Infrared breath analyzer with calibration provisions and related method

• US 5,422,485 A
• Filed: 07/09/1993
• Issued: 06/06/1995
• Est. Priority Date: 07/09/1993
• Status: Expired due to Fees

• Current Assignee: CMI Corporation (Terex Corporation)
• Original Assignee: CMI Corporation (Terex Corporation)
• Inventors: Bowlds, Harvey F.
• Primary Examiner(s): Hannaher, Constantine
• Application Number:
  US08/089,216
• Time in Patent Office: 697 Days
• Field of Search: 250/252.1 A, 250/343
• US Class Current: 250/343
• CPC Class Codes: G01N 2021/3174 Filter wheel
• CPC Class Codes: G01N 21/276 with alternation of sample and standard in optical path
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01N 33/4972 Determining alcohol content for vehicle safety devices B60K28/06

Abstract

A calibration device, method and apparatus is provided for checking calibration of a breath alcohol measuring instrument. A silicon wafer with an anti-reflective silicon monoxide coating on both sides is used to attenuate the infrared radiation in the range of 3.35 to 3.80 microns wavelength in a manner to simulate the attenuation caused by a breath sample containing 0.10 BrAC. A comparison of the signal generated by the attenuation at a wavelength of approximately 3.48 microns is made to the baseline signal obtained before placing the calibration disk in the IR beam path and accurately simulates the breath sample. The related breath alcohol measuring method and apparatus provides for the positioning of the composite disk in the path between the infrared source and receiver. A computer compares the signals and performs the calibration check, as well as the actual BrAC analysis.

Claims

1. A calibration device for a breath alcohol measuring instrument wherein alcohol content in a breath sample is calculated by measuring attenuation of infrared radiation along a radiation path comprising:

a disk substrate;

an anti-reflective coating on said substrate, the composition of said disk substrate and said coating attenuating the infrared radiation to provide simulation of a breath sample containing a known percent of alcohol.

2. The device as set forth in claim 1 wherein the composition of said substrate and said coating strongly attenuates infrared radiation at a wavelength of 3.48 microns to simulate a breath sample containing 0.10 percent breath alcohol.

3. The device as set forth in claim 2 wherein:

said disk substrate includes an approximately 2.5 mm thick silicon disk;

said anti-reflective coating comprises an approximately 5940 Å

thick silicon monoxide coating on both sides.

4. A method for calibration check of a breath alcohol measuring instrument having an infrared radiation source for emitting an infrared beam defining a radiation path to a receiver, a sample chamber along the path, and a computer, the method comprising the steps of:

providing a substrate with an anti-reflective coating for attenuating the beam;

storing a known alcohol content value characteristic of the substrate in the computer upon initial setup or calibration of the instrument;

passing the infrared beam through the substrate and anti-reflective coating for attenuating the infrared radiation of a wavelength of approximately 3.35-3.80 microns to simulate a breath sample with the known alcohol content;

receiving the attenuated radiation at said receiver;

computing the simulated value of alcohol concentration from the attenuation of the beam at the receiver; and

comparing the simulated value to the known alcohol concentration value to check proper calibration of the instrument.

5. The method as set forth in claim 4 wherein said receiving step further includes receiving only infrared radiation of a wavelength of approximately 3.48 microns that is strongly attenuated by breath alcohol.

6. A breath alcohol measuring instrument comprising:

a sealed sample chamber;

means for retaining a breath sample in said chamber;

means for purging with fresh air said sample from said chamber;

an infrared radiation source and receiver and a radiation path defined therebetween including within said chamber;

means for filtering the infrared radiation beam so that only infrared radiation of at least one specific wavelength is received at said receiver, the radiation of said wavelength being strongly attenuated by breath alcohol;

a composite disk for positioning in said path including a substrate coated with an anti-reflective coating for simulating a breath sample with a known alcohol content by causing attenuation of the infrared radiation at said wavelength; and

computer means for storing a known alcohol content value of the disk upon initial set-up or calibration of the instrument and for determining the simulated attenuation as provided by passing the beam through said disk;

said computer means being further operative for comparing the known attenuation to said simulated attenuation to check the calibration and for determining actual alcohol content when a breath sample is present in said chamber;

whereby the proper calibration of said instrument can be verified and an accurate determination of breath alcohol can be made by said instrument.

7. The instrument as set forth in claim 6 further including means for positioning said composite disk into and out of said path for checking the calibration comprising:

a stepper motor having output shaft; and

a mounting arm carrying said disk and operatively connected to the output shaft of said stepper motor so that upon activation of said stepper motor by said computer said disk is oscillated into said radiation path.

8. The instrument as set forth in claim 6 wherein said means for filtering includes a first filtering means for filtering out of said radiation beam all wavelengths except at approximately 3.48 microns, which wavelength is strongly attenuated by passing through said disk.

9. The instrument as set forth in claim 8 wherein said means for filtering includes a second filtering means operative for all wavelengths except at approximately 3.8 microns, which wavelength is not attenuated by said disk;

means to alternately introduce said first and second filtering means into said path;

whereby the alternate radiation values are determined for comparison by said computer.

10. The instrument as set forth in claim 9, wherein is provided a wheel for supporting said first and second filtering means;

means for rotating said filter wheel to alternately introduce said filtering means into said path.

11. The instrument as set forth in claim 6 wherein said composite disk includes:

an approximately 2.5 mm thick silicon substrate; and

an approximately 5940 Å

thick silicon monoxide coating on both sides of said silicon wafer.