Method for remotely measuring temperatures which utilizes a two wavelength radiometer and a computer

A method for measuring the temperature of tubes disposed within a furnace having heated walls which are maintained at a relatively high temperature, the tubes being spaced from the walls and having surfaces which are heated to relatively low temperature by radiation from the walls, said surfaces in turn emitting radiation at said relatively low temperature, said method employing a two wavelength radiometer and a computer, said method comprising the steps of:

• selecting first and second wavelengths, the second wavelength being shorter than the first wavelength, both walls and tubes exhibiting appreciable radiation at the first wavelength, the walls emitting appreciable radiation while the tubes emit essentially no radiation at the second wavelength;
• measuring with the radiometer the radiation of said walls at the first wavelength and at the second wavelength and storing these two walls radiation measurements in the computer;
• measuring with the radiometer the radiation of said tubes at the first wavelength and at the second wavelength and storing these two tubes radiation measurements in the computer;
• and
• using the two stored tubes radiation measurements and the two stored walls radiation measurements in the computer to calculate the temperature of the tubes.