GB1347169A - Concentration measuring apparatus - Google Patents

Abstract

1347169 Photo-electric measurement of concentration YOKOGAWA ELECTRIC WORKS Ltd 10 May 1971 [21 May 1970] 13991/71 Heading G1A [Also in Division G2] The concentration of an optically active substance such as pulp or sugar in a liquid or dispersion is measured by passing polarized light through the sample and detecting the optical activity (rotation of the plane of polarization) using an analyser and a first photo-electric detector and the transmissivity of the sample independent of optical activity using a second photoelectric detector. In the apparatus of Fig. 1, light from lamp 1 is filtered, if necessary, at 2 and collimated by lens 3. A rotatable polarizer or Nicol prism 4 polarizes the light before it passes the sample cell 6. This comprises two spaced plane-parallel plates separated by spacers and provided with grooves 611, 621 on one or both internal surfaces which allow smooth flow conditions since any solid lumps can pass along the grooves and do not clog the test sections 67. The grooved parts are shielded by masks 63 so that only areas 67 of the cell are effective. Device 7 comprises a plurality of tuoular shielding members of circular, rectangular etc. cross-section, and is designed to remove any diffused or scattered light emerging from the cell 6 from the beam to be detected. The detection arrangement comprises an annular photo-cell 9 for detecting light transmitted through the sample in cell 6 and an analyser Nicol prism 8 and photo-cell 10 for detecting light whose plane of polarization has been rotated by the sample. The photo-cells are connected in the differential circuit of Fig.4 so as to measure the ratio of their outputs. The circuit is provided with a motor-driven slider 13 to balance E 1 and E 2 , in which condition the value of R of variable resistor R s represents the concentration C of optically active material in a liquid independent of colour or turbidity of the liquid. R 1 is for zeroing and R 2 for span adjustment. Calibration of the apparatus can be simply by varying the angle of polarizer 4 (or possibly analyser 8) without using a standardizing liquid. The apparatus of Fig.1 may be associated with a meter operating by scattering and transmission Fig.9 (not shown), in order individually to measure the pulp and clay concentrations in a pulp/clay mixture in a liquid. The further meter operates by using an annular cell to detect scattered light and a central circular one for transmitted light. These signals are combined to provide a ratio representing the sum of the pulp and clay concentrations. By subtracting the signal representing pulp concentration only, from the Fig.1 type meter, the clay concentration is determined. A variety of graphs are provided to explain the operation and use of the apparatus. The diffused light eliminator may be omitted if the detector 10(35) is spaced sufficiently from the cell or the spacing between the two detectors is adjusted correctly.