Method and instrument combination for producing comparability of

Details Method and instrument combination for producing comparability of Method and instrument combination for producing comparability of

1997-08-26

2000-04-11

Hannaher, Constantine

Radiant energy

Invisible radiant energy responsive electric signalling

Infrared responsive

356300, 356326, 356319, G01J 342, G01J 328

Patent

active

060490829

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a method and combination of devices for providing the comparability of spectrometer measurements, preferably in the near infrared range, with a plurality of measuring instrument individuals of the same type in a family.
NIR spectrometers have gained wide application. They are used to analyze gaseous and solid substances. With constantly increasing demands for accuracy, exact calibration of these instruments gains particular significance. It is especially important that the measured values of a specimen obtained with one spectrometer be replicable on another spectrometer of the same type.
Moreover, the accuracy of the spectral measurements is impaired by changes in the specimen being measured itself, for instance with regard to its consistency or dimensions in the case of nonhomogeneous materials. A standardizing method for reducing particle size effects is described for instance in U.S. Pat. No. 5,132,538.
It is well known to use natural (absolute) standards for standardizing the measuring instruments, among them for instance using a spectral absorption band of a gas to calibrate the wavelength scale of a spectrometer. In the field of infrared and near infrared spectroscopy, the standardization of the wavelength scale in this way is state of the art. On the other hand, the scale for the intensity is not standardized. Specimens are measured relative to a "hundred percent" standard specimen or reference. In measurements of reflection, this typically means a "hundred percent" reflector. In measurements of transmission, this typically means the signal magnitude at which there is no specimen in the beam of light. In addition, the "zero signal" can be measured by physically preventing the beam of light from reaching the detector. The signal of the specimen can then be corrected by means of the offset signal measured.
It is assumed of the signals S.sub.s and S.sub.r already corrected with the measured offset signal, it is assumed that S.sub.s /S.sub.r is directly proportional to I.sub.s /I.sub.r ; the specimen or transmitted through the specimen; or transmitted by the reference.
In fact, the design of spectrometers takes this circumstance particularly into effect by designing the detectors in such a way that they are operated in the linear range of their characteristic curve. As much as possible, the user must then make sure that I.sub.s and I.sub.r are measured under the same peripheral conditions. Many cases exist, however, in which spectrometers of the state of the art, operated in the way described above, fail in measuring an intrinsically correct signal for the reflection or transmission of a given specimen. The differences in spectral sensitivity (on the scale of intensity) between spectrometer individuals can be very great, even in those of the same family. In some cases, the sensitivity of spectrometers is directly proportional to I.sub.s /I.sub.r, but the linearity coefficients of the instruments differ from one another. In other cases, S.sub.s /S.sub.r is linked in a more-complex way to I.sub.s /I.sub.r, namely nonlinearly.
The reasons why the linearity coefficients between the instruments vary may be differences in the reflection from the reference specimen, differences in the optical adjustment, mechanical tolerances of the specimen holder, and so forth.
The reason for the nonlinear relationship between S.sub.s /S.sub.r and I.sub.s /I.sub.r may be a nonlinear detector characteristic curve, or scattered light, which depends on the reflection (transmission) of the specimen. Another reason for the nonlinearity may be multiple reflections at optical boundary layers because of great differences in the index of refraction. The nonlinear effects occur especially markedly at the point of contact with the specimen and are amplified even more if sapphire (index of refraction n=1.75) is used as window material instead of quartz (n=1.45), for instance. In many applications, however, sapphire windows are necessary, for instance because of their superior strengt

REFERENCES:
patent: 5132538 (1992-07-01), Norris

Affiliated with

Also associated with

Rating

Method and instrument combination for producing comparability of does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Method and instrument combination for producing comparability of, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and instrument combination for producing comparability of will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1178344