Automatic gas analysis and purging system

• US 3,973,848 A
• Filed: 12/19/1974
• Issued: 08/10/1976
• Est. Priority Date: 12/19/1974
• Status: Expired due to Term

• Current Assignee: United Technologies Corporation (Rtx Corporation)
• Original Assignee: United Technologies Corporation (Rtx Corporation)
• Inventors: Cross, Thomas A., Jowett, Terence W.
• Primary Examiner(s): Corbin, John K.
• Assistant Examiner(s): Punter, Wm. H.
• Application Number:
  US05/534,525
• Time in Patent Office: 600 Days
• Field of Search: 356/51, 356/81, 356/229, 250/341, 250/343-346, 73/23
• US Class Current: 356/51
• CPC Class Codes: G01M 15/10 by monitoring exhaust gases or combustion flame
• CPC Class Codes: G01M 15/108 using optical methods
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

The contaminants in the exhaust gas emissions from a motor vehicle such as carbon monoxide (CO) and hydrocarbons (HC) are analyzed and the concentration of the contaminants together with other pertinent data is displayed in a digital manner. The exhaust gas emissions are fed into a sample cell contained within a nondispersive infrared analyzer and the absorption of an infrared radiation beam at selected wavelengths by the gas within the cell is measured. A reference cell containing a reference gas is also positioned in the infrared radiation beam path. By means of a rotating chopper disk positioned in the light path, the infrared radiation beam passes alternately through the reference cell and the sample cell and is focused at a plurality of detectors which are each sensitized to a narrow wave band by a filter and which receive the alternate sample cell and reference cell radiation pulses. Synchronization of the system is provided by a notch in the chopper disk which passes alternately between three light sources and associated photoresponsive devices. Automatic span correction is obtained by an automatic gain control circuit which maintains the reference cell output at a predetermined amplitude. The sample cell is initially filled with ambient air by a gas transport system. By measuring the sample cell and reference cell outputs with ambient air in the sample cell, and then measuring the sample cell and reference cell outputs with exhaust gas in the sample cell, a ratio can be computed which is proportional to the amount of the contaminant. Computation of the ratio in this manner results in automatic zeroing and spanning of the system. The computed ratio is then calibrated for nonlinearities in the system, and linear corrections are made for variations in ambient pressure and for variations in the temperature of the gas passing through the sample tube. Provision is also made for assuring that the vehicle being tested has achieved a predetermined engine speed and that no blockage has occurred in the gas transport system when the measurements are made. After the exhaust gas has been analyzed it is replaced in the sample cell with ambient air to prevent contamination of the system optics from the exhaust gas. A sapphire window is positioned in front of the infrared source to reduce changes in source temperature by air currents produced by the rotating chopper disk.

Claims

1. A gas analysis system for measuring the amount of a selected contaminant in a sample gas comprising:

a sample cell adapted to contain a gas;

means for generating a beam of infrared radiation;

a solenoid valve having first and second positions;

means for passing air through said solenoid valve to said sample cell when said valve is in said first position and passing said sample gas through said solenoid valve to said sample cell when said valve is in said second position;

means including a data control system for moving said valve between said first and second positions, to first purge said sample cell with air and to thereafter remove the air and fill said sample cell with the sample gas, and for passing said beam through said sample cell during the time that said cell contains air and producing a first electrical signal indicative of the absorption of said radiation by the selected contaminant in said air, and for passing said beam through said sample cell during the time that said cell contains said sample gas and producing a second electrical signal indicative of the absorption of said radiation by the selected contaminant in said sample gas, said data control system being responsive to said first and second electrical signals for producing an output signal indicative of the amount of said selected contaminant in said sample gas and purging said sample cell with air immediately after generation of said output signal by moving said valve from said first position to said second position in response to generation of said output signal.