Patent Number: 039492311
Section: summary

BACKGROUND OF THE INVENTION The present invention relates generally to an infrared radiator unit, and more particularly to an infrared radiator unit for infrared analyzers. Infrared radiator units of this type are used in infrared analyzers and are electrically heated to approximately 1000K, so that the energy radiated by them is in the infrared portion of the spectrum. When such units are used in infrared analyzers for measuring purposes, specific requirements are made of them with respect, inter alia, to the direction of the infrared radiation and the constancy of the emitted radiation, as well as with respect to the energy requirements of the source. It is known that a particularly high effectiveness of the radiation utilized for measuring purposes can be obtained, if the infrared radiation which leaves the radiator unit issues in axially parallel condition, because this assures that the largest part of the radiation will enter axially parallel into the measuring or reference receptacle, rather than entering into it at an angle to impinge upon its side walls and become partly absorbed therein. To obtain this direction of the radiation it is known in the prior art to configurate the reflecting surface of the reflector of the unit as a paraboloid. However, the energy sources used in the art are not point sources but have an elongated configuration, so that a purely paraboloid-shaped reflecting surface does not adequately condense the radiation into a direct beam. Another prior-art difficulty has been the very substantial influence of heat losses via the mountings of the energy source and the unit per se, upon the constancy of the radiation intensity. The better thermal conductivity there is between the energy source, the mount for the energy source and the housing, the more substantially the temperature of the energy source will be influenced by the ambient temperature, and this in turn leads to a wavelength shift in the major portion of the emitted radiation, so that the intensity of radiation is not constant. Furthermore, it is desired that such infrared radiating units should require as little energy as possible for the operation, a condition which is particularly important if such units are employed in battery-operated infrared analyzers where the available battery energy is strictly limited. Finally, another problem that has not been solved in the art is the mechanical stability of the mounting arrangement for the radiant energy source. If the source is shifted in any way in its position relative to the optical axis of the analyzer, by mechanical vibrations or the like, then the symmetry of the arrangement is disturbed and errors in measurement can and will occur. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an improved infrared radiating unit for infrared analyzers which overcomes the disadvantages of the prior art. More particularly, it is an object of this invention to provide such an improved infrared radiating unit wherein the radiant energy is emitted largely in axial parallelism. A further object of the invention is to provide such a unit which has a constant radiation output as a result of low heat losses. In additional object of the invention is to provide such a unit which requires relatively little energy for its operation. Still a further object of the invention is to provide a unit of the type in question wherein the energy source is mounted in such a manner as to be highly stable in its position relative to the optical axis, and in which the maintenance of thermal symmetry about the optical axis of the analyzer is assured even if the device undergoes exceptionally strong vibrations or other agitation. In keeping with these objects, and with others which will become apparent hereafter, one feature of the invention resides in an infrared radiating unit for infrared analyzers which, briefly stated, comprises a cylindrically shaped source of infrared radiation, and a reflector partly surrounding the source and comprising a curved reflector section having a reflecting surface shaped to resemble an axially bisected rotationally symmetrical paraboloid, and a cylindrical reflector section extending from an open side of the curved reflector section. The focal points of the reflecting surface are located on a circle which coincides with the outer circumference of the cylindrically shaped source. The present invention is thus characterized by a combination of features which assures its unique advantages and characteristics as compared to the prior art. These characteristics involve the configuration and material of the reflector, the manner in which the reflector is mounted, and the carrier for the source of radiation. The reflector has a curved reflector portion, the reflector surface of which resembles an axially bisected rotationally symmetrical paraboloid which is pushed apart transversely of its bisection, and a cylindrical portion which extends from the curved portion of the reflector. The source of energy is a tubular coil or double coil of resistance wire having a cylindrical configuration, and the focal points of the individual cylinder-paraboloid sectors of the reflector surface are located on a circle which coincides with the circumference of this coil. The reflector itself is produced of a material having a comparatively low coefficient of thermal conductivity, preferably a rust-resistant or rust-free steel which is known to have a comparatively low coefficient of thermal conductivity. The inner surface, that is the reflective surface of the reflector, is advantageously gold plated. The contact area between the reflector and the mount for the same is small so as to reduce the thermal-wedging effect, that is to reduce thermal conduction between them. The carrier for the heating coil is of a ceramic material, and has a portion located outside the reflector and another portion which extends through an opening in the reflector into the interior thereof; this second portion has a smaller cross-sectional area than the remainder of the carrier. The latter is advantageously clamped in place, so that it can be shifted axially, can be turned about its longitudinal axis and can be replaced whenever desired or necessary. The heating coil may be mounted on a metallic sleeve, preferably of rust-free steel, having axially spaced flanges between which the heating coil is located. This sleeve can then be pushed onto the smaller cross-sectional area portion of the carrier and can be secured thereon and placed in suitable manner, for example by means of an adhesive. The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.