fig. 706. Public Telephone Kiosk
fig. 707 Venner Time Switch (cover removed)
fig. 708 Venner Solar Dial
Kiosks. Public call office telephones are usually housed in a small kiosk easily accessible from the public highway. The kiosks are of four types, the No.2 type being illustrated in Fig. 706. The largest size is the No.4 type, and at the rear of this kiosk is a stamp-vending machine and a letter-posting box. The No.3 kiosk is constructed from pre-cast concrete sections. The kiosks are usually lighted from the public electricity supply mains, and the lighting is controlled by a time switch or a selenium cell. In erecting kiosks, it is necessary to ensure a satisfactory earth connexion for the emergency-calling circuit, and an earth plate is buried adjacent to the site of the kiosk.
A typical time switch is illustrated in Fig. 707. It is a spring-driven, electrically-wound, single-pole, 1 amp. switch fitted with a solar dial, and switches the lamp on at dusk and off at dawn. The clock winds itself every eight hours by means of a small electric motor. To guard against stoppage due to failure of the power supply, the clock is provided with three days' spring storage and, should such a failure occur, the clock winds itself fully immediately the supply is resumed, irrespective of the duration of the failure. The solar dial (Fig. 708) is a device that automatically follows the rising and setting of the sun, day by day, and alters the position of the operating hands of the time switch accordingly. For the British Isles, ten different types of solar dial are provided to cater for the variations in solar time.
Two fuses are incorporated in the box to protect the whole of the electrical system. A special hand switch, which remains on only so long as it is held in position, is provided for lamp testing.
In later patterns of these time switches, the containing box has an inspection window in the lid to enable the clock time to be checked by means of a fixed pointer, marked "Time," and the markings on the revolving dial.
The only disadvantage of a time switch is that, should the natural light fail during the day period, due, say, to fog, the light of the kiosk is not switched on. To overcome this disadvantage, a control circuit embodying a selenium cell has been devised. With this arrangement, the illumination is provided whenever the state of the light warrants, and, when the light improves, the lamp is extinguished.
fig. 707 Venner Time Switch (cover removed)
fig. 708 Venner Solar Dial