Breath sampling methodology having improved reliability

An improved method of breath sampling, particularly adapted for use in connection with motor vehicle alcohol breath monitoring devices, comprises the sending of a drive signal to a piston pump to draw a breath sample into a sensing chamber, the pump being connected to the sensing chamber. The operational status of the pump is monitored by monitoring the condition of a switch associated with the pump which is adapted to change state when the pump piston is withdrawn into its pump housing as a proper reaction of the pump to its drive signal and return to its original state when the pump piston is no longer withdrawn. The state condition of the of the switch is used to confirm proper pump operation in drawing the breath sample into the chamber; if proper pump operation is confirmed, the breath sample can be accepted for further processing and analysis.

The present invention relates to breath sensing equipment and particularly such equipment that employs a sensing chamber and a pump for drawing a breath sample into the chamber.

BACKGROUND OF THE INVENTION

There is currently great interest in employing devices to curb, monitor and control the use and operation of equipment, and particularly motor vehicles, by those under the influence of alcohol. Current technology provides devices that obtain breath samples of a driver, measure the concentration of alcohol in the breath sample, correlate that concentration to a blood alcohol concentration (BAC) and use the determined value to monitor the driver's condition and control his ability to operate the vehicle. Often the sensor system is connected to an interlock for the vehicle to prevent the vehicle from being started if the BAC is over a certain level, or to issue a warning if the vehicle is already in operation.

To insure consistency of breath samples, systems often use a small pump to pull a breath sample into the sensing chamber where the alcohol concentration is measured. The pump is usually a solenoid pump, which is prone to failure. If the pump fails, a proper breath sample is not drawn into the chamber, and accordingly the output of the alcohol sensor is not an accurate reflection of the condition of the user's breath sample intended to be obtained.

It is accordingly the purpose of the present invention to provide a method of monitoring the operation of such a solenoid pump to insure proper operation and thus the proper receipt of a breath sample by the breath sampling and sensing system. A further purpose of the invention is to provide such a method that can interface with other aspects of the sensing procedure to improve the reliability and performance thereof.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with the foregoing, the methodology of the present invention encompasses the use of a mechanical element, such as a pin, which is coupled to the piston of the pump that draws the breath sample into the sensing chamber. When the pump operates properly the piston retracts fully into its housing, allowing the pin to activate a switch, the condition of which indicates the status of the pump and accordingly whether a proper breath sample has been drawn into the sensing chamber. When combined with other signals derived from the drawing of a breath, such as a pressure reading, a better indication of the proper operation of the sensing system can be obtained and used to avoid inaccurate readings or attempts to foil the system.

DETAILED DESCRIPTION OF THE INVENTION

As seen in the figure, pump10is of the solenoid type, with piston12located for reciprocating motion within housing14. Withdrawal of the piston within the chamber is accomplished by activation of solenoid coil16surrounding solenoid core18and the housing by an appropriate electrical signal, typically controlled by the microprocessor controller for the sensing unit.

The pump's chamber is connected to sensing chamber20by tube22. A second tube24leads from the sensing chamber to a breath sample input device, such as a hand-held mouthpiece. When the pump is activated, the core and piston retract and a breath sample is drawn into the sensing chamber from the sample input. The volume of the pump's chamber, in association with the degree of piston travel, controls the volume of the breath sample that is drawn into and through the sensing chamber, and are chosen to ensure that a sufficient breath volume is drawn for a proper analysis. In coordination with the operation of the pump an electrical sensing means in the sensing chamber measures the alcohol level of the drawn sample in accordance with known principles and methods. Once the sample is measured, power to the solenoid is cut off, the pump piston returning to the rest position through the action of return spring26, exhausting the sample from chamber. Tubes22and24may include appropriate valuing to ensure proper breath flow.

Pin28is mounted to the core in a manner such that, when the pump piston is fully drawn back by solenoid action, corresponding to the successful operation of the pump to draw a breath sample into the sensing chamber, it engages switch30, which typically has two states. The change of state resulting from engagement by or with the pin causes the switch to change state. The change of state is transmitted to the microprocessor, thus confirming to the microprocessor the proper operation of the pump. The lack of a confirming signal once an operating signal for the solenoid has issued indicates a malfunction of pump, which can be acted on as appropriate by the microprocessor. The confirmation may be affirmatively used by the microprocessor to validate the contents of the sensing chamber as a valid breath sample, allowing the sensor output to be accepted and further steps in the analysis and operation of the sensing system to proceed.

In a like manner, when return of the piston to the rest position occurs, the corresponding state change of the switch may be monitored by the microprocessor to confirm that the pump is ready to accept a new breath sample. A failure of the piston to return to the ready position maintains engagement between the pin and switch, preventing the state change required by the microprocessor.