Gas analyzer

• US 4,233,513 A
• Filed: 10/05/1978
• Issued: 11/11/1980
• Est. Priority Date: 10/05/1978
• Status: Expired due to Term

• Current Assignee: AC Limited (Emirate of Dubai (United Arab Emirates))
• Original Assignee: Andros, Inc. (Advanced Energy Industries, Inc. (China))
• Inventors: Williams, Kevin G., Burough, Irvin G., Elder, William L.
• Primary Examiner(s): Willis, Davis L.
• Assistant Examiner(s): Howell, Janice A.
• Application Number:
  US05/948,674
• Time in Patent Office: 768 Days
• Field of Search: 250/343, 250/344, 250/346, 250/351, 250/352
• US Class Current: 250/343
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

A gas analyzer of the non-dispersive infrared type is described. An infrared beam passing through a sample cell containing a gas mixture to be analyzed is detected. The resulting electrical signals are processed to produce an output indicating the concentration of the constituents of the gas mixture in the sample cell. The gas analyzer includes provision for temperature stabilizing both a rotary filter wheel and the detector, and for compensating the output of the signal processor for variation in the absorption characteristics of gas with temperature. The emissivity characteristic of the infrared energy source substantially compensates for wavelength dependence of the detector response. The motor drive for the rotary filter wheel is servo-controlled in accordance with synchronizing pulses developed directly from the detector output.

Claims

1. A gas analyzer comprising, a sample cell for containing gas to be analyzed, means for producing and directing infrared energy through said sample cell, means for detecting the infrared energy passing through said sample cell and producing an electrical signal representative thereof, means coupled to said detecting means for processing the electrical signal to produce an output indicating the concentration of the constituents of the gas in said sample cell, a rotary filter wheel for successively and repetitively positioning at least one filter in the path of the infrared energy, a housing enclosing said filter wheel exclusive of said sample cell and said detecting means, means for maintaining the temperature in said housing at a substantially constant level, said signal processing means including means for compensating the output thereof for variation in the absorption characteristic of gas with temperature.

2. A gas analyzer according to claim 1 wherein said detecting means include a lead-selenide detector, and wherein said infrared energy producing and directing means include an infrared energy source having an emissivity characteristic which varies such as to substantially compensate for wavelength dependence of the response of lead-selenide.

3. A gas analyzer according to claim 1 including means coupled to said detector means for deriving a series of synchronizing pulses related to variations in the electrical signal produced by said detector means, and servo-control means controlling the speed of said rotary filter wheel in accordance with said synchronizing pulses.

4. A gas analyzer according to claim 2 including thermoelectric means for maintaining the temperature of said detector means at a preselected level, means for sensing the temperature of said detector means, and bidirectional power supply means for said thermoelectric means responsive to said temperature sensing means for causing said thermoelectric means to heat or cool said detector means in relation to ambient temperature.

5. A gas analyzer according to claim 1 wherein said compensating means include temperature sensitive resistor means for varying the gain of said signal processing means.

6. A gas analyzer according to claim 1 wherein said compensating means include temperature sensitive resistor means for varying the calibration of said signal processing means.

7. A gas analyzer, comprising, a sample cell for containing gas to be analyzed, means for producing and directing infrared energy through said sample cell, lead-selenide detector means for detecting the infrared energy passing through said sample cell and producing an electrical signal representative thereof, means coupled to said detector means for processing the electrical signal to produce an output indicating the concentration of the constituents of the gas in said sample cell, a rotary filter wheel for successively and repetitively positioning at least one filter in the path of the infrared energy, said infrared energy producing and directing means including an infrared energy source having an emissivity characteristic which varies such as to at least partially compensate for wavelength dependence of the response of lead-selenide, thermoelectrical means for maintaining the temperature of said detector means at a preselected level, means for sensing the temperature of said detector means, and bidirectional power supply means for said thermoelectric means responsive to said temperature sensing means for causing said thermoelectric means to heat or cool said detector means in relation to ambient temperature.

8. A gas analyzer comprising, a sample cell for containing gas to be analyzed, means for producing and directing infrared energy through said sample cell, detector infrared energy through said sample cell, detector means for detecting the infrared energy passing through said sample cell and producing an electrical signal representative thereof, means coupled to said detector means for processing the electrical signal to produce an output indicating the concentration of the constituents of the gas in said sample cell, a rotary filter wheel for successively and repetitively positioning at least one filter in the path of the infrared energy, means coupled to said detector means for deriving a series of synchronizing pulses related to variations in the electrical signal produced by said detector means, and servo-control means for controlling the speed of said rotary filter wheel in accordance with said synchronizing pulses.

9. A gas analyzer comprising, a sample cell for containing gas to be analyzed, means for producing and directing infrared energy through said sample cell, detector means for detecting the infrared energy passing through said sample cell and producing an electrical signal representative thereof, and means coupled to said detector means for processing the electrical signal to produce an output indicating the concentration of the constituents of the gas in said sample cell, said signal processing means including a thermistor network for compensating the output thereof for variation in the absorption characteristic of gas with temperature.