Non-dispersive infrared gas analyzer
First Claim
1. A non-dispersive infrared gas analyzer, comprising, a sample cell for containing the gas mixture to be analyzed, means for directing infrared energy through said sample cell, means for periodically interrupting the infrared energy at a predetermined frequency, detector means responsive to the infrared energy at at least one preselected wavelength to produce an AC signal having an amplitude proportional to the infrared energy passing through said sample cell and having a frequency corresponding to the predetermined frequency, said preselected wavelength corresponding to the characteristic absorption wavelength of a preselected gas, and signal processing means for processing the AC signal output of said detector means to produce a DC signal having an amplitude proportional to the concentration of the preselected gas in the mixture being analyzed, said signal processing means including an output amplifier and first variable control means manually adjustable to adjust the gain of said output amplifier to bring the output of said output amplifier to zero with a non-absorbing gas in said sample cell, and second variable control means connected in a feedback loop to said output amplifier for span calibration.
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Abstract
A non-dispersive infrared gas analyzer is described. Infrared energy is directed through a sample cell, and is interrupted at a predetermined frequency. The infrared energy at at least one preselected wavelength is detected to produce an AC signal having an amplitude proportional to the infrared energy passing through said sample cell and having a frequency corresponding to the predetermined frequency. The preselected wavelength corresponds to the characteristic absorption wavelength of a preselected gas. This AC signal is processed to produce a DC signal having an amplitude proportional to the concentration of the preselected gas in the mixture being analyzed. The signal processor includes an output amplifier, a voltage biasing network including a summing junction connected to the input of the amplifier, and a first variable control manually adjustable to bring the current at the summing junction to zero in the presence of a non-absorbing gas in the sample cell. A second variable control is connected in a feedback loop from the output of the amplifier to the input thereof for span calibration.
56 Citations
11 Claims
- 1. A non-dispersive infrared gas analyzer, comprising, a sample cell for containing the gas mixture to be analyzed, means for directing infrared energy through said sample cell, means for periodically interrupting the infrared energy at a predetermined frequency, detector means responsive to the infrared energy at at least one preselected wavelength to produce an AC signal having an amplitude proportional to the infrared energy passing through said sample cell and having a frequency corresponding to the predetermined frequency, said preselected wavelength corresponding to the characteristic absorption wavelength of a preselected gas, and signal processing means for processing the AC signal output of said detector means to produce a DC signal having an amplitude proportional to the concentration of the preselected gas in the mixture being analyzed, said signal processing means including an output amplifier and first variable control means manually adjustable to adjust the gain of said output amplifier to bring the output of said output amplifier to zero with a non-absorbing gas in said sample cell, and second variable control means connected in a feedback loop to said output amplifier for span calibration.
- 9. A non-dispersive infrared gas analyzer, comprising, a sample cell for containing the gas mixture to be analyzed, means for directing infrared energy through said sample cell, means for periodically interrupting the infrared energy at a predetermined frequency, detector means responsive to the infrared energy at at least one preselected wavelength to produce an AC signal having an amplitude proportional to the infrared energy passing through said sample cell and having a frequency corresponding to the predetermined frequency, said preselected wavelength corresponding to the characteristic absorption wavelength of a preselected gas, and signal processing means for processing the AC signal output of said detector means to produce a DC signal having an amplitude proportional to the concentration of the preselected gas in the mixture being analyzed, said signal processing means including an output amplifier, a voltage biasing network including a summing junction connected to the input of said output amplifier, first variable control means manually adjustable to bring the voltage at said summing junction to zero in the presence of a non-absorbing gas in said sample cell, and second variable control means connected in a feedback loop from the output of said output amplifier to the input thereof for span calibration.
Specification