Detector Tube

The present invention pertains to a detector tube having the features of a rodshaped reagent carrier placed into a transparent tube, where the reagent carrier is provided with a detection substance.

A detector tube of this type has become known from DE Patent No. 932750. Sticks of a porous sintered material, which are impregnated with the detection reagent, are used as reagent carriers in the prior-art detector tube. The sticks are placed into the tubular glass body of the detector tube such that they are located in the direction of the longitudinal axis of the detector tube. A core, around which the sticks are arranged, is provided within the detector tube to fix the sticks within the detector tube.

The drawback of the prior-art detector tube is that a plurality of sticks impregnated with detection reagent must be introduced into the glass body, and that it is difficult to establish homogeneous flow conditions within the detector tube because of the number of sticks.

The basic object of the present invention is to improve a reagent carrier for a detector tube such that it can be placed into the detector tube in a simple manner and that defined flow conditions become established around the reagent carrier.

This object is accomplished by forming the cross-sectional contour of the reagent carrier as a polygon in such a way that at least some of the outer edges of the reagent carrier are in contact with an inner side of the tube.

The advantage of the present invention is essentially that simple and inexpensive manufacture of the detector tube is made possible by the use of a single reagent carrier with a cross-sectional contour that is dimensioned such that some of the outer edges or all outer edges are in contact with the inner wall of the glass body. Flow channels, through which the gas to be tested flows, are formed between the reagent carrier and the glass body. Especially favorable are uniform cross-sectional contours of the detector tube, in which approximately equal air resistances, which lead to a homogeneous flow through the detector tube, become established in the flow channels. The flow resistance can be adapted to prior-art detector tubes, which are filled with a granular reagent, by selecting the number of flow channels or their flow cross sections.

Star-shaped cross-sectional contours are especially advantageous for the reagent carrier. Preferred cross-sectional contours for the reagent carrier also include an equilateral triangle, a square, or an equilateral pentagon or hexagon.

The detection reagent is preferably applied as a coating to the reagent carrier. Dip-coating, spin coating, the ink jet process or sol-gel processes, as they are known from DE 4303860 A1, are especially suitable coating processes. An especially uniform distribution of the reagent on the reagent carrier is achieved with such coating processes.

The materials suitable for the reagent carrier are glass, ceramic or plastics, e.g., perfluoroethylenepropylene (FEP).

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.

In the drawings:

FIG. 1 is a view of the longitudinal section of a detector tube with a reagent carrier

FIG. 2 is a sectional view of the detector tube according to FIG. 1 along the intersecting line II--II; and

FIG. 3 is a sectional view of the detector tube according to FIG. 1 along the intersecting line III--III with reagent carriers of different designs.

Referring to the drawings, especially FIG. 1, the detector tube 1 and a reagent carrier 2 is held within a glass body 4 by means of individual beads or protrusions 3. The reagent carrier 2 consists of perfluoroethylenepropylene (FEP) and is provided with a reagent layer 5, which was applied according to the ink jet process known from DE 43 03 860 A1. The reagent layer 5 is shown as a dot matrix in FIG. 1.

FIG. 2 shows a sectional view of the detector tube 1 according to FIG. 1 in the area of the beads 3 along the intersecting line II--II. The beads or protrusions 3 touch the reagent carrier 2 at points only in three areas, so that a free flow cross section is still left between the glass tube 4 and the reagent carrier 2.

FIG. 3 shows sectional view III--III from FIG. 1 of different designs of reagent carriers of the detector tube 1 according to FIG. 1. Identical components are designated by the same reference numbers as in FIG. 1. Preferred cross-sectional contours of the reagent carrier are an equilateral triangle 21, a square 22, a regular pentagon 23, a hexagon 24, or star-shaped cross sections 25, 26, 27. The reagent carriers 21, 22, 23, 24, 25, 26, and 27 are designed such that their outer edges 6 are in contact with the inner side 7 of the glass tube 4. Only the outer edges 6 of the reagent carrier 21 are provided with reference numbers for the sake of greater clarity. Flow channels 8, through which the air to be tested can reach the reagent layer 5, are formed between the reagent carriers 2, 21, 22, 23, 24, 25, 26, 27 and the glass tube 4. The flow resistance of the detector tube 1 can be changed by valying the cross-sectional contour of the reagent carrier. Thus, detector tubes 1 with the reagent carriers 21, 22, 25, 26, and 27 have a relatively low flow resistance, while it is higher in the case of the reagent carriers 23 and 24.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.