Patent GB-846094-A (GB)
Title: Improvements in or relating to weight or composition factor measuring apparatus for sheet materials
Inventor: WOOLFSON LOUIS ARTHUR
IPC: G01N23/203
Filed: 1956-04-07
Abstract: 846,094. Photo-electric measurement of sheet materials. DUNLOP RUBBER CO. Ltd. March 21, 1957 [April 7, 1956], No. 10676/56. Class 40(3). Apparatus for the measurement and control of the weight per unit area or the composition of rubber sheet 11 passing over a steel calender bowl 10 comprises two sources of beta radiation of different energy levels, viz. strontium 90, (reference 12) and thallium 204, (reference 13) shielded at 14 and 15, and ionization chambers 16 and 17 to detect radiation back-scattered from the rubber sheet. Alternatively, transmitted gamma radiation may be measured instead of back-scattered beta radiation. Channel A determines the weight per unit area of the sheet and is subject to correction by channel B which determines the composition and is in turn corrected by channel A. A potentiometer 1 a is wound to follow a curve representing the high energy source 12 and a potentiometer 2a wound to follow the curve of the low energy source 13. A potentiometer 1b is wound to obey the law connecting voltage from the ionization chamber for the low energy source and the composition factor at constant weight and a potentiometer 2b is wound to follow the law connecting voltage from the ionization chamber for the high energy source and composition factor at constant weight. Potentiometers 3a and 3b are wound so that their resistance change with rotation is linear. The sliding contacts of potentiometers 1a, 2a and 3a are ganged together on a shaft 4a which is connected to the shaft of a servo-motor 18, one end of each potentiometer winding being connected to a common earth. The sliding contacts of potentiometers 1b, 2b, 3b are similarly ganged on a shaft 4b connected to a servomotor 19. Potentiometer 1a is connected to a servo-motor circuit 20 so that any difference between the voltage supplied by amplifier 21 and that at the sliding contact of potentiometer la causes servo-motor 18 to rotate shaft 4a and adjust the voltage to agree with that from the amplifier. Channel B is similarly connected. Fixed voltages V2a and V2b are fed to the ends of potentiometers 2a and 2b so that the appropriate voltage is fed to the potentiometer with which their sliding contacts are connected. Fixed voltages V3a and V3b are fed to potentiometers 3a and 3b, the sliding contacts of which are connected to meters 24 and 25 to measure deviation in weight per unit area and composition factor respectively of the sheet 11. The output of the measurement is used to control the weight per unit area of the sheet by altering the nip of the calender bowls. Instead of indicating variations in weight per unit area from a predetermined value at meter 24 a meter may be provided to measure directly the voltage of the sliding contacts of potentiometer 3a calibrated in divisions of weight per unit area. A similar modification may be applied to the composition factor meter. Alternatively potentiometers 1b  and 2b may be ganged together on the shaft of another servo-motor fed by an amplifier which amplifies the difference between voltages fed from the sliding contacts of potentiometers 3a and 3b. (Fig. 3 not shown).