Fig. 67
The convenience of having telephone connection in the house or hotel and its advantages over speaking tubes are too well known to need extended comment. Where electric bells have already been installed it is quite feasible now to use the same wires for telephones also.
Telephone sets especially designed for this service are manufactured by the Western Electric Company in their interphone series. They are simple and compact, and may be installed by anyone who can put up an electric bell.
Fire Alarm Circuits.
A fire alarm circuit suitable for factories, private plants or groups of buildings is shown in [Fig. 68]. It is a series system, with closed circuit, the gongs sounding whenever the circuit is opened whether by the contact breaker in the boxes or by the accidental breaking of a wire. This insures that it remains in good working order, as when any part of the circuit is opened, a warning tap is sounded on every bell or gong.
The boxes have contact breakers which send a separate number of impulses for each box, thus announcing the box number on each gong. The boxes and gongs may be located anywhere, as the system is perfectly flexible.
The reference letters in the diagram are as follows: C indicates the gongs which are preferably of the electro-mechanical type, a coiled spring providing force for the blow, electricity being merely used to release and retain the hammer or striker. The alarm boxes are marked BB and the battery which is of the closed circuit type is marked D.
Fig. 68