Measuring and testing – Gas content of a liquid or a solid
Utility Patent
1999-12-14
2001-01-02
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Gas content of a liquid or a solid
C073S023300, C422S084000, C436S132000, C436S900000, C340S576000, C180S272000
Utility Patent
active
06167746
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to devices and methods for determining the concentration of alcohol in a mixture of gases. More particularly, the invention relates to a device and method for determining the concentration of alcohol in a breath sample for application in sobriety detection systems and sobriety interlock systems for vehicles and other machines.
Various techniques have been employed for calculating a person's blood alcohol concentration by measuring breath samples. In a first method, the alcohol content in a breath sample is measured using a semiconductor sensor commonly referred to as a Tagucci cell. Although this method provides a low cost device, instruments incorporating this method have proved to have poor accuracy.
A second method employs an infrared absorption technique for determining the blood alcohol concentration. This method has proven to have very high accuracy levels. However, the sensor systems incorporating this technique are cost prohibitive for many applications.
A third method employs a fuel cell together with an electronic circuit. This method is described in U.S. Pat. No. 4,487,055. Although this method allows for more accuracy than the first method, the systems employing this method have continued to be relatively expensive. One reason for the high cost associated with the fuel cell techniques is that the method requires that the breath sample be of a determinable volume. Historically, this has been accomplished through the use of positive displacement components such as piston-cylinder or diaphragm mechanisms. The incorporation of such components within an electronic device necessarily increases the costs associated with the device.
The current invention departs from the use of the expensive positive displacement mechanisms while retaining the accuracy provided by the fuel cell. The current invention employs a valve controlled by a computing device such as a microprocessor to regulate the total volume of gas passing through the fuel cell.
SUMMARY OF THE INVENTION
According to the invention, a sobriety detection system obtaining relatively good accuracy at an acceptable cost is disclosed. In one embodiment, the alcohol concentration in a person's breath is determined by passing a breath sample of determinable volume through a fuel cell. The invention obtains a breath sample of determinable volume by electronically controlling a valve permitting breath flow into the fuel cell. A valve controller limits the duration of time the valve is open based upon the pressure of the breath flow. The fuel cell produces a voltage output proportional to the total volume of alcohol in the breath sample. A computing device determines the total volume of alcohol in the sample from the fuel cell voltage output. The computing device adjusts the valve-open time as a function of pressure to obtain a constant-volume breath sample. Therefore, the alcohol concentration is known directly from the fuel cell voltage by applying the appropriate scale factor.
In another embodiment, the invention is employed in a sobriety interlock device to prevent operation of a machine such as a vehicle, unless the operator's breath alcohol concentration is first determined to be below a predefined level. In this embodiment, the machine operator breathes into the interlock device incorporating the invention. The device then determines whether the alcohol concentration in the breath sample is below the acceptable level. If the concentration is acceptable, the interlock permits enablement of the machine ignition or power supply. If the concentration is above the permissible level, the interlock prohibits ignition or operation of the machine.
When used in an interlock device, the invention may incorporate additional elements and features to prevent an intoxicated person from defeating the interlock by introducing a sample from a source other than the operator's breath. The device may include a temperature sensor which will prohibit enablement of the machine unless the breath flow is within an acceptable range around human body temperature. The device may also incorporate logic within the computing device to prohibit enablement of the machine unless a pressure oscillation within the breath flow is detected. In the proper operation, the operator generates the pressure oscillation by humming while breathing into the device. The device may also enforce minimum and maximum blow-pressure limits to prevent the use of artificial samples and to detect the use of alcohol-removing filter media, such as activated charcoal, by detecting the resultant low pressure caused by pressure drop across the filter.
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Larkin Daniel S.
Smart Start Inc.
Wiggins J. David
Wynne, Jr. Richard L.
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