Patent GB-868962-A (GB)
Title: Improvements in or relating to the feeding of granular materials capable of flowing
IPC: G01G11/08
Filed: 1956-05-29
Abstract: 868,962. Automatic rate of feed control systems. DENNIS, G. P. May 22, 1957 [May 29, 1956], No. 16511/56. Class 38 (4). The mass rate of flow of granular material from a hopper 10 (see Fig. 1) is automatically controlled by incorporating in the conveyer 12 fed by the hopper a weighing section 14 including load cells 15 such as resistance or crystal strain gauges which deliver an electric signal amplified at 16 and fed to an indicator 17 with manually - adjustable upper and lower switch contacts closed when the feed-rate leaves a desired range to control through unit 18 the supply to an electrically-operated vibratorfeeder 11. Fig. 2 shows one form of controller 18 in which the operating coil 20 of feeder 11 is supplied from an autotransformer 24 via line 22, resistor 26 being normally in circuit; this resistor may be shorted out by contacts 42 to increase the supply to coil 20 and hence increase the feed rate, or a further resistance 27 may be brought into circuit by opening contacts 41 to decrease the feed rate. Contacts 41, 42 are operated by " decrease " and " increase contactors 36 and 38, respectively, on closure of switch contacts 33, 32 of indicator 17; these contactors also close circuits via contacts 48, 51 to a reversing motor 43 which operates through mechanical linkage 44 to decrease or increase the output voltage of autotransformer 24, the linkage 44 including " lost motion " so that small deviation of flow rate will be corrected by resistors 26, 27 without adjustment of the autotransformer. The controller also includes main and auxiliary contactors 29 and 31 with contacts 28, 30 between the supply 19 and auto-transformer 24; main contactor 29 is energized through start button 72 (it has self-holding contacts 73) and released by " stop " button 74. The auxiliary contactor 31 is energized by a timing unit 82 through normally closed contacts 93, which are opened by the energization of a relay coil 89 after a time delay adjustable by timer 85; this relay is energized through either of contacts 80, 81 on the increase and decrease contactors. Hence if either or both of these contactors remain operated for a predetermined time (10-60 seconds, for example) the relay coil 89 will operate to open contacts 93 and hence contacts 30 to switch off the feeder; hold-off contacts 91 then maintain the coil 89 energized until manual re-set switch 88 is opened. Timer indicator and warning devices 97 and 96, operated by contacts 95, 94 are provided. A modified controller is described in which the motor 43, in addition to altering the A.C. output from a transformer, also alters the amplitude of a rectified A.C. voltage superimposed on it. The feed from each of a number of hoppers on to a common conveyer may be controlled by an individual feeder, the supply to which is adjusted in the above-described manner, in this case contactors 36 and 38 have each a pair of contacts 41 or 42 for each feeder circuit, and motor 43 is coupled to a number of auto-transformers each associated with a feeder. These couplings may include releasable clutches to allow for adjustment of the individual feedrates to obtain a desired proportion in the mixture on the conveyer.