Patent ID: 6414310
Filing Date: 2002-07-02
Classification: G01J,G01N

Abstract:
An apparatus for measuring the concentration of a target gas using an infrared detector wherein the detector has a first output voltage representative of a first infrared wavelength absorbed by the target gas concentration, and has a second reference output voltage representative of a second infrared wavelength not absorbed by the target gas concentration, comprising:a) a BALANCE circuit connected to receive the first output voltage, said BALANCE circuit having a digitally controlled input potentiometer circuit having an addressable dual digital potentiometer which is separately addressable over control signal lines, whereby the input potentiometer circuit is initially set to provide a BALANCE circuit output voltage indicative of zero target gas concentration; b) a two-position switch connected to said second reference output voltage and to said BALANCE circuit output, said switch being selectable to connect either of said second reference output voltage or said BALANCE circuit output to a switch output terminal; c) an AGC circuit connected to said switch output terminal, said AGC circuit having a digitally controlled input potentiometer circuit, said input potentiometer circuit having an addressable dual digital potentiometer which is separately addressable over control signal lines, being periodically adjusted to provide an AGC output circuit voltage equal to said second reference output voltage; d) a SPAN circuit connected to said AGC output voltage, said SPAN circuit having a digitally controlled input potentiometer circuit comprising an input circuit having an addressable dual digital potentiometer which is separately addressable over control signal lines, and having a SPAN output terminal and said digitally controlled input potentiometer circuit being adjustable to provide a SPAN output voltage at said SPAN output terminal; and e) a computer processor connected to receive said SPAN output voltage, and having means for converting said SPAN output voltage to a digital value, said computer processor further having said control signal lines connected to said AGC circuit digitally controlled input potentiometer circuit, said SPAN circuit digitally controlled input potentiometer circuit, and said BALANCE circuit digitally controlled input potentiometer circuit, said computer processor further having means for generating control signals over said control lines in response to said SPAN output voltage, said control signals further control in said switch position, said AGC circuit output voltage, said BALANCE circuit output voltage, and said SPAN output voltage.