Measuring and testing – Gas analysis – Gas chromatography
Patent
1997-12-17
1999-07-27
Larkin, Daniel S.
Measuring and testing
Gas analysis
Gas chromatography
73 103, 73 106, 422 84, 436132, 436900, G01N 33497
Patent
active
059293195
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to breath testing apparatus for detecting volatile components, such as ethanol, in a subject's breath by oxidizing them in a fuel cell.
BACKGROUND OF THE INVENTION
Such apparatus is frequently used out in the open and may therefore have to operate in a wide range of temperatures. It is known that the fuel cell response is affected by temperature and attempts have been made to overcome this variation by heating the fuel cell so that it sits at or above a predetermined temperature by using thermistor control. However, this approach can cause problems both due to signal noise created by the heater and because it is difficult for the batteries in portable devices to supply sufficient current to run both the heater and the electronics associated with the fuel cell during the actual measurement process.
SUMMARY OF THE INVENTION
According to one aspect, the present invention consists in a breath testing apparatus including a fuel cell for producing an output signal, a housing for the fuel cell, a breath sampling means connected to the housing for drawing a breath sample into the fuel cell, a thermistor for detecting the temperature of the housing, compensation means for correcting the output signal of the fuel cell in accordance with the temperature detected by the thermistor, and means for displaying the corrected signal.
The apparatus may further include a heater, disposed within the housing, a thermistor for controlling the heater to maintain a part of the housing, adjacent the fuel cell, at or above a predetermined temperature, and means for disabling the heater during the operation of the fuel cell. The predetermined temperature is selected by the user based on conventional operating characteristics of the fuel cell and desired response set point of the heater. The thermistor for controlling the heater may also constitute the thermistor for detecting the temperature of the housing. The heater may be in the form of a coil or disc and the temperature-controlling thermistor may be disposed at or adjacent the center of the coil or disc.
The compensation means may include means for computing the corrected output of accordance with the following formula: ##EQU1## wherein BAC.sub.C is the corrected Breath Alcohol Concentration BAC.sub.A is the actual Breath Alcohol Concentration measured by the fuel cell; cell; housing; and
From another aspect, the invention consists of a method of operating a breath testing apparatus having a fuel cell in a fuel cell chamber, including detecting the temperature of the fuel cell chamber at the time the fuel cell is operational, calculating a correction factor in accordance with the temperature, applying the correction factor to the output of the fuel cell, and displaying the corrected output.
The correction factor may be: ##EQU2## wherein A is the concentration of the ethanol solution used to calibrate the fuel cell; its housing; and
The method may include the step of calibrating the fuel cell with a "wet" standard (e.g. one in which the calibration gas is an ethanol vapour generated by bubbling as though an ethanol standard) and the fuel cell may be heated. In this latter case, the heater may be switched off when or just before a sample is supplied to the fuel cell.
From a further aspect, the invention consists in a method of calibrating a breath testing apparatus having a fuel cell including supplying a "wet" standard and compensating the resultant output of the fuel cell in accordance with the temperature of the fuel cell or a housing containing it.
Although the invention has been defined above it is to be understood that it includes any inventive combination of the features set out above or in the following description.
The invention may be performed in various ways and a specific embodiment will now be described by way of example with reference to the accompanying drawing which is a schematic diagram of breath testing apparatus.
BRIEF DESCRIPTION OF THE DRAWING
The single drawing FIGURE illustrates the breath testing appa
REFERENCES:
patent: 3877291 (1975-04-01), Hoppesch et al.
patent: 3966579 (1976-06-01), Chang et al.
patent: 4749553 (1988-06-01), Lopez et al.
Maksimovich et al., "Device with Semiconductor Gas Sensor for Alcohol Vapour Detection in an Exhaled Air Sample", Sensors and Actuators B, vol. B13, No. 1/3, May 1993, pp. 256-258.
Aspinall Jason
King Paul
Larkin Daniel S.
Lion Laboratories Plc
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