Patent GB-811240-A (GB)
Title: Improvements in or relating to electric supervisory systems
Inventor: DILLOW JOHN WARREN
IPC: H04Q5/00
Filed: 1956-10-12
Abstract: 811,240. Electric supervisory systems. STANDARD TELEPHONES & CABLES Ltd. Oct. 11, 1957 [Oct. 12, 1956], No. 31166/56. Class 40 (1). In a supervisory system comprising a control office connected by a common signalling channel to a plurality of field stations, the state of apparatus at the field stations capable of assuming one of two alternative states is indicated at the control office by transmitting signals each characteristic of just one station which station identifies its signal and in response to the next signal from the office transmits a reply signal identifying the station and indicating the state of the apparatus. As shown, Figs. 1, 2, 3a, 4, a field station is connected to a control office (not shown) over a common signalling channel including lines 1 and 2 which comprise mark pulse legs A and C and space pulse legs B and D, the incoming mark pulses on line 1 after detection and amplification appearing at a terminal im and the space pulses after detection and amplification appearing at a terminal is, these terminals being commoned to a third terminal ims. In a checking train T1-T6 of coldcathode tubes, the tubes T1-T5 are connected by terminals a to the terminals im, is in a manner characteristic of the particular station to respond to a particular combination of incoming mark and space pulses only, and a train T8-T13 is connected to the terminal ims and so responds to all incoming codes. As described, the fifth pulse of all codes is a mark and the station illustrated responds to a code of five mark pulses. Initially, the tubes T1, T8 and T7 are conducting. The first four pulses step the discharge in the trains along to the tubes T5 and T12. The fifth pulse fires the tubes T6, T13, the firing of T6 extinguishing the tube T7 but not T5 as it has a separate anode load from T6. The firing of the tube T13 causes the tube T14 and associated circuits to produce a positive zeroizing pulse at the terminal ir which fires the tubes T1, T8 thereby extinguishing T5 and T13, the tube T14 extinguishing itself. Thus the tube T6 is left conducting, and the next interrogation code which may be one space pulse followed by four mark pulses is then transmitted. The terminals b are connected to the terminals M or S, Figs. 3a, 4, in the manner characteristic of the field station and the conduction in the tube T6 raises the grid potential in a valve V8 so that tubes T15 and T16 receive bias due to conduction in the tube T8. The first space pulse thus fires the tube T15 which has a self-extinguishing circuit similar to that of T14 and produces a pulse which is amplified and shaped and is transmitted to the control office as a positive mark pulse on the leg C of the line 2. The arrival of the subsequent mark pulse will cause the tube T2 to conduct instead of T1 and T9 instead of T8, connections from the tube T9 being such that the tube T15 again produces a pulse. The third and fourth pulses of the code produce a similar result. The final fifth pulse fires the tubes T5 and T13 and either the tube T15 or T16 depending on the position of the relay A contact a1 in the cathode output of the tube T12, thus transmitting over the line 2 to the control office the state of the contact a1. The tube T14 again fires to fire the tubes T1, T8, and also T7 which is primed when both T6 and T13 are conducting, the firing of T7 causing T6 to extinguish removing any bias from the terminals M, S. For all subsequent code transmissions the stepping of the discharge along the train T1-T6 never reaches T6 so no outgoing pulses are produced by this field station. In a modification the state of two two-state devices at each of eight field stations may be interrogated by a code signal having five pulses. Specification 686,829 is referred to.