Method of identifying a gas and associated apparatus

• US 6,435,003 B1
• Filed: 11/08/2001
• Issued: 08/20/2002
• Est. Priority Date: 04/05/2000
• Status: Active Grant

• Current Assignee: Industrial Scientific Corporation (Fortive Corp.)
• Original Assignee: Industrial Scientific Corporation (Fortive Corp.)
• Inventors: Warburton, P. Richard
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): CYGAN, MICHAEL T
• Application Number:
  US09/986,306
• Publication Number:
  US 20020050161A1
• Time in Patent Office: 285 Days
• Field of Search: 73/10--, 73/232, 73/233, 73/644.7, 204/409, 204/415, 204/431, 205/782, 205/782.5, 205/783, 205/775, 205/779.5, 205/781, 205/786.5, 205/787, 205/793
• US Class Current: 73/23.2
• CPC Class Codes: G01N 13/00 Investigating surface or boundary effects, e.g. wetting power; Investigating diffusion effects; Analysing materials by determining surface, boundary, or diffusion effects scanning-probe techniques or apparatus G01Q
• CPC Class Codes: G01N 27/4045 for gases other than oxygen

Abstract

A method for identifying an unknown gas using a diffusion limited sensor providing an electrical signal output when exposed to the gas. According to the method, a sensor is disposed in a chamber of fixed volume and having a gas input and gas output through which the gas flows, and the chamber is connected to a source of a known test gas of known concentration and known diffusion coefficient D_k. The input to the chamber is opened, causing the sensor to be exposed to the known test gas until a steady state electrical signal output from the sensor is obtained. The time T_k necessary for the sensor to attain a predetermined percentage of the steady state output is determined. The chamber is then connected to a source of unknown gas, and the input is opened, and time T_u necessary for the sensor to attain the predetermined percentage of a steady state output for the unknown gas is determined. The diffusion coefficient D_u for the unknown gas is calculated by the formula D_u=D_k×(T_k/T_u); and the unknown gas is identified by its calculated diffusion coefficient.

Claims

1. A method for identifying an unknown gas using a diffusion limited sensor providing an electrical signal output when exposed to the gas, comprising the steps of:

disposing the sensor in a chamber of fixed volume and having a gas input and gas output through which the gas flows;

connecting the chamber to a source of a known test gas of known concentration and known diffusion coefficient D_k, opening the input to the chamber, and causing the sensor to be exposed to the known test gas until a steady state electrical signal output from the sensor is obtained;

determining the time T_k necessary for the sensor to attain a predetermined percentage of the steady state output;

closing the input to the chamber and disconnecting the chamber from the source of the known test gas;

connecting the chamber to a source of said unknown gas;

opening the input to the chamber and determining the time T_u necessary for the sensor to attain said predetermined percentage of a steady state output for the unknown gas;

calculating a diffusion coefficient D_u for the unknown gas by the formula D_u=D_k×

(T_k/T_u); and

identifying the unknown gas by its calculated diffusion coefficient.

2. The method of claim 1, wherein the predetermined percentage is 50%.

3. The method of claim 1, wherein the predetermined percentage is 90%.

4. The method of claim 1, wherein the sensor is an electrochemical sensor.

5. The method of claim 1, wherein the sensor is a catalytic bead sensor.

6. A method for identifying an unknown gas using a diffusion limited sensor providing an electrical signal output when exposed to the gas, comprising the steps of:

disposing the sensor in a chamber of fixed volume and having a gas input and gas output through which the gas flows;

connecting the chamber to a source of a known test gas of known concentration and known diffusion coefficient D_k, opening the input to the chamber, and causing the sensor to be exposed to a flow of the known test gas until a steady state electrical signal output from the sensor is obtained;

closing the input to the sensor and determining the time T_k2 necessary for the sensor to attain a predetermined percentage of the steady state output;

disconnecting the chamber from the source of the known test gas;

connecting the chamber to a source of said unknown gas;

opening the input to the chamber and exposing the sensor to a flow of unknown gas until a steady state output is attained;

closing the input to the sensor and determining the time T_u2 necessary for the sensor to attain the predetermined percentage of the steady state output for the unknown gas;

calculating a diffusion coefficient D_u for the unknown gas by the formula D_u=D_k×

(T_k2/T_u2); and

identifying the unknown gas by its calculated diffusion coefficient.

7. The method of claim 6, wherein the predetermined percentage is 50%.

8. The method of claim 6, wherein the predetermined percentage is 90%.

9. The method of claim 6, wherein the sensor is an electrochemical sensor.

10. The method of claim 6, wherein the electrochemical sensor is a catalytic bead sensor.

11. In a method for analyzing a gas comprising disposing a diffusion limited electrochemical sensor providing an electrical signal output when exposed to the gas in a chamber of fixed volume and having a gas input and gas output through which the gas flows, and exposing the sensor to a flow of the gas,

the improvement comprising identifying an unknown gas of diffusion coefficient D_u comprising determining time necessary T_u for the sensor to attain a steady state electrical output or predetermined fraction thereof upon exposure to the unknown gas, determining time necessary T_k for the sensor to attain said steady state electrical output or said predetermined fraction thereof upon exposure to a known gas of diffusion coefficient D_k, calculating a value for D_u according to the formula D_u=D_k×

(T_k/T_u), and identifying the unknown gas by the calculated value D_u.