GB853605A - Improvements in apparatus for controlling the delivery of measured quantities of material - Google Patents

Abstract

853,605. Automatic feed weighers. LANCASHIRE DYNAMO ELECTRONIC PRODUCTS Ltd. Feb. 23, 1959, No. 6163/59. Class 143 Apparatus for controlling the delivery of material feeds the material to a measuring device, such as a weighing machine, which operates in response to the delivery of a certain quantity of material thereto to cut off the feed, and incorporates a time delay device by which the time lag between the operation of the measuring device and the cut-off of the feed is made to depend on the rate of delivery, the delay device providing a delay which is automatically made a constant fraction of the time taken to deliver the quantity of material necessary to operate the measuring device. The invention is described with reference to an automatic feed weigher in which a conveyer feeds wool to a bucket on a weighbeam, a capacitor being charged at constant current from the initiation of the feed to the time the weighbeam tilts, the delay of cut-off being defined by the time taken to discharge this capacitor at a rate greater than the charging rate. In the circuit shown, microswitch 11 is closed by the weighbeam when the weighbucket empties and energises relay A whose contact a 1 closes to engage the conveyer clutch while contact a 2 initiates charging of capacitor C, the charging current flowing through resistor 19 and rectifier 17 and being maintained substantially constant by virtue of the fact that the pentode V1a, cathode follower V1b and capacitor C constitute a feed-back loop whereby the potential of the grid of V1a, and hence the potential drop across resistor 19, is held substantially constant. When the potential of the cathode of V1b rises above that of the wiper of potentiometer 10, relay B operates to lock the clutch by means of contact b. When the weighbeam tilts, microswitch 11 opens, relay A drops out and its contact a 1 opens while a 2 moves into the position shown, so that capacitor C discharges through resistor 18 and rectifier 16 until the potential of the cathode of V1b falls below that of the wiper of potentiometer 10, when the clutch is disengaged by the opening of contact b. Potentiometer 10 is set so that the time taken to complete the discharge of capacitor C, at the rate determined by the value of resistance 18, after relay B has operated is equal to the "over-run" time of the conveyer (i.e. the time taken for it to come to rest after the clutch is disengaged). As an alternative to the circuit shown, the time delay device may comprise a cam rotated at a constant speed during the loading of the weighbucket until the beam tilts and then driven in the reverse sense at a higher speed to effect stopping of the conveyer when the cam returns to its initial position.