Apparatus and method for the determination of the relative proportions of gases

• US 6,202,468 B1
• Filed: 01/13/1999
• Issued: 03/20/2001
• Est. Priority Date: 01/14/1998
• Status: Expired due to Term

• Current Assignee: Life Measurement Instruments
• Original Assignee: Life Measurement Instruments
• Inventors: Payne, John, Dempster, Philip
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): Politzer, Jay L.
• Application Number:
  US09/229,194
• Time in Patent Office: 797 Days
• Field of Search: 73/232, 73/240.1, 702/24, 204/425, 204/426, 204/427, 422/98, 374/117
• US Class Current: 73/23.2
• CPC Class Codes: G01N 2291/0215 Mixtures of three or more gases, e.g. air
• CPC Class Codes: G01N 2291/0217 Smoke, combustion gases
• CPC Class Codes: G01N 2291/02809 Concentration of a compound, e.g. measured by a surface mass change
• CPC Class Codes: G01N 29/024 by measuring propagation velocity or propagation time of acoustic waves
• CPC Class Codes: G01N 33/497 of gaseous biological material, e.g. breath

Abstract

The present invention relates to a method of determining the relative proportions of gases in a mixture, such that the relative proportions of N gases are determined using N-1 sensors, not all of which are specific to a particular gas. In the preferred embodiment, oxygen and carbon dioxide are measured in the presence of nitrogen by measuring magnetic susceptibility and speed of sound. The described method of gas analysis leads to very fast response times and exceptional stability, making the technology suitable for breath-by-breath analysis of respired air. Notably, the method does not require high-temperature components, electrochemical cells, or consumable components.

Claims

1. An apparatus for determining the relative proportion of gases within a gas mixture of three or fewer gases, including oxygen and carbon dioxide, the apparatus comprising:

means for determining the physical or chemical measure of the oxygen within a gas mixture to form a first measurement using a constantly applied magnetic field,

means for determining the speed of sound within the gas mixture to form a second measurement, and

means for determining the proportion of the carbon dioxide by numerical calculation from the first and second measurements.

2. The apparatus as in claim 1 including

means for rapidly alternating a reference gas and a test gas through the apparatus,

means for analyzing the resultant outputs for differences between the test and reference gas, and

means for creating essentially continuous measurement streams based on these differences.

3. The apparatus as in claim 2 in which the oxygen measure is by paramagnetic measure.

4. The apparatus as in claim 3 including an oxygen measuring head and a speed of sound measuring head with a common measuring chamber.

5. The apparatus as in claim 4 in which the chamber is in the form of an annulus with a plurality of ports, two of which serve as an inlet and outlet for the gases, and two of which serve as inlet and outlet for sound transducers.

6. The apparatus as in claim 3 in which the oxygen measuring head and the speed of sound measuring head are arranged serially in a single measurement path.

7. The apparatus as in claim 3, in which alternation of the sample and reference gases is by periodic operation of one or more valves, and in which a pneumatic compliance is arranged between the two valve inlets.

8. The apparatus as in claim 3, in which gas is drawn through the apparatus by a low pressure source which includes a biased vacuum regulator, whose reference input is connected to one of the gas inlets.

9. An apparatus as in claim 3, in which the temperature of the sensor head is monitored and the monitored temperature is used in the calculation of the detected signals.

10. The apparatus as in claim 3, in which the absolute pressure in the sensor head is monitored and the monitored pressure is used in the calculation of the detected signal.

11. The apparatus as in claim 3 in which the resultant outputs are each synchronously multiplied by a periodic signal of the same frequency as the alternation of test and reference gases, to produce a detected signal based on differences between the test and reference gases.

12. The apparatus as in claim 3 in which the control means includes means for gathering data over a time period, calculating the detected signals over a multiplicity of phase relationships between the gas alternation and the periodic signal used in detection, and choosing and storing those phase relationships for each gas which give a maximum output for future use in the detection system.