Method and apparatus for real time gas analysis

• US 6,250,132 B1
• Filed: 12/21/1999
• Issued: 06/26/2001
• 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:
  US09/468,792
• Time in Patent Office: 553 Days
• Field of Search: 73/232, 73/240.5, 73/240.1, 73/530.1, 73/614.3, 73/614.4, 73/615.2, 73/644.5, 73/233.5, 73/232.2, 732/042.1, 738/616.1, 738/616.3, 738/611.9, 73/541.1, 73/530.4, 73/232.4, 73/232.7, 422/82, 422/84, 422/68.1, 340/603, 340/632, 137/91-93, 137/835
• 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 modular apparatus for analyzing a fluid includes a disposable fluidic sensor module, a replaceable transducer module, and an expendable electronics package. The disposable fluidic sensor includes a fluidic flowmeter and a capillary structure formed in a plate-like member which receives a sample fluid flow. The fluidic flowmeter is responsive to the fluid flow to generate an output indicative of the flow rate of the fluid, and the capillary structure restricts the fluid flow such that a pressure drop across the capillary structure is related to the viscosity of the fluid. The fluidic flowmeter can be a fluidic oscillator whose oscillation frequency is related to the fluid flow rate. The oscillator flowmeter also serves as an orifice, with the pressure drop across the oscillator being related to the density of the fluid. The replaceable transducer module is connectable to the fluidic sensor module via a separable interface, and includes transducers for measuring physical conditions of the fluid flowing through the fluidic sensor module. The expendable electronics package includes a processor responsive to transducer signals generated by the transducers for determining properties and conditions of the fluid, such as flow rate, density and viscosity, and for determining individual concentrations of fluid constituents of the fluid from these parameters.

Claims

1. A disposable fluidic sensor module for an apparatus for analyzing a fluid, the disposable fluidic sensor comprising:

a plate-like member having an inlet adapted to receive a flow of the fluid and an outlet for exhausting the flow of the fluid;

a fluidic flowmeter formed in said plate-like member in a path between the inlet and the outlet, said fluidic flowmeter being responsive to the flow of the fluid to generate an output indicative of a flow rate of the fluid;

a capillary structure formed in said plate-like member in a path between the inlet and the outlet, said capillary structure restricting a flow of the fluid such that a pressure drop across said capillary structure is related to a viscosity of the fluid; and

a sonic oscillator formed in said plate-like member in a path between the inlet and the outlet, said sonic oscillator generating flow oscillations having a frequency related to the specific heat of the fluid.

2. A modular apparatus for analyzing a fluid, comprising:

a disposable fluidic sensor module comprising;

a plate-like member having an inlet adapted to receive a flow of the fluid and an outlet for exhausting the flow of the fluid;

a fluidic flowmeter formed in said plate-like member in a path between the inlet and the outlet, said fluidic flowmeter being responsive to the flow of the fluid to generate an output indicative of a flow rate of the fluid, and a capillary structure formed in said plate-like member in a path between the inlet and the outlet said capillary structure restricting a flow of the fluid such that a pressure drop across said capillary structure is related to a viscosity of the fluid;

a replaceable transducer module connectable to said fluidic sensor module via a separable interface, said replaceable transducer module comprising transducers for measuring physical conditions of the fluid flowing through said fluidic sensor module;

an expendable electronics package connectable to said replaceable transducer module, said expendable electronics comprising a processor responsive to transducer signals generated by said transducers for determining properties of the fluid; and

a sonic oscillator formed in said plate-like member in a path between the inlet and the outlet, said sonic oscillator generating flow oscillations having a frequency related to the specific heat of the fluid.

3. A disposable fluidic sensor module for an apparatus for analyzing a fluid, the disposable fluidic sensor comprising:

a plate-like member having an inlet adapted to receive a flow of the fluid and an outlet for exhausting the flow of the fluid;

a fluidic oscillator formed in said plate-like member in a path between the inlet and the outlet and having a period of oscillation substantially proportional to a transit time of the fluid from an input of the fluidic oscillator to an output of the fluidic oscillator, wherein the period of oscillation of the fluidic oscillator is substantially independent of the density and viscosity of the fluid, said fluidic oscillator being responsive to the flow of the fluid to generate an output indicative of a flow rate of the fluid; and

a capillary structure formed in said plate-like member in a path between the inlet and the outlet, said capillary structure restricting a flow of the fluid such that a pressure drop across said capillary structure is related to a viscosity of the fluid.

4. The disposable fluidic sensor module according to claim 3, wherein a pressure drop from an input of said fluidic oscillator to an output of said fluidic oscillator is related to a density of the fluid.

5. The disposable fluidic sensor module according to claim 4, wherein said fluidic oscillator is a fluidic amplifier feedback oscillator flowmeter.

6. The disposable fluidic sensor module according to claim 3, wherein said capillary structure comprises a plurality of capillaries arranged to provide parallel resistance to flow of the fluid through said capillary structure.

7. A replaceable transducer module for interfacing with the disposable sensor module of claim 3, comprising:

a temperature sensor for measuring the absolute temperature of the fluid passing through said disposable sensor module;

a pressure sensor for measuring the absolute pressure of the fluid passing through said disposable sensor module;

two differential pressure transducers for respectively measuring pressure drops across the fluidic oscillator and the capillary of said disposable sensor module;

a plurality of microphones for measuring oscillation frequencies in the fluidic oscillator of said disposable sensor module; and

a vacuum line connection configured to connect said disposable sensor module to a vacuum source to draw sample fluid through said disposable sensor module.

8. An expendable electronics package adapted to receive transducer signals generated by the replaceable transducer module of claim 7, comprising:

a multiplexer providing analog signals corresponding to signals received from said temperature sensor, said pressure sensor, and said two differential pressure transducers;

an analog-to-digital converter for converting the analog signals to digital signals;

a flow counter for generating a digital frequency signal in response to an output signal from said microphone; and

a microprocessor responsive to the digital signals and the digital frequency signal, for computing individual concentrations of constituents of said fluid.

9. A modular apparatus for analyzing a fluid, comprising:

a disposable fluidic sensor module comprising;

a plate-like member having an inlet adapted to receive a flow of the fluid and an outlet for exhausting the flow of the fluid;

a fluidic oscillator formed in said plate-like member in a path between the inlet and the outlet and having a period of oscillation substantially proportional to a transit time of the fluid from an input of the fluidic oscillator to an output of the fluidic oscillator, wherein the period of oscillation of the fluidic oscillator is substantially independent of the density and viscosity of the fluid, said fluidic flowmeter being responsive to the flow of the fluid to generate an output indicative of a flow rate of the fluid; and

a capillary structure formed in said plate-like member in a path between the inlet and the outlet, said capillary structure restricting a flow of the fluid such that a pressure drop across said capillary structure is related to a viscosity of the fluid;

a replaceable transducer module connectable to said fluidic sensor module via a separable interface, said replaceable transducer module comprising transducers for measuring physical conditions of the fluid flowing through said fluidic sensor module; and

an expendable electronics package connectable to said replaceable transducer module, said expendable electronics comprising a processor responsive to transducer signals generated by said transducers for determining properties of the fluid.

10. The modular apparatus according to claim 9, wherein said capillary structure comprises a plurality of capillaries arranged to provide parallel resistance to flow of the fluid through said capillary structure.

11. The modular apparatus according to claim 9, wherein a pressure drop from an input of said fluidic oscillator to an output of said fluidic oscillator is related to a density of the fluid.

12. The modular apparatus according to claim 11, wherein said replaceable transducer module comprises:

a temperature sensor for measuring the absolute temperature of the fluid passing through said disposable sensor module;

a pressure sensor for measuring the absolute pressure of the fluid passing through said disposable sensor module;

two differential pressure transducers for respectively measuring pressure drops across the fluidic oscillator and the capillary of said disposable sensor module;

a plurality of microphones for measuring oscillation frequencies in the fluidic oscillator of said disposable sensor module; and

a vacuum line connection configured to connect said disposable sensor module to a vacuum source to draw sample fluid through said disposable sensor module.

13. The modular apparatus according to claim 12, wherein said expendable electronics package comprises:

a multiplexer providing analog signals corresponding to signals received from said temperature sensor, said pressure sensor, and said two differential pressure transducers;

an analog-to-digital converter for converting the analog signals to digital signals;

a flow counter for generating a digital frequency signal in response to an output signal from said microphone; and

a microprocessor responsive to the digital signals and the digital frequency signal, for computing individual concentrations of constituents of said fluid.

14. 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 flowmeter 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.

15. The disposable fluidic module of claim 14 wherein said module is molded plastic, and wherein said flow channels and said capillary passages are molded in said module.

16. The disposable fluidic module of claim 14 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.

17. The fluidic module of claim 14 wherein said flowing medium is a gas having multiple gaseous constituents.

18. The disposable fluidic module of claim 14 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.