Fig. 14
The Buzzer.
The buzzer is the mechanism of a vibrating bell less the hammer and gong. As the armature vibrates it makes a buzzing noise which does not carry as far as the sound from a struck gong. It is used chiefly for a desk call and in telephone exchange work, or any place where general attention is not desired to the signal.
Operating Bells at a Distance.
When it is desired to ring a bell situated at a considerable distance from the push, the resistance of the line becomes objectionable.
Fig. 15
On lines of 500 feet, No. 18 copper wire and upwards, the battery necessary would be very large, two small batteries and a relay would prove more satisfactory.
In [Fig. 15] the circuit of a simple form of relay is given. An adjustable contact screw C is placed where an extension S of the armature A can strike it. This extension is provided with a platinum contact. The connections are as in the figure.
When the push P is depressed, the current from the main battery M energizes the electromagnet E, and the armature A being attracted, contacts S and C meet. These contacts close the second circuit containing the bell B and the local battery L.