Automatic gain control for an infrared source of an automotive emissions analyzer
First Claim
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1. An automatic gain control for driving a radiant energy source and controlling a constant energy emission for an automotive emission measurement system having a chopper means for chopping radiant energy passing from the source through a gas to be measured and onto a radiant energy detector, comprising:
- a gain control filter for passing chopped radiant energy of preselected wavelengths;
radiant energy detector means positioned for receiving radiant energy passed by said control filter, said detector means generating a detector signal oscillating according to the chopping of the chopper means;
detector temperature controlling means for maintaining a temperature stable detector signal output of said radiant energy detector means, said detector temperature controlling means including detector temperature measuring means for monitoring the relative temperature of said radiant energy detector means;
demodulation means for demodulating said detector signal and generating a demodulated D.C. signal;
comparator means for comparing said demodulated D.C. signal with respect to a reference signal level for generating an error signal; and
means responsive to the amplitude of said error signal for driving said infrared source.
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Abstract
An automatic gain control circuit for driving a low mass infrared source used in an automotive exhaust gas emissions analyzer. A reference spectrum of radiant energy is monitored, demodulated and converted to an error signal to maintain the source at a constant energy output.
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Citations
13 Claims
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1. An automatic gain control for driving a radiant energy source and controlling a constant energy emission for an automotive emission measurement system having a chopper means for chopping radiant energy passing from the source through a gas to be measured and onto a radiant energy detector, comprising:
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a gain control filter for passing chopped radiant energy of preselected wavelengths; radiant energy detector means positioned for receiving radiant energy passed by said control filter, said detector means generating a detector signal oscillating according to the chopping of the chopper means; detector temperature controlling means for maintaining a temperature stable detector signal output of said radiant energy detector means, said detector temperature controlling means including detector temperature measuring means for monitoring the relative temperature of said radiant energy detector means; demodulation means for demodulating said detector signal and generating a demodulated D.C. signal; comparator means for comparing said demodulated D.C. signal with respect to a reference signal level for generating an error signal; and means responsive to the amplitude of said error signal for driving said infrared source. - View Dependent Claims (3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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2. An automatic gain control for driving a radiant energy source and controlling a constant energy emission for an automotive emission measurement system having a chopper means for chopping radiant energy passing from the source through a gas to be measured and onto a radiant energy detector, comprising:
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a gain control filter for passing chopped radiant energy of preselected wavelengths; radiant energy detector means positioned for receiving radiant energy passed by said control filter, said detector means generating a detector signal oscillating according to the chopping of the chopper means; demodulation means for demodulating said detector signal and generating a demodulated D.C. signal; comparator means for comparing said demodulated D.C. signal with respect to a reference signal level for generating an error signal; and means responsive to the amplitude of said error signal for driving said infrared source.
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Specification