Patent GB-548747-A (GB)
Title: Printing telegraph system
IPC: G08B25/00
Filed: 1941-07-04
Abstract: 548,747. Fire and police alarm systems. CREED & CO., Ltd. July 4, 1941, No. 8456. Convention date, July 13, 1940. [Class 40 (i)] [Also in Group XL] The central station of a police or fire alarm system comprises, in addition to an ordinary printing telegraph transmitter and receiver 31, a transmitter which sends variable messages in an invariable framework. For example, as shown in Fig. 5, the message may consist of three repetitions of a group of letters or figures variable in number and selected by a single one of a group of keys 65 and a group of four figures individually selected by keys in groups 96-99 and finally the time of day, the double dashes, hyphens and colon separating different parts of the message being sent by means of permanent wiring. The ordinary and special sets are duplicated and testing arrangements are provided. The messages are recorded locally and repeated into a number of lines eaeh of which has several substations. Preliminary operations. Operation of preparatory key 122, which locks itself, energizes 47 to reverse current in the home recorder 32 and the outgoing lines and in relay 44 which energizes 45, 46. The home repeating relay 40 is thus made effective on the recorder 32 and tell-tale lamp 35 and motor 34 in the local set 31, and. lamp 176 and mtor 177 in the special transmitter are energized. The operator then presses key 123 momentarily to operate 76 and so couple the transmitter shaft 74 to the motor. Each rotation of the shaft gives a step to a cam shaft 80 which at once changes over the springs controlled by cams 180-183 but leaves the springs controlled by cam 185 in the position shown until a later stage. At each rotation of the transmitter, contacts 126 give an impulse to the stepping magnet 88 of a sequence switch 60 which determines the order of transmission of the signals and the nature of the invariable signals. Transmission of message. During the first trip of the sequence switch, the signals " space " " figure shift ", " double dash ", " figure shift " are sent by Baudot apparatus 72 in positions 1 to 4, a group of letters or figures depending on the operated key in group 65 in positions 5 to 11, " figure shift " and " hyphen " in positions 12 and 13, four figures depending on the keys operated in groups 96 to 99 in positions 14 to 17 and then " double dash " and " space ". By this time, contacts 128 have been opened by cam 185, and on the operation of contact 126, the sequence switch races over its remaining terminals by self interruption. The second and third trips cause similar signals to be sent but by the time the 21st terminals are reached on the third trip, contacts 128 are closed again to shunt the self-interrupting contacts. The switch therefore advances slowly causing signals to be sent in accordance with the positions of the time switches 67. At the end of the cycle, the operated keys are unlocked by the camshaft. Substation circuit. When the line current is reversed by the transmitter, 230 energizes 233 which starts the motor and energizes a recorder 255. At the same time, a lamp 235 glows and a relay 236 increases the rate at which the local battery is being charged by the mains. Signals operate the recorder magnet 231 but leave 230 in its changedover condition. Testing. Operation of key 43 substitutes the spare ordinary and special sets for the normal ones to enable the latter to be tested, and makes alternative circuits for the control of the repeating relay 40 by the transmitters 33 and 72.