GB1472943A - Batch weighing system - Google Patents

Abstract

1472943 Repetitively weighing a pre-selected weight of bulk products HOUSTON CONTROLS SYSTEM Inc 20 March 1974 12483/74 Heading G1A In a force balance device for repetitively weighing a pre-selected weight of bulk products that are transported to a scale hopper 24 by means of a vibratory feed device 20, the deviation of the scale beam 30 from the horizontal is measured, Figs. 2, 3, by a stationary light source 122 illuminating a pair of detectors 128 via a stationary apertured screen in combination with a movable slit screen 124 attached to the beam. The outputs of the photo-cells 128, which are proportional to the beam's displacement is applied via an amplifier 44 to an electric motor 42 in the form of a "moving coil loudspeaker arrangement", whose coil 140 is attached to the beam. The amplifiers 44, 56, and 58 and their associated resistors are designed so that the beam is substantially maintained horizontal. Additionally the induced e.m.f. that appears across the coil whenever the beam is displaced is used to provide a further feedback signal via amplifier 58 which is proportional to the arm or coil velocity. This enables the motor to provide the equivalent of "viscous damping" to the beam. The viscous damping signal appears across resistor 59 and is summed with the voltage due to the charge in position across the resistor 46. The signal from the amplifier 44, which is proportional to the weight in the hopper 24, is fed via a 60Hz filter to a differential amplifier 72 which compares the hopper weight signal with the output of a D/A converter 74. When the inputs to the amplifier 72 are equal, the amplifier 72 turns off the feeder 20 and initiates a time delay 76 that controls a ramp generator 78. The ramp generator signal feeds two sets of logic circuits each associated with an "up/down counter" 94 or 104. The circuit associated with counter 94 uses differential amplifiers, an exclusive OR gate 88 and an AND gate to compare the weight signal with "a pre-selected signal" from a potentiometer 98. If there is a discrepency, pulse signals from a clock 92 are gated via AND gate 90 to the up/down counter 94 to effect readjustment of the D/A converter 74. In a similar fashion the speed of the feed device 20 is maintained at the maximum rate for the system by using a logic circuit to compare a pre-selected percentage potentiometer 98 signal with the output of the D/A converter 74. The circuit shown in Fig. 1, is explained in greater detail Figs. 4-7 (not shown) including an arrangement to terminate the operation of the product feeder 20 at a time before said pre-selected weight of the batch is in the scale hopper 24, to allow for the product flowing at the time of termination, thus ensuring that the final weight in the scale hopper is the pre-selected weight.