Apparatus and method for determining a person's sobriety

DETAILED DESCRIPTION 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