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Circuits

bell, bells, push, ring, fig, rung and shown

CIRCUITS.

The possible combinations of the various parts into complete circuits are so varied that it would be impossible to describe them all; in fact, almost every one is to a certain extent a special problem. It is, however, possible to give typical circuits the underlying principles of which can be applied successfully to particular case.

Fig. 11 shows a bell circuit in its simplest form, in which P represents the push, B the bell, and C the battery; all connected in series. The circuit is normally open at P, and hence no cur rent flows to exhaust the batteries.

When P is pressed, the circuit, otherwise complete, is closed and current passes through the bell causing it to ring, as already ex plained. For instance, the push might be located beside the front door, the bell in the kitchen and the battery in the cellar; the location depending on the results desired and conditions to be met. The wire between P and C may, if necessary, be dispensed with and connection made to ground at G and G, as shown by the dotted lines.

Fig. 12 shows an arrangement by means of which one bell B may be controlled by either of the pushes P or P'. This system may be extended to any number of pushes similarly connected.

A method for ringing two bells simultaneously from one push is shown in Fig. 13, where both bells B and B' will ring from push P. Bells, if connected in this manner, should have as nearly as _ possible the same resistance, otherwise the bell of lower resistance will take so much current that there will not be a sufficient amount left for the other. Also, the batteries must be of greater current capacity as the amount of current taken is, of course, doubled. This system can be extended to any number of bells connected in this way, up to the limit of capacity of the battery to ring them. Figs.

12 and 13 may be combined so that two or more bells may be rung from any one of two or more pushes.

In Fig. 14 is shown a scheme for ringing either bell, B or B', from one push and one battery by means of the two-point switch S. When the arm of the switch is on contact 1, the push will ring bell B, and when on contact 2 it will ring bell B'.

In Fig. 15 is shown a method of connecting bells in series so that B and B' may be rung from P. If all the bells so connected

were of the vibrating type, they would not work satisfactorily, as it would be impossible to time them so that the vibrations would keep step, hence only one bell should be of the vibrating type, and the others should have the circuit breakers short circuited, the vibrating bell serving as interrupter for the whole series. Obvi ously this system requires a higher volt age than parallel connection, and the cells must be of sufficient E.M.F. to ring the bells satisfactorily. Several bells may be connected in this way, if desired, up to the limit of voltage of the battery.

Oftentimes a bell is to be rung from several different places. For instance, the bell in an elevator may be rung from any one of several floors, or the bell in the office of a hotel may be rung from any one of several different rooms. In this case it is necessary to have some device to indicate from which push the bell was rung. The annunciator furnishes this information very well. A three station annunciator is shown in Fig. 1(i. The connections for an annunciator are shown in Fig. 17 where A. represents the anun ciator, B the bell, C th3 battery, and P', P', and P' the pushes. I-or instance, when P' is pressed, the current passes through the electromagnet controlling point 1 on the annunciator which causes the arrow to be turned and at the same time the bell rings. After the attendant has noted the signal, the arrow is restored to its nu mal position by pressing a lever on the bottom of the annun ciator box.

The electric burglar alarm furnishes a very efficient protec tion and is an application of the principles already described. The circuit, instead of beiiig completed by a push, is completed by contacts placed on the doors or windows so that the opening of either will cause the bell to ring. The same device may be used on money-drawers, safes, etc.

In the case of the electric fire alarm, the signal may be given either automatically when the temperature reaches a certain degree, or pushes may be placed in convenient locations to be operated manually. The pushes should be protected by glass so that they will not be tampered with, it being necessary to break the glass to give the alarm.