Patent GB-650691-A (GB)
Title: Improvements in or relating to electrical transmission systems
IPC: G08B9/06
Filed: 1947-06-14
Abstract: 650,691. Electric selective signalling. CHADBURNS (LIVERPOOL), Ltd., and BREWERTON, A. E. June 14, 1947, Nos. 15711 and 15712. [Class 40 (i)] In an order-telegraph or other follow-up system comprising a transmitter-receiver at each station, a coincidence switch at each station is arranged to be operated by the movement into and out of coincidence of the station transmitter and receiver, the coincidence switch functioning to control the electric supply to the system or/and a device for locking the motor driving the receiver, and a delay device is provided to delay cutting off the electric supply or/and locking of the receiver rotor after coincidence is reached. As shown, Fig. 1, each transmitter comprises three contact arms 62, 63, 64 adapted to wipe over a circular contact blank consisting of relatively long arcuate contacts 52, 53 connected respectively to the positive and negative supply poles and sets of three short contacts arranged between the adjacent ends of contacts 52, 53. The middle contacts 54, 55 of these sets are " dead " and the contact pairs 56, 58 and 57, 59 are connected, respectively, to the contacts 52, 53 through resistances 60. This arrangement gives 15-degree steps of the transmitter rotors to which the resultant fieldtype receivers selectively respond. The receivers each comprise the usual mesh connected stator 51 and permanent magnet rotor carrying a pointer 68 and a toothed sector 81 for locking the indicator by means of a spring- biassed plunger 72. Normally, with both indicators 68 in step with their associated transmitter operating handles 61, power is disconnected from the circuit by open switches 70, which are closed only when there is lack of coincidence between the transmitter and receiver associated therewith. Upon operation of transmitter B, for example, the associated coincidence switch 70 closes to energize a slowto-release relay 71 which connects the D.C. source to the system, operates an audible signal 73 and electromagnetically retracts the locking plungers 72 to release the receiver pointers 68. At the station E the operator acknowledges the order by moving his transmitter to the new position thereby operating the receiver at B, the system reverting to the normal de-energized condition when both coincidence switches subsequently open. Receiver construction, Figs. 6, 7. A receiver suitable for the system of Fig. 2 comprises a permanent magnet rotor 69 carrying two counterbalanced pointers 68, 101, the latter being extended at right angles as in Fig. 4 (not shown), to increase the viewing area. The locking mechanism for the pointers comprises a perforated disc 103 secured to the receiver rotor and a spring-biassed locking pin 105a adapted to engage in the disc perforations. The pin is carried by the armature of a magnet 104 energized, as shown in Fig. 1, when the coincidence switches are closed to release the rotor. Mounted coaxially with the rotor is a forked member 107, Fig. 7, which is moved with the transmitting handle 61 and carries the coincidence switch 70, the contacts 108, 109 of which are closed by the notched cam 103 carried by the rotor shaft 99, for all positions except that of coincidence. The coincidence switch may, alternatively, be carried on a disc, Fig. 2 (not shown), movable with the transmitter handle, the switch being opened in the coincidence position by a cam movable with the receiver pointer. Modifications. The unlocking electromagnet 104 may be provided with contacts so that it will function also as the relay 71, Fig. 2. The number of steps of the receiver may be doubled by providing each of the three transmitter brushes with two contacts spaced 15 degrees apart and connected together by a resistance, Fig. 8 (not shown), the mid-points of the resistances being connected to the receiver. Further steps may be obtained by the use of further short contact segments connected by resistances to adjacent segments or, by increasing the number of phases. The contacts may be arranged unsymmetrically where non- uniform steps are desired. The pointers may be replaced by lamps selectively lit according to the order sent by a brush moved by the receiver rotor over a series of contacts connected to the lamps. The receiver permanent magnet rotor may be provided with a cogged soft iron disc armature co-operating with a fixed toothed concentric ring to facilitate centring of the rotor in its various steps. The rotor may carry the three " phase " windings in which case the coil 112 provides the stator magnetic field. The invention may be used with a tachometer or torque responsive device to indicate remotely the speed of a shaft.