GB1122809A - Device for measuring turbidity in fluids - Google Patents

Abstract

1,122,809. Photo-electric determination of turbidity. IMPERIAL CHEMICAL INDUSTRIES Ltd. Nov. 30, 1965 [Nov. 4, 1964], No.44922/64. Heading G1A. Turbidity detection apparatus includes two photo-conductive cells, one located to receive light transmitted from a source through a fluid, and the other receiving light scattered by the fluid, and means to compare the resistances of the cells. The device has application in, for example, the measurement of the cloud point (i.e. the temperature at which separation of phases occurs). A sample liquid is contained in a test cell 7, Fig. 1, contained in a light-proof box 5 in which are arranged two photo-resistors 4, 6 e.g. cadmium sulphide cells, at right angles to one another, a light beam being directed at one of the cells, through the liquid. The cells from two arms of a Wheatstone bridge circuit, Fig. 2 (not shown) and the other arms of variable resistance are adjusted to balance the bridge such that the light spot in the galvanometer (G), arranged across the bridge, falls on to a photo-cell and energizes a heater to heat the sample. At the cloud point the liquid becomes turbid and the bridge out of balance due to the difference in the detector resistances. The galvanometer light spot moves and the heater is cut off. The temperature of the sample is then read, by the operator having been alerted by a visual or audible alarm, to read a thermometer immersed in the liquid or a galvanometer (G 2 ) forming part of a further Wheatstone bridge including a thermistor immersed in the liquid, Fig. 3 (not shown). Automatic recording of the cloud point is possible. The galvanometers (G 1 or G 2 ) being replaced by the channels of chart recorders. The off-balance current of the photo-cell bridge may be fed to a transistor amplifier feeding an ammeter and a trip relay to operate the warning device and switch off the heater. Other applications mentioned are measurement of size particle distribution of solid particles in a liquid, particularly in a centrifuge system, solubility by investigating a suspension at different dilutions, and analytical studies by precipitation.