Furnace atmosphere measurement

A method of determining the concentration of a species in a portion of a furnace atmosphere comprising the steps:

• (i) measuring a first intensity I1 of electromagnetic radiation in the furnace at a first wavelength λ1;
• (ii) measuring a second intensity I2 of electromagnetic radiation in the furnace at a second wavelength λ2;
• (iii) measuring a third intensity I3 of electromagnetic radiation in the furnace at a third wavelength λ3, the third wavelength being selected to be representative of the absorption of electromagnetic radiation by the species;
• (iv) calculating a fourth intensity I4 at the third wavelength using the first and second intensities, the fourth intensity being an estimate of the intensity of electromagnetic radiation in the furnace at the third wavelength absent any absorbing species in the furnace atmosphere;
• and
• (v) using the third intensity and the fourth intensity to determine a parameter that is proportional to the concentration of absorbing species in the portion of the furnace atmosphere.

An apparatus for measuring the concentration of a species in a portion of a furnace atmosphere, the species absorbing electromagnetic radiation in the furnace, the apparatus comprising:

• collection means for collecting electromagnetic radiation from inside the furnace;
• coupling means for directing the collected electromagnetic radiation to a suitable measuring means, the measuring means being configured to measure the intensity of the collected electromagnetic radiation at one or more wavelengths;
• and
• computing means, in particular a computer, configured to take the output from the measuring means to determine the amount of absorption of electromagnetic radiation inside the furnace at a measurement wavelength, the measurement wavelength being selected to be representative of the absorption of electromagnetic radiation in the furnace atmosphere by the species.