|P.O. ENGINEERING DEPT.
Issue 1, 1933
POLICE TELEPHONE AND SIGNAL SYSTEM
A call point may take the form .of a street pillar, police kiosk, or sub-station equipment.
STREET PILLAR AND POLICE KIOSK CALL POINTS
A specially-designed telephone is installed at these points, from which dual telephone facilities are provided, i.e.
- By loud-speaking telephone available to. the public upon simply holding open a door, which is self-closing but
- By means of a microtelephone available only to the police, or other authorized persons in possession of a key.
3. Public Call Door
The loud speaker and transmitter, for public use, are located behind a protective grille, and require no handling by the caller. It is only necessary for the public to pull and hold the door open, and thereafter to speak in a normal manner in the direction of the
grille. The answering voice of the police operator can be clearly heard, as a valve amplifier at the Police Station is used in this circuit. The arrangement is, amplified speech from the operator to the public call point, and normal speech from the public call point to the operator.
4. Public Call Door Pin
An adjustable projecting pin is fitted on the inside of the public call door. When the door is closed, this pin projects through an aperture beside the grille and presses a
plunger, which keeps an impulse machine in a wound position. The act of opening a public call door releases the impulse machine, which then causes the lines to be connected for
5. Public Call Door Check
The door, when released at the termination of a call, is made to close slowly by the action of an oil
compression door check.
6. Mounting for Unit, Telephone P.A. No. 1
This mounting base is provided for the termination of the permanent connexions at pillars and police kiosks.
Mounted upon it are the fuses for the local power supply for lighting the signal lamp, and in the power circuit is also fitted a double-pole push switch, which is kept in an operated position by an indentation in the outer cover so long as the cover is on. The object of this arrangement is to automatically cut off the power supply whenever the outer cover of the telephone unit is removed.
7. The lines, the earth to the instrument, and also the power leads, are
terminated on a special 5-point jack mounted on the base, and these connexions from the telephone unit are
similarly connected to a 5-point plug. A runner is also provided on the mounting base so that the plug on the telephone unit can be jacked-in to the connexions on the base, and the telephone unit is kept in position by means of two screws.
8. Bracket P.A. No. 1
In the case of pillars, the mounting base is fitted direct on the pillar. The public call door and protecting
grille form part of the pillar head, and the telephone unit, when jacked-in on the mounting base, fits close to the protecting
grille. When the apparatus is fitted in a police kiosk, however, it is necessary to support the mounting base to the public call door and the
grille structure, which are in one unit, by means of a special bracket known as “Bracket P.A. No. 1.” The whole assembly is then fixed in a suitably-constructed aperture in the police kiosk by means of metal corner cross-pieces, bolted into bosses provided on the back of the grille structure.
9. Unit, Telephone P.A. No. 1 and No. 2
In a party-line there are three stations, the first (or A station) and the second (or B station) being termed side
stations. The third (or last station) on the line is called the Terminal station.
10. Each party-line is capable of serving a maximum of three call points with full selective
signalling. Up to two additional stations may be provided, if required, and these must be connected to either, or both, of the side stations. The additional stations
will be signalled at the same time as the side stations to which they are connected.
11. On each telephone unit a terminal board is fitted, to enable the unit to be connected as for an A, B, or Terminal station. In the case of a terminal station, however, an additional polarized relay is required, through which the line circuit is completed for the continuous-test facility, and, for this case, “Unit, Telephone P.A. No. 1“ is provided. “Unit, Telephone
P.A. 2“ can be used as either an A or B side station, by suitably arranging the straps on the terminal board. This board is clearly visible in
picture below of the Unit, telephone, PA No. 1, which shows the unit employed at a terminal station.
12. The base of the loud speaker cone is fixed in a metal ring which fits closely against the back of the protecting grille, and the microtelephone is fixed in the inside of
13. Impulse Machine
This is contained in a metal case, and is kept in a wound condition by the pin in the public call door, so long as the door is closed. The opening of the door releases the impulse mechanism which causes a fleeting earth of 200
milli-seconds duration to be put on the A-wire on one set of springs, to commence the operation of a relay in the
unit at the switchboard. While another set of springs closes a contact in each wire of the line, to connect
the microtelephone and loud speaker to the line.
14. A mercury-tube contact fitted over the impulse machine is mechanically closed with the operation of the impulse machine, and causes the lamp on the top of the telephone
unit, when fitted in a police kiosk, and also the internal light, if fitted, to glow steadily while the public call door is open. Should this facility. not be required, in any special circumstances, the mercury-tube contact may be disconnected at the terminals provided.
15. An impulsing relay provided with a mercury contact is fitted for the purpose of transmitting the ringing impulses from the line, by means of the mercury-tube contact and the power circuit, to the signal light at one second intervals.
16. A Telephone No. 164 is provided for police calls, and this is kept in a special compartment under lock and key, in the case of pillars. Where a police kiosk is used, the “Telephone No. 164” is inside the kiosk, which itself is locked. There is no public access to the police portion of the street call point equipment. The police officer calls the switchboard by simply removing the telephone from the gravity switch, which causes two contacts in the latter to change over the line from the signal portion of the circuit to the microtelephone for police calls.
17. This consists of a “Telephone No. 196 C.B.” and a “Bell Set No. 22,” where this equipment is fitted on a party line as a side station.
It may be found, however, that the local requirements of Fire Station Authorities demand a separate party line for the Fire Station, in which case the equipment would be connected as a terminal station, and it is then necessary to add
a ”Relay No. 309 B“ with a 2,000 ohm resistance and a “Bell No. 56C“ to preserve the
continuous test facility.
18. The “Telephone No. 196 C.B.” will be fitted on a “Bracket No. 12” when required for wall fixing.
19.An extension bell can also be fitted, either as a continuous, or non-continuous arrangement.