Patent GB-1089299-A (GB)
Title: Improvements in or relating to electrical communication systems
Inventor: GWILLIAM JOHN
IPC: H04Q9/14
Filed: 1963-10-16
Abstract: 1,089,299. Electric selective signalling. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. Oct. 7, 1964 [Oct. 16, 1963], No. 40821/63. Heading G4H. A control and supervisory system comprises a central station and several field stations connected over a common channel selection signals in a 2-out-of-5 code, stored at the central station, being transmitted to select one of the field stations, a check signal in a 3-out-of-5 code being returned by the field station, there being means at the central station to combine the transmitted and returned signal to obtain a 5-out-of-5 -code check signal. The common channel VLF, Fig. 1, is a voice frequency link and there are a hundred field stations OSTNX controlled from the central station CE. A " mosaic diagram " MD at the central station comprises an array of small panels, one for each field station. Each field station panel consists of an array of sub-units each of which may have a two-position key to select its associated unit, e.g. a circuit-breaker. The present state of each unit of a field station is stored in CS on a toggle circuit connected with the two-position key so that, if the key is in a position different from the toggle, a lamp lights behind the key. The store CS also includes a selection matrix operable by the selector key to produce coded signals representing four digits, two corresponding to the selected field station and two to the selected unit at the field station. When a selector key is operated so as to be at variance with the corresponding toggle of store CS the condition is detected by resistor gates and a station selector indicator SS1 produces a signal to start pulse unit PU which causes a fourstage control counter CC to control the timing and order of transmission of the coded signals. Voice frequency tones corresponding to these signals are transmitted by transmitter CVFT to all the field stations. Receivers at the field stations convert the tone combinations to D.C. combinations which are applied to a station gate adapted to respond only to the two digits identifying the field station and pass subsequent digits via distributer ID to the function selector FSC where it may be stored, for example on a hundred toggles. The digits sent partially select other field stations and these are reset by the return signal produced by the selected field station. The setting of the function selector FSC steps the distributer ID to the next position connecting function discriminator FI to station gate SG. A counter in this gate is now supplied with pulses from pulse unit PUS to cause transmission of the check signal in the form of the complement of the 2-out-of-5 coded signal transmitted to the field station this 3-outof-5 check signal is received at the central station in error detector ED where it is added to the transmitted 2-out-of-5 signal. If a correct 5-out-of-5 signal is produced the station selected indicator SCI is operated causing a lamp to light indicating to the operator that the field station has been properly selected and the command button may be pressed to cause the selected function to be effected. The signal from the command button is gated with the output of the station selected indicator SCI in the station selector indicator SSI and the output starts the pulse unit PU. In the manner described above, this causes the re-transmission of the selection signals. The distributer DI is now in its third position and the field station equipment is set up again as before, except that the function control digits pass to the function operate gates OG where the function signal is checked against that stored from the first transmission. If the signals compare, the function is effected. A change at the field station is detected by function indicator FI and pulse unit PUS started again to return the field station signals again and the function signals all in 3-out-of-5-code. At the central station these signals are decoded in the display decoder DD and cause the corresponding store in MD to be changed. The lamp, lit to indicate a discrepancy between the store and the selector switch, now goes out to indicate that the selected function has been effected.