Patent GB-384773-A (GB)
Title: Improvements in or relating to police, fire, ambulance and like telephone call systems
IPC: H04M11/04
Filed: 1931-11-21
Abstract: 384,773. Fire, police, &c. call systems. ERICSSON TELEPHONES. Ltd., 67, Kingsway, DOIG, P., 12, Carlton Vale, both in London, ROBINSON, E., 46, Ella Road, West Bridgford, and GREEN, B. A., 3, Bramcote Road, Beeston, both in Notting- ham. Nov. 21, 1931, No. 32291. [Class 40 (iv).] Telephone instruments at a call station have entirely distinct means of access for a number of kinds of call or classes of caller, e.g. ambulance, fire, police and public, for calls over a common line, a signal distinctive of the means of access employed being sent over the line to the distant end. As described, the invention is applied to a street pillar for use in the system described in Specification 377,407. wherein police and public use different sets at the same:call pillar, but a common set may be used for all calls. It may also be applied to a call box where different classes of callers enter by different doors, or where one class enters a door and another obtains access to the instruments through a small door without entering. One class of call may be given priority over another. The simplex, and loop conditions set up by different callers as described in the above-mentioned Specification may be used to differentiate between the callers. Construction of call pillar. The head of the pillar is of triangular prismatic form with a lamp PM and if desired a gong MC at the head. A locked door D1 gives access to the police set T, a door D2 gives access to the public set M, LS, and a horizontally hinged door D3, operable by an attendant with a special tool, gives access for inspection &c., the lighting circuit being cut off by a switch controlled by, the door. The police set gives the ordinary loop signal when the set-is removed from the switch hook. When a member of the public opens door D2, the. withdrawal of pin P1 releases mechanism CM which sends a ground over one wire of the line to signal the central station as described in the prior Specification. The mechanism CM shown separately in Fig. 4 is similar to a dial transmitter without the impulse mechanism and is set by the operation of pin P1 on a slider OM when the door D2 is closed by a spring closer DC. The slider is geared to the shaft of the mechanism CM. The parts are shown in Fig. 4 in the position they take up when the door is opened. A push rod R controlled by a cam on OM moves downwards and permits a tilting mercury switch MT to close the lamp circuit over leads E1, E2. The contact mechanism consists of springs AC1, AC2 which make the line circuit when the rotary arm A takes up .the position shown, and the cam plate CP which during a portion of its rotary movement makes contact at 2, 3 for sending the ground signal. A slipping plate SP performing a small rotary movement between stops ST1, ST2 prevents operation of springs 2, 3 during the setting movement of CP. The relay MR, Fig. 2, corresponds to the call relay described in the prior Specification and flashes the lamp or gives an audible alarm. The lamp and gong may be detachable from the pillar so that they can be mounted in any convenient position. Loud-speaking set for public use. A microphone M is mounted within or in front of the cone of the loud-speaker LS and both are protected by a grid G. Priority calls. A differential relay at the central station is operated by the ground signal sent by public calls and gives a priority signal to the operator.