Patent GB-811422-A (GB)
Title: Improvements in or relating to remote indicating and recording systems
IPC: G01G23/375
Filed: 1954-03-12
Abstract: 811,422. Electric signalling systems. LANCASHIRE DYNAMO ELECTRONIC PRODUCTS Ltd., and WHITLOCK, R. H. June 13, 1955 [March 12, 1954], No. 7252/54. Class 40 (1). [Also in Group XXXVII] In an apparatus for signalling the position of a pointer, particularly of a weighing machine, an arm 5 is attached to the pointer spindle 4 and carries a flag 8 which intercepts the light beam from a source 7 when a follower arm 1 carrying a photo-cell 6 and the source 7 is moved into alignment with the arm 5. A further flag 9 is so fixed that it uncovers the light source as soon as the follower moves from its zero position. The follower 1 is driven through a gear-box 10 by a reversible A.C. motor 11, Fig. 3, which also drives an impulsetransmitting device 17. The spindle 2 of the follower 1 controls limit switches 18, 19, the switch 18 engaging its left-hand contact, Fig. 3, when the follower is in its starting position and its right-hand contact when the follower reaches the limit of its movement, whereas the switch 19 engages its left-hand contact in the starting position and its right-hand contact as soon as the follower moves from its starting position. A zero limit switch 20 consisting of a fine wire contact is closed when the pointer is in the zero position, and a " stop-fraud " switch 21 closes one or other of its contacts when the pointer is moving in one direction or the other and opens both contacts when the pointer comes to rest. To initiate the operation the circuit is closed at 23 to energize relay C through contacts q3, dl, b1 and switch 19, relay B being energized because switch 21 is open. Relay C is held over c1 and starts the motor by connecting the supply 22 through c5, switch 18, and q1. As the follower moves from zero the photo-cell 6 acts to remove a positive bias which is normally fed to the right-hand grid of V1 through a resistor 25 and the consequent reduction of potential on the left-hand grid of V2 causes a positive potential to be applied to the grid of a thyratron V3 and thereby establishes a circuit for the transmission of impulses from the transmitter 17. It also increases the anode current of the right-hand side of V2 to operate relay A. Switch 19 completes a feed circuit for relays E and F, but F cannot operate until A has been operated and then released. As the follower passes the position of alignment with the arm 5 light is cut off from the photo-cell 6 and the right-hand grid of V1 receives a positive potential which through V2 reduces the potential of the grid of the thyratron V3 to render it non-conductive to stop the transmission of impulses. Relay A is released, causing F to operate and through,f4 to lock V3 in the non-conducting condition. Contact f6 opens and f5 closes to reverse the motor and return the follower to zero at which position switch 19 breaks the circuit of relays E and F and the motor circuit is opened at contacts c5,f5. Relay Q is energized whereby a direct current from input 16 is applied through the motor windings to stop the motor. Relay B is controlled by the switch 21 through a delay network RC and prevents operation of relay C until the pointer is at rest. The left-hand grid of V1 normally is at a positive potential, regulated by a stabilizer valve S and a diode, and the cathode is connected to the left-hand grid of V4 so that relay B is energized when the pointer is at rest. When either of the contacts 21 closes the grid potential falls and relay B is released. Relay J is operated when switch 20 is closed when the pointer is at zero and through j2 releases B. If the pointer moves after relay C has operated, the release of relay B energizes relay G and thereby relay F to return the follower to zero. Contacts g1, g2 may control an alarm and a device for cancelling the weight indicating signal. Specification 811,421 is referred to.