Arciform photo sensor asssembly

Abstract: An arciform photosensor assembly for use in an optical apparatus for detecting the radial intensity distribution of light scattered, for instance, from particles suspended in a fluid medium. The assembly includes three groups of arciform photosensor to be used for adjusting the optical axis of the optical apparatus in which this arciform photosensor assembly is used as a light detector.

Description: The present invention relates to an arcuate photosensor assembly for use in an optical apparatus for measuring the intensity distribution of light scattered forward by particles suspended in a fluid medium. For instance, among various means for detecting the size distribution of particles, there is known a method based on a theory about the small-angle light scattering by particles suspended in a fluid medium. Conformably to the method an optical system as shown schematically in Figure 4 is employed in combination with a photosensor assembly as shown in Figure 5. According to Figure 4, the optical system consists basically of a light source 1 such as a laser, lens assembly 2 for providing a light beam F having a desired thickness, a transparent flow cell 3 in which a suspension suspending sample particles is made to flow, a Fourier-transform lens 4 and a photodetector 5a made up of an assembly of concentric semicircular photosensors S i (i=1, 2,...., N) as shown in Figure 5. A similar assembly of photosensors to measure radial light distribution is described in U.S. Patent Specification US-A-4 150,360, which also shows a semicircle of wedge-shaped sensors to measure angular (circumferential) light distribution. In the optical system of Figure 4, the light beam F incident into flow cell 3 is scattered or diffracted by the sample particles, and then focused circularly on the detector 5 by the Fourier-transform lens 4, thus forming a circular image whose intensity varies in the radial direction. The radial-directional intensity distribution is detected by the above N concentric semicircular photosensors S i , and then mathematically analyzed by a micro-computer (not shown) in accordance with the Mie scattering theory and/or the Fraunhofher diffraction theory to finally give the size distribution of the sample particles. In such an optical system, that substantially constitutes an apparatus for detecting the intensity distribution of light scattered forward by particles suspended in a fluid medium, it is essentially important to adjust the direction of the light beam B so as to be directed precisely to the common centre of the concentric semicircular photosensors S i . It also is important to adjust the light beam B so as to have a desired thickness. The direction and thickness of the beam B have conventionally been adjusted through directly watching the beam with the eye or by using a special jig. However, the visual method of adjustment is harmful to the eye, while the use of a jig is often troublesome and inconvenient. Objects and Summary of the Invention The present invention aims at eliminating such disadvantages involved in the adjustment of the light beam in such an optical apparatus for detecting the intensity distribution of light scattered forward by the particles suspended in a fluid medium. An object of the present invention is, therefore, to provide an arcuate photosensor assembly improved so as to make it possible for an incident light beam to be directed precisely to the common centre of the arcuate photosensor assembly without watching the light beam with the eye. Another object of the present invention is to add to such an improved arcuate photosensor assembly a further function of making it possible for an incident light beam to be adjusted, without watching the light beam with the eye, so as to have a predetermined thickness. According to the present invention there is provided a photo-sensor assembly for detecting the radial intensity distribution of a light beam falling on the assembly, the assembly including a main group consisting of a plurality of concentric arcuate photo-sensors whose outputs represent the intensity at different radii, characterized by first, second and third auxiliary groups each consisting of a plurality of arcuate photo-sensors of different radii concentric with the sensors of the main group, the photosensors of the third group having radii which are equal to those of the photosensors of the first and second groups, the first and second groups being located within the main group and the third group outside the main group. Thus, the assembly not only has some of its successively adjacent constituent arcuate photosensors divided into two groups, preferably having the same centre angle but also is further provided with a third group of concentric arcuate photosensors whose common centre coincides with that of all the other arcuate photosensors. It is preferable that the first and second groups of arcuate photosensors and the third group of arcuate photosensors have the same centre angle. In this case, if all the corresponding photosensors among these three groups respectively output signals of the same intensity by being irradiated with a light beam having a cross-sectional radius not larger than the radius of the outermost photosensors belonging to the three groups, it is confirmed that the light beam is directed precisely to the common centre of the arcuate photosensor assembly. In the case that the centre angles of different photosensor groups are not equal to one another, whether or not the light beam falls on the common centre can be confirmed by normalizing the photosensor outputs from the different groups with their respective centre angles. After the light beam has been made to fall on the common centre of the arcuate photosensor assembly, the light beam can be further controlled to have a desired thickness by adjusting the beam thickness so that signals are not outputted from any one of the photosensors whose radii are larger than the value corresponding to the desired thickness. Brief Description of the Drawings In the following the present invention is described in further detail in reference to the accompanying drawings, in which: Figure 1 shows the frontal view of an embodiment of the present invention; Figure 2 shows a partial optical system illustrating a way of adjusting the light beam with respect to its direction and thickness; Figure 3 illustrates the operation of the present invention; Figure 4 schematically shows an optical apparatus for detecting the size distribution of particles suspended in a fluid medium; and Figure 5 shows a conventional arcuate photosensor assembly. Detailed Description of the Invention As shown in Figure 1, the photodetector 5 according to an embodiment of the present invention includes a plurality of concentric arcuate (semicircular) photosensors S i having a centre angle of 180° similarly to a conventional photodetector 5a (Figure 5), except that some of the photosensors are made to have very thin width and divided into two separate groups A and B having the same centre angle of 90° in substance. In the groups A and B the photosensors are labelled S A1 , S A2 ,....,S Am ; and S B1 , S B2 , .... S Bm , respectively. As to the arcuate photosensors belonging to the groups A and B, the radius of curvature of the outermost ones is not smaller than the largest radius expected in the light beam to be used, while that of the innermost ones is not larger than the smallest radius expected in the light beam. Further, the photodetector 5 according to the present invention is provided with a third group C of arcuate photosensors. The group C, which is the same as the groups A and B both in the constitution and the centre angle, is located symmetrically with respect to the common centre P of the three groups A, B and C. With this photodetector 5 substituted for photosensor 5a in Figure 4, and with the flow cell 3 and the lens 4 removed from Figure 4, the optical system shown in Figure 4 is reduced to such a simple optical system as shown in Figure 2. In this optical system, if the light beam is not directed to the common centre P of all the arcuate photosensors, output signals from the photosensors of the groups A, B and C vary and generate three curves P a , P b and P c as shown in Figure 3(b) with respect to the radial distance from the common centre P. If the beam F is deflected upward from the common centre P, the output curves P a and P b coincide with each other and the curve P c falls down at a radial distance shorter than the radial distance where P a and P b fall down (Fig. 3(a). Further, if the beam F is directed precisely to the common center P, the three curves P a , P b and P c coincide with one another, as is shown in Fig, 3(c). In this case the radial distance where the three curves P a , P b and P c fall down in common means the radius of the light beam F. Therefore, a beam thickness adjustment, which is carried out by adjusting the lens assembly 2 (Fig. 2), can also be achieved by observing the variation of the position where the three curves P a , P b and P c fall down in common. According to the present invention, as is understood from the above description, the light beam F can be adjusted with respect to both its direction and thickness without watching the light beam F itself. The beam adjustment can be achieved only by observing the signals outputted from the photsensors belonging to the three sensor groups A, B and C. Although the three sensor groups A, B and C have the same center angles in the above embodiment, the present invention can be embodied so that the center angles of the three sensor groups are different from one another. It is needless to say that, in such an embodiment, the output signals from the photosensor should be normalized with the center angles of the groups to which the photosensors belong.

Claims: A photo-sensor assembly for detecting the radial intensity distribution of a light beam falling on the assembly, the assembly including a main group consisting of a plurality of concentric arcuate photo-sensors (S i ) whose outputs represent the intensity at different radii, characterized by first (A), second (B) and third (C) auxiliary groups each consisting of a plurality of arcuate photo-sensors of different radii concentric with the sensors of the main group, the photosensors of the third group having radii which are equal to those of the photosensors of the first and second group, the first and second groups being located within the main group and the third group outside the main group. A photo-sensor assembly as claimed in claim 1 in which the sensors of the main group are semi-circular. A photo-sensor assembly as claimed in claim 1 or 2 characterized in that the three auxiliary groups have the same centre angles. A photo-sensor assembly as claimed in claim 3 in which the centre angle of each auxiliary group is 90°.

Inventors: NIWA TAKESHI, NIWA, TAKESHI
Applicants: SHIMADZU CORP, SHIMADZU CORPORATION
Application year: 1989
Main classification: G01J1
IPC codes: G01N15, H01L31, G01N21