Method and apparatus for real time gas analysis

• US 6,305,212 B1
• Filed: 04/07/2000
• Issued: 10/23/2001
• Est. Priority Date: 08/18/1997
• Status: Expired due to Fees

• Current Assignee: Metasensors, Inc.
• Original Assignee: Metasensors, Inc.
• Inventors: Drzewiecki, Tadeusz M.
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): WIGGINS, JOHN DAVID
• Application Number:
  US09/545,669
• Time in Patent Office: 564 Days
• Field of Search: 730/23.2, 730/32 A, 730/24.01, 730/53.01, 730/54.02, 730/54.06, 730/54.09, 730/61.49, 730/61.61, 730/61.75, 730/61.79, 730/DIG. 8, 422/82, 422/93
• US Class Current: 73/23.2
• CPC Class Codes: A61M 16/0051 with alarm devices
• CPC Class Codes: A61M 16/021 operated by electrical means A61M16/202 – A61M16/205 take precedence
• CPC Class Codes: A61M 16/0808 Condensation traps
• CPC Class Codes: A61M 16/085 Gas sampling
• CPC Class Codes: A61M 2016/1025 the O2 concentration
• CPC Class Codes: A61M 2016/103 the CO2 concentration
• CPC Class Codes: A61M 2016/1035 the anaesthetic agent concentration
• CPC Class Codes: A61M 2230/432 partial CO2 pressure (P-CO2)
• CPC Class Codes: A61M 2230/435 partial O2 pressure (P-O2)
• CPC Class Codes: G01F 1/3227 using fluidic oscillators fluidic oscillators per se F15C1/00
• CPC Class Codes: G01N 2291/02872 Pressure
• CPC Class Codes: G01N 2291/02881 Temperature
• CPC Class Codes: Y10T 137/2234 And feedback passage[s] or path[s]
• CPC Class Codes: Y10T 137/2506 By viscosity or consistency

Abstract

A method and apparatus for real time gas analysis involving determining individual concentrations of fluid constituents in a mixture of known constituents by measuring properties of the mixture and solving a set of equations, which relate the individual gas concentrations to the measured properties of the mixture, for the unknown individual gas concentrations. The individual concentrations of four gasses in a mixture are determined by: passing the mixture through a flowmeter, a capillary, an orifice, and a sonic oscillator; transducing temperature, pressure and acoustic frequency measurements taken from the sensors; determining the density, viscosity, and the specific heat of the mixture; forming three equations which respectively relate these three properties to individual gas concentrations; and solving the three equations and the constitutive equation which requires that the sum of the concentrations equal unity, for the four unknown individual gas concentrations. A single oscillator can serve as both a sensor (e.g., flowmeter, acoustic velocimeter) and an orifice. The fluidic sensors can be formed as a single chip disposable sensor module. By modifying only the processing software, the same sensors or a subset of the sensors can be used to verify or determine the identity of an unknown gas which is supplied by itself in a pure form or in a mixture of other gasses whose identities are known. By measuring N−1 properties of the gas mixture as a whole, the capabilities of an existing sensor system for measuring M gas concentrations can be extended to measure N additional gas concentrations, provided the identities of the gasses in the mixture are known. Similarly, by modifying only the processing software the same sensor can be used to analyze any sets of gas mixtures.

Claims

1. A disposable fluidic module for sensing plural characteristics of a flowing medium, said module comprising:

an inlet port for receiving the flowing medium at said module;

a flow meter for receiving the flowing medium from said inlet port and configured in the form of a fluidic oscillator for transversely oscillating said flowing medium at an oscillation frequency that varies as a function of the velocity of said flowing medium, said fluidic oscillator being defined as a plurality of flow channels; and

a capillary member for receiving output flow from said fluidic oscillator and establishing a pressure drop in said output flow, said capillary member comprising a common flow entrance, a common flow exit and a plurality of capillary passages extending in flow communication between said entrance and exit, said capillary passages having transverse cross-sections that are very much smaller than transverse cross-sections of said flow channels in said fluidic oscillator;

wherein said module is a rigid member, and wherein said fluidic oscillator and said capillary passages are formed as flow passages defined in said rigid member.

2. The disposable fluidic module of claim 1 wherein said module is molded plastic, and wherein said flow channels and said capillary passages are molded in said module.

3. The disposable fluidic module of claim 1 wherein said rigid member includes at least one plastic molded body having a surface in which said capillary passages and said flow channels of said fluidic oscillator are defined as recesses.

4. The fluidic module of claim 1 wherein said flowing medium is a gas having multiple gaseous constituents.

5. The disposable fluidic module of claim 1 further comprising:

first and second ports defined in said rigid member, said first port being defined upstream of said fluidic oscillator, said second port being defined downstream of said fluidic oscillator to permit measurement of pressure drops in said medium across said first and second ports; and

third and fourth ports defined in said rigid member for permitting measurement of the pressure drops in said medium across said capillary member.