Patent ID: 8665424

Claim:
An optical absorption gas analyser for determining the concentration of a target gas in a sample, comprising: a chamber for containing the sample in use; an optopair, comprising a light emitting diode (LED) arranged to emit radiation into the chamber and a photovoltaic radiation detector arranged to detect radiation transmitted through the chamber from the LED and to output a corresponding detection signal S S ; a temperature sensor arranged in thermal contact with the LED and the photovoltaic radiation detector, and to output a temperature signal T representing the temperature of the optopair; a memory having stored therein data representative of the baseline detection signal S T output by the optopair in the absence of the target gas as a function of the temperature of the optopair across a range of temperatures, the memory further storing processor-executable instructions for causing the processor to: record the detection signal S S output by the optopair against the temperature signal T in the memory as the optopair is subjected to a change in temperature, to thereby provide and store the data representative of the baseline detection signal S T in the memory; generate a differential detection signal S A indicative of the concentration of target gas in the sample by retrieving from the memory the baseline detection signal S T corresponding to the temperature signal T; and calculate the difference between the detection signal S S and the baseline detection signal S T ; and a processor for executing the processor-executable instructions to: record the detection signal S S output by the optopair against the temperature signal T in the memory as the optopair is subjected to a change in temperature, to thereby provide and store the data representative of the baseline detection signal S T in the memory; generate a differential detection signal S A indicative of the concentration of target gas in the sample by retrieving from the memory the baseline detection signal S T corresponding to the temperature signal T; and calculate the difference between the detection signal S S and the baseline detection signal S T .