a) Field of the Invention
The present invention is directed to an arrangement and accompanying method for compensation of the temperature dependency of detectors in spectrometers. An increased measuring accuracy can be ensured in a broad range of application temperatures by the improved stabilization of the detector temperature.
b) Description of the Related Art
Spectrometers are used in process measurement engineering to determine the concentration or layer thickness of chemical substances. These chemical substances are detected or quantitatively determined on the basis of known or previously measured characteristic spectra.
The sensitivity of the detectors is highly dependent upon temperature, which is an obstacle to broad application. The temperature dependency increases sharply particularly at the long-wave end of the detection range. This is especially critical when the characteristic spectrum of the substance to be determined lies exactly at this long-wave end of the detection range. Therefore, the effort is made to keep the temperature of the detectors constant as far as possible. In order to determine exact measurement values, the stabilization must sometimes be carried out to a fraction of a Kelvin. This can only be realized at great expense because the ambient temperature, which sometimes fluctuates considerably, also has an additional influence on the detectors.
The Utility Model Application DE 200 08 622 U1 describes a sensor device for optical spectroscopy, for example, which enables an online process control. The measurement of the samples is carried out by means of an immersion probe whose optical characteristics are likewise highly dependent upon the temperature of the substance to be examined. When measuring samples at different temperatures, the probe must be kept in the sample for a longer period of time for temperature compensation in order to prevent measurement errors. In order to be able to determine the point in time for temperature compensation, the sensor device has a temperature gauge which makes it possible to carry out a measurement only when temperature compensation has been carried out. While this arrangement ensures that only correct measurements are determined, all-purpose use is impossible due to the lack of temperature compensation.
Further, solutions are known from the prior art in which the temperature of the detector is maintained constant. Detectors of this kind which have a temperature gauge are offered, for example, by HAMAMATSU (data sheet: “Image Sensors—InGaAs linear image sensor G9211 to 9214/9205 to 9208 series”, http://www.hamamatsu.com).
In contrast, temperature regulating units with a corresponding control unit are offered by other manufacturers such as HYTEC Microsystems (data sheet: “Subminiature Controller for Thermoelectric Coolers—HY5605”, http://www.hytek.com).
Since the temperature gauge is always arranged at a finite distance from the detector rather than on the detector, the exact detector temperature can never be determined.
Solutions of the type mentioned above have the disadvantage that the temperature gauge for the regulating circuit can only be mounted at a finite distance from the detector. Therefore, an absolutely accurate temperature control is never possible. Mass applications cannot be carried out because it is too costly to stabilize the temperature of the detector. On the other hand, the required measuring accuracy cannot be ensured in the application temperature range without stabilizing the temperature of the detector surface.