Patent GB-811421-A (GB)
Title: Improvements in or relating to remote indicating and recording systems
IPC: G01R17/04
Filed: 1954-03-12
Abstract: 811,421. Electric signalling systems. LANCASHIRE DYNAMO ELECTRONIC PRODUCTS Ltd., and WHITLOCK, R. H. June 13, 1955 [March 12, 1954], No. 7251/54. Class 40 (1). [Also in Group XXXVII] In an apparatus particularly for signalling weight measurements, the shaft of the weighing machine carries an arm 1 with a flag 7, which may have a translucent leading edge, arranged to intercept the light beam from a source 6 when a follower arm 3 carrying a photoelectric device 5 reaches a position of alignment with the arm 1. The arm 3 is mounted on a spindle 4 driven through gearing 8 by a motor 9 which also drives an interrupter 10 which transmits an impulse to remote indicating apparatus for each unit of movement of follower 3. A cam 11 is fixed to the spindle 4 and operates a limit switch whose contacts 12, 13 are closed successively as the follower 3 returns to its starting position, and closes contacts 14 if the follower over-runs the starting position. The photoelectric device 5 controls the input of the lefthand triode of V1 which is cathode coupled to the grid of the left-hand triode of V2. V2 operates as a cathode coupled amplifier, the right-hand grid being connected to potentiometer 15 which can be adjusted to make the two anode potentials of V2 equal to one another at, for example, an intensity ofillumination of the photo cell 5 of half the maximum intensity. The anodes of V2 are connected through neon tubes 16 to amplifying valves V3, V4 which control the exciting current fed to two opposed field windings 17 of the motor 9. In the position of rest of the system all relays are de-energized and the grids of valves V3 and V4 are connected through contacts a1, c1 so that the opposed windings 17 are equally energized, and the armature is short circuited by b1, c5. When the weighing machine is operated, movement of the arm 1 causes the photo-cell 5 to be illuminated to make the left-hand grid of V1 more negative. This produces a difference of potential between the anodes of V2 which, when the terminals 24 are connected by a pushbutton or the like, to energize relay A, followed by relay B causes V3 and V4 to produce a resultant excitation of the field windings 17 for forward movement of the motor. The follower 3 is driven forwards and the interrupter 10 transmits impulses via terminals 25 to a counter. As the light beam is intercepted by the flag 7 the left-hand grid of V1 becomes progressively more positive. This causes a positive pulse to appear at the right-hand grid of V1, the grid being fed from a potentiometer 20 via a differentiating circuit 21, 22. The pulse is amplified and reversed in polarity, and fed via capacitor 23 to the right-hand grid of V2 to produce a temporary reversal of the potential between the anodes of V2 and a consequent reversal of the excitation of the motor, due to the differential action of valves V3, V4, to check the speed of the motor and prevent overshooting. The system is so adjusted that as the potential of the right-hand grid ofV2 returns to its normal value, the potential of the left-hand. grid rises to that value and the motor is thus brought to rest. The release of relay B is delayed by resistor 27 and capacitor 28. Diode 29 prevents discharge of the capacitor through windings 17. When B releases relay E is energized by discharge of capacitor 30 and holds through contact e1 and through contact e2 sends a signal to the remote station. Relay C is energized and through contact c3 applies a positive potential to the left-hand grid of V2, which causes an unbalance in V3 and V4, and the motor 9 to operate in the reverse direction no impulses being transmitted since the circuit is opened by b4. Shortly before the follower 3 reaches its zero position contacts 12 are closed by cam 11 and a negative pulse is applied to the left-hand grid of V2 via capacitor 32, causing temporary reversal of the excitation of motor 9 to slow it down. Contacts 13 are closed when the follower reaches its zero position and operate relay D which short circuits the armature through d1 to bring the motor to rest. Relay E is de-energized, and after a short delay C falls causing de-energization of D, and the system is ready for the next operation. An electrostatic or electromagnetic device may be used instead of the photo-cell 5. Specification 811,422 is referred to.