Patent GB-843916-A (GB)
Title: Electric tele-control systems
IPC: G08G1/081
Filed: 1956-05-18
Abstract: 843,916. Traffic-light controllers. EASTERN INDUSTRIES Inc. May 18, 1956 [May 25, 1955], No. 15659/56. Class 118 (2). A traffic control system comprises a master controller transmitting two polyphase signals of slightly different frequency and a station controller arranged to derive two single-phase outputs one from each of the polyphase signals, and to give an output when the outputs coincide in phase. The timing of the control cycle is thus obtained and also the offset of the control cycle from that of the master. A single-phase reference frequency may be used if no offset is required. The cycle is split into timed parts by further single-phase deriving circuits and the selection of these circuits may be made at the master controller. The offset times may be altered progressively by means of a homing potentiometer at the station controller (see Specification 843,917). Parts of the cycle are under control of a local timer at each station. Master controller.-This comprises a constant-frequency 3-phase generator and a differential generator, together (if desired) with switches controlling relays at the stations. It transmits a 3-phase reference frequency (FR) and a slightly different variable (control) frequency (FC). Station controller.-The single-phase deriving device is a circular potentiometer with deltaconnected resistances fed by the 3-phase supply at points 120 degrees apart. The take-off arms are 180 degrees apart (see for example PR20). A single-phase output is derived by PR 20 from FR and by suitably altering the potentiometer setting this can have any desired phase relation to a selected one of the 3 phases. This control determines the offset of the station timing cycle. The output thus derived is formed into a spike pulse and passed to a coincidence gate CG1. The other input to the gate is from another spike pulse forming network 53 and this is derived from a selected one of potentiometers PR21, PR22 or PR23. These potentiometers derive a single-phase output from the 3- phase signal FC. As shown PR21 is connected to 53 through banks LS21 and LS22 of a fourbank stepping sequence switch driven by a conventional stepping magnet MM. When the outputs from PR20 and PR21 coincide a series of spike pulses in coincidence opens the gate CG1 to energize a relay 62 and actuate MM. This series of spike pulses is of sufficiently high frequency to hold 62 until they are sufficiently out of phase to close the gate. This prevents multiple operation of MM on one series of coincidence pulses. When 62 breaks MM steps and moves banks LS21, LS22, LS23, LS24 one step. LS24 alters the traffic light display one step in known manner. The sequence switch is assumed to have 7 contacts, 3 of which on LS21 and LS22 connect in potentiometers for operation as above described. In the other positions no input is provided to the spike former 53 and instead the stepping magnet MM is controlled by a relay 76 through contacts 96, the relay being controlled by a neon timer 75 and capacitor 74, the latter charged through selected resistances 81-84 each being effective for one step of the sequence switch. It is obvious that the sequence will be controlled in part by the master controller through potentiometers PR20-PR23 and in part by the local timer and the green and red indications can be spread over a master controlled and a station controlled period, the former varying with the cycle time, the latter remaining constant.