NONDISPERSIVE IR ANALYZER AND METHOD FOR CALIBRATING

• US 3,562,522 A
• Filed: 09/18/1968
• Issued: 02/09/1971
• Est. Priority Date: 09/18/1968
• Status: Expired due to Term

• Current Assignee: Carl N. Cederstrand, Charles A. Keenan, James C. Davis, Jerrold H. Randall
• Original Assignee: Carl N. Cederstrand, Charles A. Keenan, James C. Davis, Jerrold H. Randall
• Inventors: Cederstrand, Carl N., Davis, James C., Keenan, Charles A., Randall, Jerrold H.
• Application Number:
  US04/760,501
• Time in Patent Office: 874 Days
• US Class Current: 250/252.1
• CPC Class Codes: F02D 41/1451 the sensor being an optical sensor
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

A nondispersive infrared analyzer having a source, flow cell, filter and detector is disclosed. The inlet to the flow cell may be switched from one of two intakes and the outlet is connected to a jet pump. With air flowing through the cell the zero suppression control is adjusted to reduce the signal input to the DC amplifier to zero. The calibration blade is started and the span control adjusted to provide a given up-scale reading of the meter. The analyzer is then calibrated to provide a reading directly in concentration of the desired constituent.

Claims

2. The analyzer of claim 1 wherein said means for introducing air and a sample to said cell comprises valve means connected to the inlet of said cell and having a pair of inlets, said valve operable to connect either of said inlets to said cell inlet.

3. The analyzer of claim 1 further comprising:

chopper means disposed in the radiation path for chopping the radiant energy;

said circuit means including amplifying and rectifying means connected to said detector to provide a DC signal of polarity and amplitude indicative of the output of said detector;

DC amplifier means connected to receive the output of said amplifying and rectifying means;

said means for adjusting said indicator to a first reading comprising signal suppression means connected to the input of said DC amplifier to reduce the input signal to zero; and

said means for adjusting said indicator to a second reading comprises a variable feedback circuit connected between the input and output of said DC amplifier means.

4. The method of calibrating an infrared analyzer having an indicator, a zero suppression circuit and a span control comprising the steps of:

introducing ambient air into the sample cell of said analyzer;

adjusting the zero suppression control to a first reading of said indicator;

chopping the radiation in the beam path of said analyzer at a frequency greater than the response time of the detector; and

adjusting the span control to a second reading of said indicator during the chopping of the radiation at said frequency.

5. The method of calibrating an infrared analyzer having a sample cell interposed in a beam path between a radiation source and a detector, an indicator, a zero suppression circuit and a span control and measuring selected constituents in the exhaust of an internal combustion engine comprising the steps of:

chopping the radiation in the beam path of said analyzer at a first frequency less than the response time of the detector at all times during the calibration and measurement;

introducing ambient air into the sample cell of said analyzer;

adjusting the zero suppression circuit to provide a first reading of said indicator;

chopping the radiation in the beam path of said analyzer at a second frequency greater than the response time of the detector;

adjusting the span control to provide a second reading of said indicator during the chopping of the radiation at said second frequency;

terminating the chopping of the radiation at said second frequency;

introducing exhaust gases from an internal combustion engine into the sample cell of said analyzer; and

providing a reading of said indicator.