Patent ID: 7422723

Claim:
A breath alcohol detection device comprising: A) a breath inlet passage having an inlet port; B) a pressure sensor in communication with the breath inlet passage to generate a pressure signal responsive to the pressure in the breath inlet passage; C) a fuel cell; D) a vent passage communicating the breath inlet passage to the atmosphere; E) a two position valve having a valve inlet connected to the breath inlet passage between the inlet port and the vent passage, first and second valve outlets, a valve member moveable from a first position connecting the valve inlet to the first outlet and disconnecting the valve inlet from the second valve outlet and a second position connecting the valve inlet to the second valve outlet and disconnecting the valve inlet from the first valve outlet, wherein the valve inlet is always connected to only one of the valve outlets depending upon the position of the valve member; F) a first passage extending from the first valve outlet to atmosphere, and a first restriction in such passage; G) a second passage extending from the second valve outlet to atmosphere through the fuel cell, and a second restriction in such second passage, said first restriction generally equaling said second restriction; and H) an actuator for shifting the valve member from the first position to the second position for a short interval to flow a volume of breath from the breath inlet passage through the valve, along the second passage and into the fuel cell to generate a fuel cell output signal proportional to the alcohol contained in the volume of breath, the actuator normally maintaining the valve member in the first position, wherein a portion of breath flowed through the breath inlet passage continuously flows through the valve and only one of said first or second passages and one of the restrictions so that the pressure in the breath inlet passage does not substantially vary when the valve member shifts between the first and second positions.