WO1998016812A9

WO1998016812A9 - Breath monitoring apparatus

Info

Publication number: WO1998016812A9
Application number: PCT/US1997/018355
Authority: WO
Filing date: 1997-10-10
Publication date: 1998-08-20

Abstract

An apparatus for measuring the concentration of a human breath constituent, such as alcohol, comprises a hand-held housing (12) having an internal breath passageway with a first end (14) through a nozzle (16) mounted to the housing. A waveguide-type integrating circuit sensor (18) for detecting the constituent is mounted in said chamber and provides an output signal corresponding to the presence of the constituent to be sensed. A pressure transducer (22) is coupled to the passageway for measuring the pressure therein to allow the validity of the breath sample to be determined.

Description

BREATH MONITORING APPARATUS

Background of the Invention

There have been numerous attempts to provide devices to determine the alcohol level of blood, which provides a legal definition for the offenses of driving while intoxicated or driving in an alcohol-impaired state. A common approach employed in such devices is the use of alcohol-responsive sensor adapted to measure the amount of alcohol in a breath sample to which the sensor is exposed. A sensor reading corresponding to a given breath alcohol concentration level can be correlated to an associated blood alcohol level, which information can be utilized to lock out an ignition circuit, issue an alarm, or provide other appropriate signal outputs when the sensed alcohol level exceeds a chosen reference value. The criteria of primary importance for an acceptable sensor system is that the sensor provide an accurate indication of the alcohol level of the breath and that it exhibits a high immunity to false or spurious breaths. The National Highway Traffic Safety Administration has published a Model Specification for breath alcohol ignition interlock devices which attempt to quantify some of the necessary operating parameters for such system. See 57 Fed. Reg. 11772 (#67), April 7, 1992.

Obtaining the accuracy criteria has been illusive. Vapor sensors of the type typically used in alcohol sensors, which vary their resistance in response to the presence of organic vapors, including alcohol vapors, have been found to be subject to random resistance variations due to temperature, humidity, unit-to-unit manufacturing tolerances, and variations in the condition and responsiveness of the reactive surface area resulting from the required repeated cleaning cycles utilized to maintain sensor sensitivity and operability. The ability to differentiate between a valid human breath and artificial inputs, as well as to identify human breaths which, due to their characteristics, may not provide a proper sample has also been difficult to meet. For example, it is important that the breath sample comprise alveolar air, which most closely tracks blood alcohol level. The breath must be of sufficient duration and depth to offer such air to a sensor system. Complex systems, relying on combinations of temperature, humidity and the like have often failed to provide sufficient accuracy of identification to insure meaningful results.

Brief Description of the Invention

It is accordingly a purpose of the present invention to provide a breath sensor apparatus, and particularly a breath alcohol sensor apparatus, which exhibits high reliability in identifying an input as a true human breath, and quantifying the level of a sensed breath component.

It is a further purpose of the present invention to provide a breath sensor apparatus which may be presented in a small and compact housing which may, for example, be easily accommodated in the hand of a user.

Still another purpose of the present invention is to provide a breath sensor apparatus of high accuracy and of compact and rugged construction which avoids the necessity for re-calibration or periodic cleansing cycles. Yet another purpose of the present invention is to provide a breath sensor apparatus which provides a feedback signal to the user to assist the user in providing a usable breath sample.

In accordance with the foregoing and other purposes, a breath sensor unit of the present invention incorporates a solid-state sensing module which utilizes optical characteristics sensitive to the presence of a particular substance, such as ethanol , in a sample to generate an electrical output signal. A characteristic of the output is proportional to the concentration of the sensed substance. The sensing module is located in a small, lightweight housing having an input air passageway. A first branch off the passageway leads to the sensor module. A second branch of the passageway within the housing leads to a pressure transducer. The outputs of the sensor module and pressure transducer are coupled to appropriate analysis and processing circuitry located remote from the housing. The housing further includes a sonic signalling device coupled to the processing circuitry to provide instructional cues to the user for operation of the breath sensor unit.

Brief Description of the Drawings

A fuller understanding of the present invention will be obtained upon consideration of the following detailed description of a preferred, but nonetheless illustrative, embodiment of the invention when reviewed in association with the annexed drawings, wherein:

FIG. 1 is a plan view of a hand-held breath sensor unit of the present invention;

FIG. 2 is a pictorial representation of the orientation of the functional elements of the invention within the housing;

FIG. 3 is a schematic representation of the functional elements; and

FIG. 4 is a block diagram of the invention and associated system elements.

Detailed Description of the Invention

The present invention incorporates the use of a solid-state sensor responsive to the presence of a particular sample constituent, and in particular ethyl alcohol, in the breath of a user. The preferred sensor is a fiber optic element in the form of a waveguide which directs and divides a beam of light between and along sampling and reference paths within the waveguide. The sampling path of the waveguide is provided with an optical coating, the characteristics of which vary as it interacts with the constituent of interest in the sample, thus affecting the light transmission properties of the waveguide. By comparison of the sampling and reference light beams a determination can be made as to the concentration of the constituent to which the sampling waveguide has been exposed. Such sensors are preferably constructed in accordance with the teachings of U.S. Patent Nos. 5,439,947 for a Chip Level Waveguide Sensor and U.S. Patent No. 4,846,548 for Fiber Optic Which Is An Inherent Chemical Sensor.

A waveguide sensor of the aforementioned type may be further fabricated as known in the art into a module with appropriate semiconductor circuitry to both drive the sensor and generate and condition appropriate output signals. Such circuitry, as known in the art, and as may be provided by Texas Instruments of Dallas, Texas may incorporate voltage-to-frequency convertors in which sampled and reference output signals generated by opto-electrical elements take the form of varying frequency wavetrains, the frequencies of which may be compared to obtain a quantitative measure of the level of the sensed constituent, such as ethanol, in the sampled stream.

In accordance with the foregoing and the present invention, and as depicted in FIGs. 1 and 2, solid-state sensor assembly 10 is mounted in a housing 12 which may be of compact design, capable of being held in the hand. Housing 12 has an input breath passageway 14 terminating at the exterior of the housing through nozzle 16. Preferably the nozzle 16 may be interchangeable to allow use of the device by a plurality of users.

As seen in FIG. 2, the sensor assembly 10 may preferably include waveguide sensor system 18, fabricated in the form of an integrated circuit assembly including ancillary circuit elements mounted on a printed circuit board 20. Also mounted to the board is a pressure transducer 22 and a sonic signalling device 24. A connector block 26 provides the necessary electrical connections between the elements and a cable 28, seen in FIG. 1, which couples the sensor assembly to a remote processor. The waveguide sensor system 18 is within a chamber 40, the wall of which may be fabricated as part of the interior of housing 12. Both the chamber 20 and the pressure transducer 22 are provided with coupling passageways 32, 34 respectively to provide entry for a breath sample.

Referring to FIG. 3, the input breath passageway is provided with a spit trap 30 proximate the nozzle to trap excess breath moisture and to prevent such moisture from passing through the passageway to the sensing components. The spit trap may be in the form of a fine mesh across the passageway. The passageway then divides into first and second branch passageways 36, 38. First branch passageway 36 leads to the waveguide sensor system chamber 40, through input tube 32. The chamber is provided with a vent 42 to permit a continuous flow of a breath sample to pass through the chamber and thus across the waveguide sensor system.

The second branch passageway 38 leads to a proportional pressure transducer 22 through coupling passageway 34. As known in the art, one side of the pressure-sensitive element of transducer 22 may define a portion of the interior surface of the transducer's internal sample reception chamber, while the opposite side of the pressure-sensitive element is exposed to ambient pressure within the housing. Pressure differences across the transducer generate an output electrical signal proportional to the pressure difference. For purposes of the present invention, the deviation in pressure of the breath sample over atmospheric may be in the range of .1 to .3 psi, and is chosen to be generally indicative of a sufficiently deep human breath from which a valid alcohol analysis can be performed.

Power for the components within the housing 12 may be provided through the cable 28 affixed to connector 26. Connector 26 also leads the signals developed by the waveguide sensor system 18 and the pressure transducer 22 to an appropriate processor, which in the automotive environment may preferably be located behind or below the dashboard. A sonic signalling element 24 is mounted on printed circuit board 24, positioned to allow its signal to be perceived by the user. The sonic signalling element is intended to provide a feedback function to the user in connection with breath sampling, and to provide other aural indications associated with system operation. Branch passageway 36 preferably is provided with a reduced diameter aperture or orifice 44 located proximate the entrance to the chamber 40. The orifice creates a back pressure through the breath passageways when a breath is applied, allowing such pressure to be sensed by pressure transducer 22. The orifice may be, for example, 1.6 mm in diameter in a passageway system of 6.4 mm diameter. Chamber exhaust port 42 is of large diameter which insures adequate evacuation of the chamber without development of significant additional backpressure therein and a continuing flow of breath therethrough. The volume of the chamber is such that it closely conforms to the geometry of the waveguide sensor system enclosed therein, providing a minimal volume allowing its contents to be replaced several times during the introduction of a breath sample.

As seen in FIG. 4, waveguide sensor system 18, pressure transducer 22 and sonic signalling element 24 are coupled to remote processor 48 through the cable 28. The processor 48, which may be microprocessor based, is further coupled to interlock module 46 which serves as an interface to the vehicle, providing the ignition cut-off, power connections, and other necessary interconnections. In operation, the user is prompted for a breath sample by the processor, either by the generation of a tone by the sonic signalling element or by another appropriate signal. The housing is brought to the mouth, the nozzle 16 being placed against the lips to allow the passageway 14 to be directly coupled to the mouth. The output of pressure transducer 22 reflects the internal pressure of the breath passageway 14 , and is passed to processor 48 which monitors the sensed pressure and activates sonic signalling element 24 for so long as the sensed pressure is above the baseline required for a valid breath sample, providing an indication t the user that he is providing a proper breath. The sonic signalling element is activated for so long as a proper pressure is maintained, the processor timing the length of the breath to insure the generation of a valid sample necessary for waveguide sensor unit 18 to have an adequate breath volume for an accurate alcohol measurement. Such a time may be on the order of six seconds. It has been found that the combination of a pressure differential coupled with a several second flow through a passageway system as presented herein makes it extremely difficult for an artificial breath sample to be used in an effort to defeat the monitoring apparatus.

When the test period has successfully been completed, a double beep tone is generated by the sonic signalling element, advising the user that a valid breath sample has been received. If the continuous tone stops without a confirmation signal the user knows that the breath sample provides is not sufficient, and a new breath will be required. A new breath request signal can then be generated. The continuous tone thus provides oral feedback for the user, providing timing for the ^' breath sample and confirming that he or she is providing a sufficiently deep breath for monitoring purposes. With receipt of a valid breath sample, processor 48 can accept for analysis the output of the waveguide sensor unit 18, activating the vehicle's ignition circuit if the alcohol level is below a preset value, and/or generating other commands and signals as required or desired.

The breath sensor system of the present invention, utilizing an alcohol sensor having no moving parts and which does not require an integral heater, is characterized by has zero warm-up time, as highly rugged configuration, and consistent results. Its high accuracy, and ease of use, coupled with its small size, allow an efficient breath alcohol sensing system, as well as other sensing systems capable of detecting other breath constituents, to be employed.

Claims

We claim:

1. An apparatus for measuring the concentration of a human breath constituent, comprising a hand-held housing; an internal breath passageway within said housing, said passageway having a first end through a nozzle mounted to the housing; a chamber within said housing coupled to said passageway; a waveguide sensor for detecting the constituent mounted in said chamber; a pressure transducer coupled to said passageway for measuring the pressure therein; a sonic signalling element mounted in said housing for generation of indicator sounds perceptible outside the housing; and electrical coupling means in said housing for coupling said waveguide sensor, pressure transducer and sonic signalling element to a remote processor.

2. The apparatus of claim 1 wherein said chamber has a wall formed integral with an interior portion of said housing.

3. The apparatus of claim 1 wherein said waveguide sensor is a waveguide sensor responsive to the presence of ethanol.

4. The apparatus of claim 1 further including a backpressure-generating orifice in said passageway proximate said chamber.