GB938955A - Improvements in the determination of turbidity in fluids - Google Patents

Abstract

938,955. Photo-electric turbidometers. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Feb. 16, 1961 [Feb. 18, 1960], No. 5720/60. Class 40 (3). [Also in Group XX] An arrangement for determining the turbidity of a fluid in which two beams of light, each having an identifying characteristic, are directed into a sample of the fluid in such a way that light from one beam is transmitted directly through the sample to a light detector in the path of the beam, whilst light from the other beam reaches the detector only indirectly by scatter from particles suspended or entrained in the sample, and the two component signals of the detector output corresponding to said identifying characteristics of the light beam are separated and compared to provide a measure of the turbidity of the sample. In the diagrammatic arrangement, Fig. 1, two beams from a light source 18 chopped at different frequencies by dies 19, 20 are passed via lenses 22, 23, to mirrors 24, 25, from the first of which the beam passes through an iris diaphragm 16 and the fluid in the container 11 to the photo-electric cell 14. The beam reflected from the mirror 25 passes through an iris diaphragm 17 through the fluid in the container 11 to a mirror 15 from which it is reflected back into the fluid so that light scattered from the particles reaches the photo-cell 14. The beam passing directly through the container 11 is preferably reduced in intensity by a neutral filter 26 of density 3. The chopper discs 19, 20 have different numbers of alternate opaque and transparent sectors to provide the distinguishing frequencies. The signals from the cell 14, amplified at 26<SP>1</SP>, Fig. 2, are passed to two network chains 27, 29 ... 37 and 28, 30 ... 38, including frequency discriminating filters 29, 30 and amplifying, transmission, rectifier and smoothing circuits. The outputs from the rectifier-smoothing circuits 37, 38 are passed to a double logarithmic bridge circuit 39 connected to a suitably calibrated centre-zone recorder 40. A practical embodiment corresponding to Fig. 1 is shown in Figs. 6, 8 in which light from a lamp 18a mounted in a socket 47 is interrupted by discs 19a, 20a, driven by a motor 21a, the beams passing through adjustable lens assemblies 22a, 23a, to the mirrors 24a, 25a, a neutral filter 26a being included in the assembly 22a. The beam from mirror 24a passes through diaphragm 16a opposite an aperture 69 of the container 11a, Fig. 8, to a photo-cell mounted on support 61 and opposite aperture 67. The second beam passes through diaphragm 17a opposite an aperture 66 and to a mirror 71 closing aperture 68 and effecting reflection of the beam back into the container 1 1a to be scattered by the particles of the fluid. The circuit arrangement according to either of the transmission chains 27 ... 37 and 28 ... 38 is indicated in Figs. 5A ... 5C (not shown), and suitable values for the various components are indicated in the Specification.