Patent GB-393912-A (GB)
Title: Improvements in and relating to apparatus for measuring the length of moving objects
IPC: B41F33/14
Filed: 1933-02-25
Abstract: 393,912. Gauging-apparatus. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Cockrell, W. D.; 1, Rugby Road, Schenectady, New York, U.S.A.) Feb. 25, 1933, No. 5809. Convention date, Feb. 25, 1932. [Class 106 (ii).] Apparatus for measuring the length of a moving object 1, e.g. a bar or plate, comprises a number of light beams 3 .. 6, intercepted successively by the object, which normally fall upon photo-electric cells M, A1, A2, A3, coupled to indicators B1, B2, B3 which latter are actuated to indicate the length according to the number of beams 3 ... 6 which are cut off before the object 1 ceases to interrupt the first beam 3. Assuming that the distances between the sources 7 of light are a, b, c then indicator B1 is actuated for lengths between a, b, indicator B2 for lengths between b, c, and indicator B3 for lengths greater than c. The anodes of master photo-electric device M and the auxiliaries A1, A2, A3 are connected to voltage divider 11 and their cathodes are connected to -ve line 8 through resistors 13 and to the grids of electron discharge devices 15 .. 18, the cathodes of which are wired by line 19 for heating from the secondary 20 of a transformer. The anodes 15 .. 18 are connected through resistors 23, 25 to voltage divider 10 and also through resistors 26 to the grids 28, 29, 30 of vapour electric discharge devices 31, 32, 33. The cathodes 31, 32, 33 are heated by circuit 35 from the secondary 36 of a transformer connected to divider 10 through the sliding contacts 37 of time delay switch 38. The anodes 31, 32, 33 control relays 42, 43, 44, the contacts of which are in the circuits of indicators B1, B2, B3. Relay 42 is also wired to switch 38 ; the time required for the latter to open its controlled circuit is slightly more than the time necessary for an object 1 to travel from beam 4 to beam 6. The apparatus operates as follows :-whilst beams 3 .. 6 are uncut, the resistance of each device M, A1, A2, A3 is a minimum. Because of the combined voltage drop through resistor 23 each resistor 25 due to the anode current of each device 16, 17, 18, the anode potential of the latter and of grids 28, 29, 30 is -ve with respect to point 39 and hence with respect to cathodes 31, 32, 33. Thus the devices 31, 32, 33 are inoperative to pass current and indicator lamps B1, B2, B3 remain unlit. When the object 1 cuts beam 3, device M passes a smaller current, device 15 becomes inoperative, but devices 16, 17, 18, 31, 32, 33 remain as before. When beam 4 is interrupted, device 16 becomes inoperative, so that the potential of anode 16 and grid 28 become +ve with respect to point 39. Hence device 31 passes current and relay 42 energizes indicator B1 by closing its circuit, and also energizes relay 38. If object 1 is long enough to cut beams 5, 6 whilst beam 3 is still cut, the lamps B2, B3 are also lit. Supposing, however, the object 1 has a length between b, c, then after beam 5 is cut and before beam 6 is cut, beam 3 is uncovered and device M passes more current and device 15 becomes operative again. Because of the voltage drop in resistor 23 due to the anode current of device 15, the potential of anode 18 and grid 30 become -ve with respect to point 39 and will remain so even after device 18 is disabled by the cutting of beam 6. Hence indicator B3 fails to operate and the observer will see only indicators B1, B2