DEVICE FOR THE SCATTERED LIGHT MEASUREMENT OF PARTICLES IN A GAS

Abstract

A device for scattered light measurement of particles in a gas, comprising a light source, a beam splitter which splits a light beam emitted by the light source into a measuring beam and a reference beam, a light receiving device arranged at a distance from the beam splitter, which comprises at least one lens arranged in the reference beam with an optical axis aligned at an acute angle to the measuring beam, a first light receiver on the side of the lens facing away from the beam splitter, for receiving the scattered light imaged by the latter from a measurement volume in a gas-bearing region between the beam splitter and the lens, and a second light receiver on the side of the lens facing away from the beam splitter for receiving the reference beam imaged by the latter.

Claims

1. A device for scattered light measurement of particles in a gas comprising a light source (1), a beam splitter (3) which splits a light beam (2) emitted by the light source (1) into a measuring beam (2.1) and a reference beam (10), a light receiving device (13) arranged at a distance from the beam splitter (3), which light receiving device (13) comprises at least one lens (7) arranged in the reference beam (10) with an optical axis aligned at an acute angle to the measuring beam, a first light receiver (8) on the side of the lens (7) facing away from the beam splitter (3) for receiving the scattered light imaged by the latter from a measurement volume (5.1) in a gas-bearing region between the beam splitter (3) and the lens (7), and a second light receiver (12) on the side of the lens (7) facing away from the beam splitter (3) for receiving the reference beam (10) imaged by the latter.

2. The device according to claim 1, wherein the beam splitter (3) is a prism.

3. The device according to claim 1, wherein a light attenuating element (11) is arranged in the reference beam (10).

4. The device according to any of claim 1, wherein the light attenuating element (11) is a filter.

5. The device according to claim 3, wherein the light attenuating element (11) is a coating on a closure disc (4) for the gas-bearing region.

6. The device according to claim 5, wherein the coating is arranged on the inner side of the closure disc (4) facing away from the gas-bearing region.

7. The device according to any of claim 1, wherein the light receiving device (13) has a light trap (9) in the beam path of the measuring beam (2.1).

8. The device according to any of claim 1, wherein the first light receiver (8) is a first photosensitive element and/or wherein the second light receiver (12) is a second photosensitive element.

9. The device according to claim 1, wherein the second light receiver (12) is arranged at a distance from the first light receiver (8).

10. The device according to any of claim 1, comprising a measurement cell having elements (1) to (12), wherein the measured gas is directed to said measurement cell and is passed therein through the measurement volume (5.1).

11. The device according to claim 10, wherein the measured gas is heated to vaporize condensed particles.

12. The device according to claim 10, wherein purge air flows through specially arranged openings.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0027] The present invention will be explained in more detail in the following by way of the attached drawings. In the drawings show:

[0028] FIG. 1 an example of an embodiment in a roughly schematic longitudinal section.

DETAILED DESCRIPTION OF THE INVENTION

[0029] From a light source 1 a light beam 2 is emitted, most of which passes through a beam splitter 3 and a closure disc 4 into a gas-bearing region in which the gas to be measured is located or through which the gas to be measured flows. The light transmitted through the beam splitter 3 forms a measuring beam 2.1 that impinges on dust particles 5 in a measurement volume 5.1 in the gas-bearing region and generates scattered light 6 which is imaged through a lens 7 onto a first light receiver 8. The non-scattered portion of the measuring beam 2.1 is absorbed in a light trap 9.

[0030] In the beam splitter 3, a portion of the light beam 2 is split off as a reference beam 10 and, after passing through a light attenuating element 11, passes through the same closure disc 4 and the same lens 7 as the scattered light 6, but impinges on a separate second light receiver 12. The first light receiver 8 is a first photosensitive element. The second light receiver 12 is a second photosensitive element. Instead of one single lens 7, there may also be a plurality of lenses. Furthermore, instead of the lens 7, there may be an objective lens comprising one or more lenses. The components 7, 8, 9, 12 are parts of a light receiving device 13.

[0031] The light source 1 is, for example, a laser or an LED.

[0032] With this device, a scattered light signal proportional to the dust content in the measured gas and a reference signal of the same order of magnitude with respect to power can be measured simulta-neously. The necessary attenuation of the reference signal is provided by the beam splitter 3 with a low uncoupling and by the light attenuating element 11. The light attenuating element 11 is a coating on or in front of the closure disc 4.

[0033] It is particularly simple and advantageous to use a prism as beam splitter 3. As is known to the person skilled in the art, about 4% of the light is reflected at an air-glass transition at perpendicular incidence, so that the uncoupled portion of the light after two reflections accounts for about 0.16% of the portion of the transmitted light. Thus, to achieve six orders of magnitude of attenuation, the light attenuating element 11 need only have 0.1% transmission. Such coatings represent the state of the art and are widely available.

REFERENCE SYMBOL LIST

[0034] 1 Light source [0035] 2 Light beam [0036] 2.1 Measuring beam [0037] 3 Beam splitter [0038] 4 Closure disk [0039] 5 Dust particles [0040] 5.1 Measurement volume [0041] 6 Scattered light [0042] 7 Lens [0043] 8 Light receiver [0044] 9 Light trap [0045] 10 Reference beam [0046] 11 Light attenuating element [0047] 12 Second light receiver [0048] 13 Light receiving device