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Correction for Media Absorption of Transmitted Light Intensity in Optical Pyrometry

IP.com Disclosure Number: IPCOM000122324D
Original Publication Date: 1991-Nov-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 1 page(s) / 41K

Publishing Venue

IBM

Related People

Chang, J: AUTHOR [+3]

Abstract

A correction factor for an absorbing transmission medium is determined and applied to temperature found through a second order polynomial function of intensity. Where it is feasible, an alternative is to measure intensity of a portion of the transmitted spectrum in which the light transmission medium is not absorptive.

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Correction for Media Absorption of Transmitted Light Intensity in
Optical Pyrometry

      A correction factor for an absorbing transmission medium is
determined and applied to temperature found through a second order
polynomial function of intensity.  Where it is feasible, an
alternative is to measure intensity of a portion of the transmitted
spectrum in which the light transmission medium is not absorptive.

      Optical pyrometry is used to measure temperature of objects
contained in various ambient gases for a variety of processes, e.g.,
in rapid thermal annealing (RTA). Intensity of transmitted light in a
wavelength band in the near infrared is measured and translated to
temperature by a second order polynomial fit of temperature (T) as a
function of intensity (I), i.e.:
      T = AI2 + BI + C,
where A, B, and C are known fitting coefficients for a given
pyrometer.

      A correction for intensity (dT) due to absorption of intensity
of transmitted light by an ambient gas is found by creating
calibration curves of change of intensity (dI) versus optical
wavelength and using:
      dT = (2AI + B)dI,
where dI is taken at the appropriate wavelength.

      Where there is a wavelength of transmitted light that is
proportional to temperature change and not absorbed by the
transmitting medium, it is feasible to used narrow bandpass filters
to avoid the necessity of applying a correction factor.

      Disclosed anonymously.