Infrared gas analyzer and method

• US 5,585,635 A
• Filed: 09/26/1994
• Issued: 12/17/1996
• Est. Priority Date: 09/26/1994
• Status: Expired due to Fees

• Current Assignee: Marquette Electronics (General Electric Company)
• Original Assignee: Marquette Electronics (General Electric Company)
• Inventors: Graham, James E.
• Primary Examiner(s): FIELDS, CAROLYN
• Application Number:
  US08/312,114
• Time in Patent Office: 813 Days
• Field of Search: 250/343, 250/338.5
• US Class Current: 250/343
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

An infrared gas analyzer and method employing one optical path which includes one infrared source, one sample cell containing the gas(es) to be analyzed, one infrared sensor and one infrared filter no matter how many gases are to be analyzed. The one optical path with one filter is utilized for both determining infrared source output and infrared absorption by the gas(es) to be measured.

Claims

1. A gas analyzer for analyzing a sample for a gas of interest, said analyzer comprising:

an infrared energy source;

a sensor for detecting infrared energy from said source, said infrared energy traveling between said source and said sensor defining an optical path;

a sample cell in said optical path comprising means for containing the sample to be analyzed;

at least two reference cells supported for selective positioning in said optical path,

an infrared filter in said optical path, said filter being a wideband filter passing the absorption spectra of the gases of interest and additional spectra on each side of the absorption spectra of the gases of interest;

said sensor producing a signal representative of the energy remaining when each of said reference cells are alternately in said optical path;

means for determining the power output of the infrared energy source using the additional spectra passed by said filter; and

a processor connected to said sensor whereby said processor receives said signals from said sensor and produces an output indicative of the concentration of the gas of interest in said sample cell.

2. A gas analyzer as set forth in claim 1 and further including a rotatable housing for supporting said reference cells so that said reference cells are selectively interposed in said optical path.

3. A gas analyzer as set forth in claim 2 and further including a motor connected to said housing for rotating said housing.

4. A method for analyzing a sample for multiple gases comprising the steps:

(a) supplying a path of infrared energy produced by an infrared energy source;

(b) interposing in said path a sample cell containing the sample to be analyzed;

(c) interposing in said path one wideband and infrared filter that passes the absorption spectra of the multiple gases and additional sidebands;

(d) detecting the infrared energy of said path after passage through said sample cell and said filter;

(e) using said additional sidebands to determine the infrared energy source power output;

(f) interposing in said path one of a plurality of reference cells, each reference cell containing a known quantity of a predetermined gas;

(g) detecting the infrared energy of said path after passage through said sample cell, said reference cell and said filter;

(h) producing a signal representative of said detected infrared energy of step (g); and

(i) interposing the remainder of said plurality of reference cells one at a time in said path and repeating steps (g)-(h); and

(j) processing said signals to determine whether and in what concentration the multiple gases are present in the sample.

5. A method for analyzing a sample for multiple gases as set forth in claim 4 in that the plurality of reference cells in step (f) equals one more than the number of multiple gases to be analyzed.

6. A method for analyzing a sample for multiple gases as set forth in claim 4 in that the sample cell of step (b) is downstream of the plurality of reference cells of step (f) in the path and the filter of step (c) is downstream of the sample cell of step (b) in the path.

7. A method for analyzing a gas mixture for gases of interest, said method comprising the steps:

(a) producing a beam of infrared energy from an infrared energy source;

(b) positioning in said beam a sample cell containing the gas mixture;

(c) positioning in said beam an infrared filter that passes a greater bandwidth of energy than the absorption spectra of the gases of interest;

(d) detecting the remaining infrared energy after said beam passes through said sample cell and said filter;

(e) determining the infrared energy source power output based upon the detected energy in step (d);

(f) positioning one of a plurality of reference cells in said beam, each of said reference cells filled with a known quantity of a predetermined gas;

(g) detecting the remaining infrared energy after said beam has passed through said sample cell, said reference cell and said filter;

(h) generating a signal representative of the detected remaining energy of step (g);

(i) positioning the others of said plurality of reference cells one at a time in said path and repeating steps (g)-(h); and

(j) determining the presence and concentration of the gases of interest using negative filtering with the signals generated in step (h) and with the infrared energy source power output from step (e).

8. A method for analyzing a gas mixture for gases of interest as set forth in claim 7 wherein said plurality of reference cells is one more than the number of multiple gases to be analyzed.

9. A method for analyzing a gas mixture for a gas of interest, said method comprising the steps:

(a) producing a beam of infrared energy from an infrared energy source;

(b) positioning in said beam a sample cell containing the gas mixture;

(c) positioning in said beam an infrared filter that passes the absorption spectra of the gas of interest and that additionally passes two sidebands of energy;

(d) using said sidebands to determine the infrared energy source power output;

(e) alternately positioning each of a plurality of reference cells in said beam, each of said plurality of reference cells containing a known quantity of a predetermined gas;

(f) detecting the level of the infrared energy of said beam after it passes through said sample cell, said filter and alternately each of said reference cells; and

(g) processing said detected levels from step (f) and said infrared energy source power output to determine the presence and concentration of the gas of interest.