Device for measuring scattered light from a measurement volume with compensation for background signals

Abstract

A device for measuring scattered light from a measurement volume with compensation for background signals, includes a light sensor having separately evaluable light-sensitive elements, a single imaging optical system, wherein the light-sensitive elements are arranged in the image plane and the measurement volume is arranged in the corresponding object plane of the optical system, a light transmitter with a collimated light beam, this light-sensitive element detects scattered light from the measurement volume and background light from the overlapping visual ranges behind the subject plane, and the other light-sensitive element detects no or significantly less scattered light from the measurement volume and background light from the overlapping visual areas behind the object plane, and a diaphragm that restricts the visual ranges of the light-sensitive elements behind the object plane.

Claims

1. A device for measuring scattered light from a measurement volume with compensation for background signals, comprising at least one light sensor having at least two separately evaluable light-sensitive elements, a single imaging optical system, wherein the light-sensitive elements are arranged in the image plane and the measurement volume is arranged in the corresponding object plane of the optical system, the visual ranges of the light-sensitive elements are completely separate from each other in the object plane and overlap each other behind the object plane, a light transmitter with a collimated light beam, which only passes through, or at least primarily passes through, the visual range of the one light-sensitive element within an area extending through the object plane and bordering the measured volume such that this light-sensitive element detects scattered light from the measurement volume and background light from the overlapping visual ranges behind the subject plane, and the other light-sensitive element detects no or significantly less scattered light from the measurement volume and background light from the overlapping visual areas behind the object plane, and a diaphragm that is arranged between the optical system and the light-sensitive elements that restricts the visual ranges of the light-sensitive elements behind the object plane such that the areas of the two visual ranges which do not overlap each other are partially or completely hidden.

2. The device according to claim 1, wherein the light transmitter is aligned such that the light beam only passes through the visual range of the one light-sensitive element.

3. The device according to claim 1, wherein the diaphragm restricts the visual range of the light-sensitive elements to the overlapping area of the two visual ranges such that the two light-sensitive elements detect background light to the same degree.

4. The device according to claim 1, further including an evaluation device that is connected to the at least one light sensor and that detects the amount of the measurement signals supplied from the light-sensitive elements that originates from the measured volume, wherein the evaluation device compensates for the amount originating from the background light.

5. The device according to claim 1, wherein the diaphragm is arranged in the image plane of a background wall.

6. The device according to claim 1, wherein the diaphragm is arranged in the image side focal point of the optical system.

7. The device according to claim 1, wherein the diaphragm has an aperture that has at most the value calculated according to the following formula: $h_{\mathrm{Blende}}=-h_{\mathrm{Det}}+\frac{B_{\mathrm{MV}}-B_{\mathrm{HG}}}{B_{\mathrm{MV}}}\left(\frac{A}{2}+h_{\mathrm{Det}}\right)$ wherein the following holds true: h.sub.Blende/Diaphragm=maximum height or half aperture of the diaphragm h.sub.Det=height or half diameter of the detector B.sub.MV=image distance of the measurement volume B.sub.BW=image distance of the background wall A=Diameter of the imaging system.

8. The device according to claim 1, further including a diaphragm with an adjustable aperture or means for displacing the diaphragm toward the optical axis of the optical system.

9. The device according to claim 1, wherein the optical system comprises a lens or concave mirror.

10. The device according to claim 1, wherein the light transmitter comprises a laser or LED.

11. The device according to claim 1, wherein the light-sensitive elements are formed in a single light sensor.

12. The device according to claim 1, wherein the light-sensitive elements are formed in different light sensors.

13. The device according to claim 1, wherein the light transmitter is aligned at a sharp angle relative to the optical axis of the imaging optical system.

14. The device according to claim 13, wherein the light transmitter or the light beam is arranged on the side next to the optical system.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The present invention will be explained in more detail in the following by way of the attached drawings. In the drawings show:

(2) FIG. 1 a conventional device in a roughly schematic side view;

(3) FIG. 2 a device according to the present invention with diaphragm in the image plane of a background wall, in a roughly schematic side view;

(4) FIG. 3 a device according to the present invention with diaphragm in the image side focal point of the imaging optical system in a roughly schematic side view;

(5) FIG. 4 a device according to the present invention with a concave mirror as imaging optical system in a roughly schematic partial side view; and

(6) FIG. 5 the arrangement of the light transmitter and the path of the light beam in the measurement device in a roughly schematic perspective view.

DETAILED DESCRIPTION OF THE INVENTION

(7) In the following explanation of different realisation examples, coincident or essentially coincident components and details of the light path are provided with coincident reference numerals.

(8) While this invention may be embodied in many different forms, there are described in detail herein a specific preferred embodiment of the invention. This description is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiment illustrated.

(9) According to FIG. 1, a light sensor 1 has two or more separately evaluable light-sensitive elements 1a, 1b. The segmented light sensor 1 is situated in the image plane of an imaging system 2 in the form of a biconvex lens. The measurement volume is in the corresponding object plane.

(10) Whereas the visual ranges 3a, 3b of the light-sensitive elements 1a, 1b are completely separate from each other in the object plane, the visual ranges overlap each other outside of object plane. The visual ranges 5a, 5b overlap each other on a background wall 4. As a result, the light-sensitive elements 1a, 1b measure a similar, but not the same background radiation.

(11) According to FIG. 2, a harmonisation of the visual ranges 5a, 5b on the background wall 4 is achieved by a diaphragm 6, which is arranged in the image plane of the background wall. Through this arrangement of the diaphragm 6, the ranges 5a, 5b imaged in the background overlap exactly.

(12) FIG. 3 shows a special case, where the background wall 4 is assumed in the optically seen infinite. In this case, the diaphragm 6 is placed in the image side focal point of the lens 2, and the beams, which define the image on the wall, run in parallel.

(13) In the realisations of FIGS. 2 and 3, the imaging optical system may consist of one lens 2 as well as of plural lenses.

(14) In the realisation of FIG. 4, the imaging optical system is realised as a concave mirror 2. In this realisation, the light sensor 1 with the light-sensitive elements 1a, 1b is situated between the concave mirror 2 and the measurement volume, and the diaphragm 6 is situated between the light sensor 1 and the concave mirror 2. In this example, the diaphragm 6 is placed in the image plane of the background wall. For the rest, the light path is according to FIG. 2 in this realisation. The symmetry axis of the concave mirror is advantageously in a small angle to the optical axis of the system, so that the diaphragm 6 and the elements 1a, 1b do not shadow the incident light with respect to the concave mirror 2. Thus, the elements 1a, 1b are arranged before or respectively behind the plane of projection of FIG. 4.

(15) According to FIG. 5, a collimated light transmitter 7 emits a light beam 8 from a position laterally next to the imaging optical system 2 in a sharp angle to the optical axis of the imaging optical system 2 such that the same passes in the image plane only through the range 3b which the one light-sensitive element 1b looks up. On the contrary, the light beam 8 does not pass through the range 3a, which is looked up by the other light-sensitive element 1a. Before and behind the object plane, the light beam passes only through the visual range of the one light-sensitive element 1b. The complete range in which the light beam 8 passes through the visual range of the one light-sensitive element lb limits the measurement volume.

(16) According to FIG. 2, an evaluation device 9 is connected to the light sensor 1, which determines the measurement signal originating of scattered light from the signals provided by the light-sensitive elements 1a, 1b by compensating the background signal.

(17) This completes the description of the preferred and alternate embodiments of the invention. Those skilled in the art may recognize other equivalents to the specific embodiment described herein which equivalents are intended to be encompassed by the claims attached hereto.