ERICSSON BULLETIN No. 6  PAGE No. 31


Police Telephone System
Further Developments

Modern methods of communication and transport have occasioned considerable change in police organisation and control.

Hitherto, with the method of control generally used, the police officers reported on duty at a police station, and after the routine and other orders were conveyed to them they proceeded to their beats. Supervision was maintained by periodic visits to the beats by sergeants and inspectors. Close contact with headquarters was not possible once an officer was on his beat. This form of control is being largely superseded by one in which use is made of police boxes and pillars erected in the streets and telephonically connected to headquarters. Each police box becomes, virtually, a police sub-station and personal appearance at headquarters by the beat officers is rarely necessary, contact being maintained via the telephone system. All officers report “on “ and “off” from assigned boxes or pillars, and thereafter, during their period of duty, report, in a scheduled order at definite times, from other boxes or pillars on their beats. Notices and routine reports are posted in the boxes; distribution being made by motor vehicle.

The general desire by the police authorities for a modern telephone communication system has been met by the Ericsson Police Telephone System; adopted as standard by the British Post Office and described in Bulletin No. 2 January 1933, and No. 3 July 1933. This system provides a communication network interconnecting boxes and pillars in the streets, police sub-stations, police headquarters and the Post Office telephone exchanges. Line costs are reduced to a minimum by connecting more than one street point, i.e. box or pillar, to each line. The public are permitted restricted use of the system public calls being limited to communication between the street points and the police or fire stations. Speech from the police operator to the public is received at the street point by way of a loud-speaker.

The police authorities have not hesitated to take full advantage of the facilities offered by the Police Telephone System to remodel their organisation upon modern
lines. The increasing importance of the system in police administration and the tendency of the public to use the services 

offered, even as far as for other than strictly emergency calls, have necessitated further development of the system. The development is concerned, mainly, with the following facilities:-
(a) Inward Signalling
(b) Public Call Preference
(c) Intrusion
(d) Extension of public calls.

Fig 1. Automatic Dial Mechanism Operated by Police handset Fig 2. Automatic Dial Mechanism Operated by Public Door

The first facility is essential for the successful working of the “box“ system of police control, because it indicates, at the switchboard, which of the call points connected to a line is calling and also the class of caller, i.e. police or public.

A signalling device, based upon an automatic telephone dial mechanism, is operated automatically when the police handset is lifted, or the public door is opened, and transmits to the line a train of pulses. The mechanisms are shown in Fig. 1 and Fig 2. These pulses operate relays at the switchboard and light a lamp display to give the required indication. In connection with this facility a considerable amount of circuit development has been carried out to prevent lost calls, and to reduce to a minimum the possibility of false calls. If mutilation of the pulse train should occur due to extreme conditions, occurring but rarely in practice, the type of call is always shown correctly. The answering of a public call is thus never delayed because of an incorrect display.

Delay which may arise from other causes is eliminated by facilities b and c. The former gives preference to a public call display in such a manner that, if a police call is displayed and awaiting attention and a public call should originate on the same line, the display of the police call is cleared and the public call display substituted. A police call following a public call cannot, however, clear down the public call display.

Facility (c) permits a public call, that originates on a line already in use by a police call, to be displayed irrespective of the destination of the police call, which may be extended to a police extension line, another switchboard in the police area or to the Post Office exchange. This facility also permits an intruding police call to be displayed ; in which case facility (b), giving preference to a public call display, will function should a public call originate.

Previously all public calls were answered by the operator who, by actuating certain keys, was connected to the line via an amplifier. Experience has shown that, generally, the operator is fully occupied with routine police calls, and the question of permitting, if necessary, the answering of public calls at some point remote from the switchboard has received consideration. The circuits have been redesigned so that the answering of public calls is effected by special cord circuits, thus allowing extension in a manner similar to that of a police call.

Extension can be made to selected extension lines only; such lines may include those to the charge room, the superintendent’s office, the ambulance and fire-stations. The operator may “listening“ to an extended call ; a facility of great value on fire calls.

The switchboards are each equipped with six of these special cord circuits and, since the answering of a public call requires amplified speech, an amplifier is associated with each cord circuit. The amplifiers are accommodated on the top of the switchboard as seen in Fig. 3, above. The plugs of the public-call cord circuits are situated in the centre of the switchboard and are, therefore, accessible to both operators. Each amplifier employs one valve only, and is fitted with a “suppressor” using metal rectifiers for reducing, to a comfortable level, the strength of that part of the loud speaker’s output which is returned to the operator’s telephone by way of the street point transmitter. Fig. 4, below, shows clearly the compact form of the amplifier and suppressor unit.

The public-call cord circuits are arranged so that an attempt to extend a public call to any line other than those assigned will
cut-off the amplifier and light the alarm lamp. This also occurs under any other condition of misuse or incorrect operation thereby reducing failure, due to the human element, as far as possible.

January 1935

 

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