Patent ID: 8073637

Claim:
An apparatus comprising: a first sensor producing a first data signal characterizing a carbon dioxide concentration in the gas stream, the first sensor comprising a tunable diode laser absorption spectrometer comprising a laser light source that is modulated at a modulation frequency while being scanned over a wavelength range that includes a selected absorption transition for carbon dioxide and a detector that detects an intensity of light reaching the detector at a multiple of the modulation frequency after light from the laser light source passes through the gas stream, the first data signal comprising the intensity as a function of wavelength at the multiple of the modulation frequency; and a master processor that receives the first data signal and measurements of pressure and temperature in the gas stream, the master processor performing operations comprising: demodulating the intensity as a function of wavelength at the multiple of the modulation frequency received in the first data signal to remove a sloping baseline caused by the scanning of the laser light source over the wavelength range and to calculate the carbon dioxide concentration in the gas stream based on a signal strength of the demodulated intensity at the selected absorption transitions; calculating a total nitrogen and inert species concentration in the gas stream as a remainder when the calculated carbon dioxide concentration and an inferred total hydrocarbon concentration are subtracted from 100%, the inferred total hydrocarbon concentration in the gas stream being based on a database of characteristic natural gas concentrations; and implementing an algorithm that determines an energy content of the gas stream using as inputs the measured temperature, the measured pressure, the carbon dioxide concentration, and the calculated total nitrogen and inert species concentration.