GB712421A - Improvements in methods of and apparatus for the measurement of continuously flowing comminuted materials - Google Patents

Abstract

712,421. Measuring quantity of material on a conveyer photo-electrically. UNILEVER, Ltd. Sept. 26, 1952 [Oct. 2, 1951], No. 22925/51. Class 40 (3). [Also in Group XXXVIII] The cross-sectional area of powdered material on a conveyer is determined by directing a beam of light on to the material and receiving on a photo-electric cell an image of the cross section of the material formed by the intersection of the boundary of the beam and the material. As shown, Fig. 3, the boundary is formed by a light source 5 situated above the conveyer 2 on which the material passes through a housing 4. The boundary of the beam is a straight line and is formed by a four sided shroud 9 one edge of which has a lip 10 which is situated below the line filament of the lamp. The measuring photocell 12 is situated on a carrier 16 in a housing 14. The image is focused on to the cell by a lens system 18 and carrier 16 embodies a mask which restricts the area from which the cell receives light and is so arranged that its lower edge allows light to reach the cell from the intersection of the beam and the empty conveyer. A reference cell 13 is similarly mounted and is arranged to receive light from the centre of the conveyer so that the cell field is completely obscured when only small quantities of material are present on the conveyer. Circuits and operation, Fig. 5.-Either of photo-cells 12, 13 the output of which is smoothed by condenser 25 may be connected by switch 23 to a magnetic push-pull amplifier 24 in the output of which is connected full wave rectifiers 26, 26'. A milliammeter 28 and variable shunt 29 are connected between the common negative of the two rectifiers and the mid point of resistors 27 joining the positive terminals. The apparatus is calibrated by means of a standard tray of material on the conveyer and the reading of the instrument with the reference cell connected is noted so that the apparatus may later be checked for variations in emission of the light source. If the speed of the conveyer is constant the meter may be calibrated directly in flow. If not a tachometer generator coupled to the conveyer may supply a voltage to be multiplied electrically to the cell output. Control of second material in accordance with quantity on conveyer, Fig. 6.-Milliammeter 28 is replaced by a potentiometer 30 and a differential servo-amplifier receives a voltage from the slider of the potentiometer and a second potentiometer 31. The difference voltage is amplified and fed to a servo-motor 40 which brings the difference voltage to zero by adjusting the slider of potentiometer 30 and simultaneously adjusts a slider 41 of a further potentiometer controlling the speed of motor 43, and thus the feed of a second powder through a rotary valve 44. The ratio of the feed of this material and that on the conveyer is thus kept constant.