Radiant energy – Calibration or standardization methods
Patent
1995-01-17
1997-02-18
Fields, Carolyn E.
Radiant energy
Calibration or standardization methods
250332, G01J 506, G01J 552
Patent
active
056043465
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an arrangement for recording an IR-image of an object.
DESCRIPTION OF THE RELATED ART
Hitherto, IR-cameras have been constructed with optical scanning systems provided with rotating and/or oscillating scanning components. These systems scan an object and direct the beam path onto only a few detectors which are responsive to infrared light, these detectors producing a varying video signal which can be recorded on a TV-type screen. In recent times, however, a new technique has been introduced in which image scanning is effected with a focal plane array of detectors placed in an image plane, instead of using movable components. According to this new technique, each pixel itself creates an individual detector element. Although this technique was initially expensive, it has now begun to reach reasonable price levels. Neither is the technique completely novel, since a number of FPA-systems are available, although it is primarily the different detector materials which distinguish from one another. For instance, the detector elements may be pyroelectrical, Schottky Ptsi, InSb, MCT, PbSe, GaAs, etc. This type of technique is used particularly in military systems.
That which primarily distinguishes IR-cameras for civilian use, particularly those cameras retailed by Applicant's AGEMA INFRARED SYSTEMS AB, from at least the majority of military systems, is that the military systems solely show a picture of the temperature distribution of scanned objects, whereas IR-cameras for civilian use also measure the temperature at all pixels or picture elements.
Consequently, an IR-camera intended for civilian use will have higher demands on absolute temperature accuracy than the military systems. Accordingly, the IR-camera has incorporated temperature references which are moved automatically into the beam path of the detector or the detector elements at least once with each image and the IR-camera is self-calibrating in accordance with these references.
The FPA-systems hitherto presented commercially include no actual temperature references, and neither can they measure temperature particularly well. On the other hand, the FPA-systems often include a disc of uniform temperature which can be brought into the beam path, often automatically at given time points, so as to enable all of the detector elements to be calibrated to deliver the same output signal when they look at object points that have the same temperature. Variants of the FPA-system are also found in which it is possible to look with the entire camera onto an external, heated disc, so as to enable the amplification from each individual detector element, i.e. each pixel, to be calibrated.
However, the intention with the aforesaid temperature adjusting arrangements of FPA-systems is solely to ensure that the best possible picture or image is obtained, which is fulfilled when all detector elements deliver an equally large output signal for an equally large radiation signal. This intention has nothing whatsoever to do with measuring temperature.
SUMMARY AND OBJECTIONS OF THE INVENTION
The main object of the invention is to provide an which has temperature measuring properties.
Another object of the invention is to render all of the detector element output signals independent of detector temperature, long-term operation, the intrinsic temperature of the camera (background radiation), the temperature of a disc inserted into the beam path at given time points, etc.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in more detail with reference to the accompanying drawings, in which
FIG. 1 illustrates schematically an optical array with a given beam path of a first embodiment of the inventive arrangement;
FIG. 2 illustrates schematically an exemplifying embodiment of a temperature reference arrangement with associated optics in accordance with the invention; and
FIG. 3 illustrates a third exemplifying embodiment of the inventive temperature reference arrangemen
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Guldevall Ulf
Hamrelius Torbjorn
Agema Infrared Systems AB
Fields Carolyn E.
Glick Edward J.
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