured with a pressure sensor based on a pressure test, preferably with a venturi flow meter or orifice plate flow meter in combination with a pressure sensor. Pressure sensors based on pressure testing have the advantage of being able to provide a compact apparatus with no or only few moving parts, thereby being able to ensure an efficient use of the space within the apparatus device for performing the method of the invention.

According to the present invention, there is also provided an apparatus for determining breath alcohol concentration, as defined in independent claim 10. The device comprises the following specific technical features, as defined in the characterizing part of the independent claim 1. Based on the pressure measurement, the microcontroller is adapted to calculate the volume of the breath sample by integrating the pressure of the breath sample over the expiration time. The microcontroller is further adapted to continuously update the breath sample volume and breath alcohol concentration by integrating the measured instantaneous pressure and the fuel cell output signal over time. The microcontroller is arranged to perform a volume compensation of the fuel cell output signal to obtain a volume compensated fuel cell output signal, the compensation being performed when the user stops blowing.

Preferred embodiments of the device according to the invention comprise technical features corresponding to the preferred embodiments of the method described above.

In a preferred embodiment, there is provided a breath alcohol interlock device comprising an apparatus for determining breath alcohol concentration according to the present invention; a vehicle including the interlock device is also provided.

Brief description of the drawings

FIG. 1 is a graphical representation of fuel cell output signal over time;

FIG. 2 is a flow chart illustrating a method according to the present invention; and

fig. 3 is a schematic view of an apparatus according to the invention.

Detailed Description

The technical solution of the present invention will be further clarified by the detailed description of the embodiments with reference to the accompanying drawings. It is understood that the present invention should not be limited to the specific embodiments illustrated in the drawings and described below, but can be varied to include any combination of equivalent technical features, having a wide variety of embodiments, the scope of which is defined by the appended claims.

When an exhaled breath sample flows through the fuel cell of a breath alcohol concentration measuring device, also known as breathalyzer, any alcohol (ethanol) present in the breath sample is oxidized in an electrochemical reaction, producing a measurable current(this isA trademark owned). Fig. 1 shows the output response signal of a typical fuel cell in a graph of output voltage versus time. The area of the region under the curve can be calculated by integrating the voltage over time to obtain an FC value that is proportional to the alcohol concentration in the expired air.

To give an accurate measurement of breath alcohol concentration (BrAC), the breathalyzer must be calibrated using a standard sample of known alcohol concentration and volume. When subsequently performing a breath alcohol test on a subject, the breathalyzer requires a preset sample volume corresponding to the standard sample volume used for calibration. When the desired sample volume is provided, the breathalyzer compares the area under the fuel cell output signal (voltage) curve corresponding to the test sample with the stored standard values obtained by the calibration procedure to give a reading of the breath alcohol concentration being tested.

The requirement for a particular sample volume represents a major inconvenience in the use of breathalyzers known in the prior art. First, if the subject's lung capacity is small, or fails to provide a preset volume of breath sample for some other reason, for example, an effective breath alcohol concentration test cannot be performed. Second, the sampling mechanisms (e.g., pressure sensors, valves, pumps, etc.) required by breathalyzers to measure and obtain and supply a selected volume of breath sample to the fuel cell can be very expensive and/or bulky, thereby limiting the possibility of minimizing device size and reducing product cost.

The volume of the breath sample can be determined by calculating the area of the region under the curve of the volumetric flow rate of the breath sample as a function of time, which is proportional to the pressure of the flow of breath sample, in a similar manner to measuring the fuel cell output signal. Thus, the same result can be obtained by calculating the area of the region under the pressure curve, while the pressure can be measured in a more straightforward manner. Pressure can be more easily measured using a suitable pressure sensor, such as mechanical, pressure-based, optical, calorimetric or electromagnetic. In a preferred embodiment of the invention, a pressure sensor based on pressure testing is used, such as a venturi meter, orifice plate meter or equivalent in combination with a pressure sensor. Of course, a way of directly measuring the flow rate is also within the scope of the present invention.

Laboratory tests have shown that the expired volume V for any given breath alcohol concentration_bAnd fuel cell output signal FC_outThe change in (c) is linearly related:

FC_out＝k·V_b

stored calibration volume V obtained by using one measurement_calI.e. the value of the fuel cell output signal obtained when the device is calibrated with a sample having a predetermined volume and alcohol concentration, to output the signal FC to the fuel cell_outPerforming flow compensation and setting constant expression k as FC_our/V_bSubstituting into corresponding formula to obtain compensated value FC of fuel cell output signal_compThe following were used:

thus, the present invention achieves a new and innovative method of accurately measuring breath alcohol concentration of a subject, capable of handling a variety of different breath volumes, thereby eliminating the need for a sampling mechanism in the corresponding measurement device. In other words, the method and apparatus of the present invention are not limited by the volume of the breath sample, as they do not require the volume or flow of the sample to exceed a certain threshold in order to perform a breath alcohol concentration measurement.

Another problem arises when measuring breath alcohol concentration: the change in the fuel cell output signal is affected by the flow rate of the breath sample. The non-linear relationship between the flow and the fuel cell output signal arises, among other reasons, because of the design of the mouthpiece or air inlet duct of the device used to perform the measurement.

The flow rate of the breath sample, i.e. the total time the user takes to provide the entire breath sample, can be calculated by dividing the volume of the breath sample by the expiration time of the breath sample. Thus, in the method according to the invention, the expiration time is recorded for calculating the flow.

By obtaining test data at a wide range of different flow rates, using breath samples of predetermined volume and alcohol concentration while varying the breath time, the fuel cell output signal as a function of flow rate was found to fit exactly into the second order polynomial equation. Thus, the flow adjustment factor Q for performing flow compensation for the fuel cell output signal at any given flow Q can be reasonably deduced_f. Thus, an accurate measurement of the breath alcohol concentration can be maintained even if the flow rate affecting the output signal of the fuel cell is varied.

Thus, in a first step the calculation of the flow of the breath sample is performed as described above. Then, flow rate compensation is performed on the fuel cell output signal by multiplying the fuel cell output signal by a flow rate adjustment factor corresponding to the calculated flow rate and dividing by the calculated flow rate Q, thereby obtaining a flow rate compensated fuel cell output signal.

Problems affecting the accuracy of measuring breath alcohol concentration also exist: when the measurement device is idle for a period of time, during which it is not taking measurements, it will give misleading false high first measurements, even if recalibrated. To avoid such a falsely high first measurement result, it is recommended to perform the calibration at least twice. After at least two breath samples having a predetermined volume and alcohol concentration are measured, the average of the resulting fuel cell output signal is stored as a calibration volume for subsequent volume compensation. Subsequent measurements of breath alcohol concentration will maintain the required accuracy.

It should be appreciated that the output signal of the fuel cell varies with temperature. As the temperature decreases, the value of the fuel cell output signal also decreases. Such effects can be counteracted by temperature compensating the fuel cell output signal.

By obtaining test data at a wide range of different temperatures, using breath samples having a predetermined volume and alcohol concentration, the fuel cell output signal as a function of temperature was found to fit exactly into the second order polynomial equation. Therefore, the temperature adjustment factor T for performing temperature compensation for the fuel cell output signal at any given temperature can be reasonably deduced_f. Thus, the breath alcohol concentration can be kept accurately measured even if the temperature affecting the output signal of the fuel cell is varied. Preferably, the temperature range tested is between-10 and +50 ℃.

Thus, in a first step the temperature of the fuel cell and/or the environment is measured. Subsequently, the fuel cell output signal is adjusted by multiplying the fuel cell output signal by a temperature adjustment factor T corresponding to the measured temperature T_fAnd dividing by the measured temperature T, performing temperature compensation on the fuel cell output signal, thereby obtaining a temperature-compensated fuel cell output signal.

Another factor affecting the accuracy of the measurement of breath alcohol concentration is the fact that it is known that the fuel cell output signal slowly depletes or saturates as the alcohol concentration increases. In other words, the fuel cell produces a lower misleading output signal than would be expected for a given alcohol concentration.

By obtaining test data for a wide range of different alcohol concentrations, using breath samples having predetermined volumes and alcohol concentrations, the fuel cell output signal as a function of alcohol concentration was found to be a non-linear function at alcohol concentrations above about 0.5 mg/l. Thus, a linear adjustment factor for performing linear compensation for the fuel cell output signal at any given alcohol concentration can be reasonably deduced. Therefore, the breath alcohol concentration can be kept accurately measured even if the alcohol concentration affecting the output signal of the fuel cell is varied. Preferably, only alcohol concentrations above about 0.5mg/l trigger the linearity compensation.

Fig. 2 shows a flow chart of a method according to the invention. In a first step S201, the user starts blowing air into the measuring device, typically by means of a sampling tube or tube made of plastic or other suitable low-cost-to-produce, replaceable material, to ensure hygienic conditions for the user.

During the continuous blowing of the user into the measuring device, the pressure exerted by the flow of breath sample is measured and used to calculate the volume V of the breath sample_bValue of (b), the volume V_bCalculated by integrating the measured instantaneous pressure over time. In step S202, the resulting expiratory volume V is calculated by integrating the pressure over time_bThe value of (c) is continuously updated throughout the measurement.

At the same time, the breath alcohol concentration BrAC is output by the fuel cell signal FC_outCalculated and by outputting a fuel cell output signal FC_outIntegration over time, the breath alcohol concentration BrAC is also continuously updated in step S202.

In step S204, it is checked whether the user stops blowing. If the blow-in is indeed stopped, volume compensation is performed in step S205, as explained above, to obtain a volume compensated value FC of the fuel cell output signal_compThe value is used to countCalculating the compensated breath alcohol concentration value BrAC_comp. This breath alcohol concentration value may then be displayed to the user for review in step S206 and/or used to determine the blood alcohol concentration of the user.

Fig. 3 schematically illustrates a device for measuring breath alcohol concentration BrAC according to the invention. The measurement device is housed within a housing 1 and includes a replaceable breath sample inlet tube 2 for receiving a breath sample exhaled by a user or subject. The arrows in the figure indicate the direction of flow of the expiratory airflow through the measurement device. The expiratory airflow is led through a first channel 3, which first channel 3 is closed at the distal end. A pressure sensor 5 is provided near the distal end of the first channel 3 for measuring the instantaneous pressure of the breath sample flowing through the measuring device 1.

In a preferred embodiment, the pressure sensor 5 comprises a pressure sensor based on pressure testing, such as a venturi meter, orifice plate meter or equivalent in combination with a pressure sensor. However, the pressure may also be measured using any other suitable pressure sensor, such as a mechanical, pressure-based, optical, calorimetric or electromagnetic pressure sensor.

A portion of the expiratory airflow is directed through the sampling channel 4 into the fuel cell sensor 6 near the proximal end of the first channel 3. Any alcohol (ethanol) present in the breath sample will fuel the electrochemical reaction of the fuel cell 6, thereby generating an electrical current. The current becomes a measure of the alcohol content of the breath sample and is output via the fuel cell signal FC_outAs is evident, the output signal is typically represented as a voltage measured across the fuel cell 6.

Both the pressure sensor 5 and the fuel cell sensor 6 are connected to a microcontroller 7, which microcontroller 7 comprises means for data processing of the measured values of pressure and fuel cell voltage. In such a case, the data processing includes acquiring the pressure and the fuel cell output signal FC_outUnder the curve of timeArea of square region. The areas correspond to the volume V of the breath sample_bAnd breath alcohol concentration BrAC. The above result can also be obtained by outputting the pressure and the fuel cell output signal FC_outRespectively integrating the two with time. The microcontroller 7 is adapted to continuously update the breath sample volume V throughout the breath alcohol test_bAnd fuel cell output signal FC_out。

By varying the volume V of the breath sample, as described above_bThe flow Q is calculated by dividing by the recorded expiratory time of the expiratory sample. For this purpose, the microcontroller 7 comprises a timer or a timing member. In case the pressure measured by the pressure sensor 5 exceeds a predetermined threshold value, indicating that an expiratory sample is being supplied, the expiration time is recorded.

For measuring the temperature, the measuring device 1 comprises a temperature sensor (not shown). The temperature sensor measures the temperature of the fuel cell and/or the environment. The microcontroller 7 uses the measured temperature to perform temperature compensation based on the stored temperature adjustment factor corresponding to the measured temperature. The temperature adjustment factor corresponding to a temperature in the range between-10 c and +50 c may be stored in the microcontroller 7.

After the breath sample has passed through the fuel cell 6, it exits the housing 1 of the measuring device through the exhaust tube 8.

The measuring device further comprises a battery 9 or other suitable power supply to power the pressure sensor 5, the fuel cell 6 and/or the microcontroller 7.

In a preferred embodiment of the present invention, the measuring apparatus may further include a display section to display the measured breath alcohol concentration BrAC and/or blood alcohol concentration BAC. The blood alcohol concentration BAC may be calculated from the blood-air distribution coefficient, i.e. the relationship between the alcohol content in blood and the volume of breath given. Most breathalyzers use the international standard value of the partition coefficient of 2100:1, i.e., corresponding to 2100 parts of alcohol in blood for every 1 part of alcohol in breath.

The breath alcohol concentration measuring apparatus according to the present invention can be made very compact and be incorporated in a check interlock device. Such interlocking devices are well known in the art and will not be described in detail herein. The interlock device may include means for measuring the temperature, humidity and/or alcohol concentration of the user's expiratory airflow, and based on these measurements falling within an allowable range (corresponding to the user not being intoxicated), the interlock device permits activation of the vehicle or other mechanical device to which it is connected. Further, the interlock device may be provided with a microprocessor for analyzing the measurement result of the alcohol concentration measuring means, and a relay electrically connected to the starting device of the vehicle or machine.

When the alcohol concentration measuring device according to the present invention is provided, a compact and low-cost throttle interlock device for controlling the start of any vehicle or machine can be obtained.

Claims (23)

1. A method of measuring breath alcohol concentration BrAC of a user, comprising the steps of:

receiving a flow of breath sample from a user;

measuring the instantaneous pressure of the breath sample flow;

recording the expiration time of the breath sample;

-introducing the breath sample into a fuel cell sensor (6); and

based on the output signal FC of the fuel cell sensor (6)_outCalculating breath alcohol concentration BrAC;

calculating the volume V of the breath sample based on the measured pressure_b；

The method is characterized in that:

by measuring the resulting instantaneous pressure and the fuel cell output signal FC_outIntegrating over time, continuously updating the breath sample volume V_bAnd the breath alcohol concentration BrAC, the breath sample volume V not being taken into account during integration_bThe influence of (a);

based on the breath sample volume V_bAnd the recorded expiration time calculating the flow Q of the breath sample; and

after the user has stopped blowing, the following steps are performed before calculating the final value of the breath alcohol concentration BrAC:

using stored calibration volume V_calOutput signal FC to the fuel cell_outPerforming compensation to obtain volume compensated fuel cell output signal

Using a stored flow adjustment factor Q corresponding to the calculated flow Q_fAnd performing compensation on the volume compensated fuel cell output signal to obtain a flow compensated fuel cell output signal.

2. The method of claim 1, further comprising the steps of:

measuring the temperature T; and

using a stored temperature adjustment factor T corresponding to the measured temperature_fPerforming compensation on the compensated fuel cell output signal.

3. The method of claim 1, further comprising the step of, if no measurement operation has been performed for a predetermined length of time:

performing a calibration by measuring a sample having a predetermined volume and concentration;

repeating the calibration step at least once; and

subjecting the obtainedFuel cell output signal FC_outIs stored as a calibration volume V_cal。

4. The method of claim 1, further comprising the step of

Determining a blood alcohol concentration BAC based on the breath alcohol concentration BrAC.

5. The method of claim 4, further comprising the step of

The resulting blood alcohol concentration BAC is shown.

6. The method of any of the preceding claims, wherein the volume compensation is performed using the following formula:

compensated fuel cell output signal

7. The method of claim 1, further comprising the step of

If the calculated breath alcohol concentration BrAC exceeds a predetermined threshold, vehicle start-up is prevented.

8. The method according to claim 1, wherein the pressure is measured with a pressure sensor (5) based on a pressure test.

9. The method of claim 1, wherein the pressure is measured using a venturi or orifice meter in combination with a pressure sensor.

10. An apparatus for measuring breath alcohol concentration (BrAC), comprising:

-means (2) for receiving a breath sample of a user;

-means (5) for measuring the instantaneous pressure of the flow of breath sample;

means for recording the breath sample expiration time;

a fuel cell sensor (6); and

a microcontroller (7) adapted to:

output signal FC based on the fuel cell sensor_outCalculating breath alcohol concentration BrAC;

calculating the volume V of the breath sample based on the measured pressure_b；

Characterized in that said microcontroller (7) is further adapted to:

by measuring the resulting instantaneous pressure and the fuel cell output signal FC_outIntegrating over time, continuously updating the breath sample volume V_bAnd the breath alcohol concentration BrAC, the breath sample volume V not being taken into account during integration_bThe influence of (a); and

based on the breath sample volume V_bAnd the recorded expiration time calculating the flow Q of the breath sample;

using stored calibration volume V_calOutput signal FC to the fuel cell_outPerforming compensation to obtain a volume compensated fuel cell output signal;

using a stored flow adjustment factor Q corresponding to the calculated flow Q_fAnd performing flow compensation on the volume compensated fuel cell output signal to obtain a flow compensated fuel cell output signal.

11. The device according to claim 10, further comprising means for measuring a temperature T, wherein the microcontroller (7) is further adapted to:

using a stored temperature adjustment factor T corresponding to the measured temperature T_fPerforming compensation on the compensated fuel cell output signal.

12. The apparatus according to claim 10, wherein the microcontroller (7) is further adapted to: determining a blood alcohol concentration BAC based on the breath alcohol concentration BrAC.

13. The device according to claim 10, wherein the calibration is performed by measuring the sample with the predetermined volume and concentration at least twice if no measurement operation has been performed for a predetermined length of time, wherein the microcontroller (7) is further adapted to: the obtained fuel cell output signal FC_outIs stored as a calibration volume V_cal。

14. The apparatus according to claim 11, wherein the microcontroller (7) is further adapted to: determining a blood alcohol concentration BAC based on the breath alcohol concentration BrAC.

15. The device according to claim 11, wherein the calibration is performed by measuring the sample with the predetermined volume and concentration at least twice if no measurement operation has been performed for a predetermined length of time, wherein the microcontroller (7) is further adapted to:

the obtained fuel cell output signal FC_outIs stored as a calibration volume V_cal。

16. The apparatus according to claim 13, wherein the microcontroller (7) is further adapted to: determining a blood alcohol concentration BAC based on the breath alcohol concentration BrAC.

17. The apparatus of claim 15, wherein the microcontroller (7) is further adapted to: determining a blood alcohol concentration BAC based on the breath alcohol concentration BrAC.

18. The apparatus according to claim 17, wherein the apparatus further comprises a display means for displaying the resulting blood alcohol concentration BAC.

19. The apparatus of any one of claims 10-18, wherein the volume compensation is performed using the following equation:

compensated fuel cell output signal

20. The device according to any of claims 10-18, wherein the means for measuring the pressure comprises a pressure sensor (5) based on a pressure test.

21. The device according to any of claims 10-18, wherein the means for measuring the pressure comprises a venturi flow meter or an orifice plate flow meter in combination with a pressure sensor.

22. A breath alcohol interlock device comprising the apparatus of any one of claims 10-18.

23. A vehicle comprising the breath alcohol interlock device according to claim 22.