Digital anesthetic agent analyzer

• US 4,692,621 A
• Filed: 10/11/1985
• Issued: 09/08/1987
• Est. Priority Date: 10/11/1985
• Status: Expired due to Term

• Current Assignee: Anros Analyzers Incorporated, AC Limited (Emirate of Dubai (United Arab Emirates))
• Original Assignee: Andros Anlayzers Incorporated
• Inventors: Williams, Kevin G., Parnoff, George K., Rogers, Raymond E., Passaro, Robert E.
• Primary Examiner(s): Howell, Janice A.
• Assistant Examiner(s): Hannaher, Constantine
• Application Number:
  US06/786,736
• Time in Patent Office: 697 Days
• Field of Search: 250/351, 250/339, 250/343, 250/252.1, 356/439, 356/438, 356/437
• US Class Current: 250/343
• CPC Class Codes: G01N 2021/3129 Determining multicomponents by multiwavelength light
• CPC Class Codes: G01N 21/314 with comparison of measurements at specific and non-specific wavelengths dual wavelength spectrometry G01J3/427
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01N 2201/127 Calibration; base line adjustment; drift compensation
• CPC Class Codes: G01N 2201/12723 Self check capacity; automatic, periodic step of checking

Abstract

A gas analyzer is described comprising a sample cell for containing a gas mixture to be analyzed, a source for producing and directing infrared energy through the sample cell, a rotary filter wheel having at least one filter thereon for passing infrared energy limited to a wavelength band within the characteristic absorption band of a predetermined gas and having a dark level region substantially opaque to infrared energy, a drive for supporting and rotating the filter wheel to successively interpose the filter and the dark level region between the source and the sample cell in the path of the infrared energy directed by the source, a detector for detecting infrared energy passing through the sample cell and producing an electrical signal representative thereof, and a signal processor connected to the detector for producing an output indicating the concentration of the predetermined gas in the sample cell by comparing the electrical signals produced by the detector with the filter positioned in the infrared energy path and with the dark level region positioned in the infrared energy path. The dark level region has a substantially fully reflective surface oriented toward the sample cell when positioned in the infrared energy path whereby infrared energy impinging thereon is reflected.

Claims

1. A gas analyzer comprising, a sample cell for containing a gas mixture to be analyzed, source means for producing and directing infrared energy through said sample cell, a rotary filter wheel having at least one filter thereon for passing infrared energy limited to a wavelength band within the characteristic absorption band of a predetermined gas and having a dark level region substantially opaque to infrared energy, drive means for supporting and rotating said filter wheel to successively interpose said filter and said dark level region between said source means and said sample cell in the path of the infrared energy directed by said source means, detector means for detecting infrared energy passing through said sample cell and producing an electrical signal representative thereof, signal processing means connected to said detector means for producing an output indicating the concentration of the predetermined gas in the sample cell by comparing the electrical signals produced by said detector means with said filter positioned in the infrared energy path and with said dark level regions positioned in the infrared energy path, said filter wheel including a second filter for passing first and second infrared wavelength bands, one of which is within a region of infrared absorption by water vapor and the other of which is not, both of said first and second wavelength bands of said second filter being outside the characteristic wavelength absorption regions of other gases present in the sample cell, the amplitude of transparency of said second filter at each of said first and second infrared wavelength bands being selected to track the variation in absorption of infrared energy at the wavelength of said first filter due to the presence of water vapor in said sample cell.

2. A gas analyzer according to claim 1 wherein said dark level region has a substantially fully reflective surface oriented toward said sample cell when positioned in the infrared energy path such that infrared energy impinging thereon is reflected and wherein said reflective surface of said dark level region is positioned in substantially the same place of rotation as the side of said filter facing said sample cell.

3. A gas analyzer according to claim 1 wherein the interior surfaces of said sample cell are comprised substantially of a material having a low affinity for, bonding with water molecules.

4. A gas analyzer according to claim 3 wherein said material is selected from the group consisting of silicon oxide, magnesium fluoride and gold.

5. A gas analyzer according to claim 1 including means for sensing the ambient temperature and for activating said automatic zeroing means upon a change in ambient temperature said source of a predetermined amount.

6. A gas analyzer according to claim 1 including a reference filter in said filter wheel, said signal processing means including means for comparing the level of infrared energy passing through said sample cell when said filter is interposed in the path of infrared energy and when said reference filter is interposed in the path of the infrared energy, means for monitoring the amplitude of the signal detected by said detector means with said reference filter interposed in the path of infrared energy and for activating said automatic zeroing means upon a change in the level of said signal of a predetermined amount.