Introduction
Page
Introduction. The principle of an electric bell.[ix]
Chapter I
The Leclanche cell—Polarization—Setting tip—The dry cell—The gravity cell—Connecting up cells[1]
Chapter II
The single stroke bell—The shunt bell—The differential bell—The continuous ring bell—The waterproof bell—Forms of gongs—The buzzer—Long distance bells—The relay—The push—Three point or double contact push—Floor push—Door pull—Indicating push[9]
Chapter III
Bell wires—Joints—Running wires—How to put up a door bell—Combinations of bells, pushes and batteries—Faults in bells, faults in wiring—How to locate and remedy faults[23]
Chapter IV
Fire alarms—Thermostats—Metallic thermostats—Mercury thermostat—How to connect thermostats—Water level indicators—Burglar alarms—Open and closed circuit alarms—Window, door and shade springs—Alarm matting—Yale lock alarm—Door trip alarm[40]
Chapter V
The annunciator drop—The needle or arrow drop—The pendulum drop—Wiring up annunciators—Return or fire call systems—Double wire system—Western Electric single wire system[55]
Chapter VI
Three-wire return call system—Installing elevator annunciators—Burglar alarm annunciators—Clock alarm circuit—Bells for high voltages—Bell-ringing transformers—Combination bell, door opener and telephone circuits—Fire alarm circuit—Interior fire alarm system—Fire alarm system for considerable areas[64]

LIST OF ILLUSTRATIONS

Fig. Page
1Electric bell, push, and battery[x]
2Leclanche cell[1]
3Dry cell[4]
4Gravity cell[5]
5Vibrating bell[10]
6Single stroke bell[10]
7Shunt or short circuit bell[10]
8Continuous ring bell[13]
9Waterproof bell[14]
10Dome gong[15]
11Tea gong[15]
12Cow gong[15]
13Sleigh bell gong[15]
14Spiral gong[15]
15Relay and circuit[16]
16Door push[19]
17Pear push[19]
18Door push[19]
19Wall push[19]
20Floor push[20]
21Door pull attachment[22]
22Wire joint first operation[25]
23Wire joint second operation[25]
24Wire joint insulating[25]
25Section of house showing wiring[29]
26Bell with ground return[30]
27Pushes in multiple[31]
28Bells in series[31]
29Bells in multiple[31]
30Two bells and two pushes[32]
31Two bells and two pushes[32]
32Two bells, two pushes and one battery[33]
33Double contact push[33]
34Grounded bell[34]
35Tongue test of wiring[38]
36Knife test of wiring[38]
37Knife test of wiring[39]
38Metallic thermostat[40]
39Mercury thermostat[41]
40Mercury thermostat circuit[42]
41Water level alarm[44]
42Lever water level alarm[45]
43High or low water level alarm[45]
44Window spring for burglar alarm[47]
45Burglar alarm—closed circuit[47]
46Special bell connection for burglar alarm[48]
47Special bell connection for burglar alarm[49]
48Burglar alarm and relay[50]
49Window-shade contact spring[51]
50House wired for burglar alarm[52]
51Door trip alarm[53]
52Annunciator drop[55]
53Needle drop[56]
54Needle drop indicating[56]
55Pendulum drop[57]
56Annunciator drop circuit[58]
57Simple annunciator circuit[59]
58Annunciator and fire call circuit[60]
59Single-wire room and fire call[61]
60Three-wire return call circuit[65]
61Elevator bells and annunciator circuit[67]
62Burglar alarm annunciator circuit[69]
63Clock alarm circuit[71]
64Bell-ringing transformer[73]
65Bell-ringing transformer with three secondary voltages[73]
66Western Electric interphone system[75]
67Western Electric interphone system for more extensive service[77]
68Fire alarm circuit[79]
69Interior fire alarm circuit[81]
70Fire alarm circuit for considerable areas[82]

INTRODUCTION

An electric bell depends for its action on the fact that a piece of iron wound with insulated wire becomes a magnet and will attract another piece of iron just so long as an electric current is allowed to travel through the wire.

The instant the current ceases, the magnetism also ceases, and the attracted piece of iron (termed the armature) is no longer held in contact.

The general construction of an electric bell is shown in [Fig. 1]. M M are coils of insulated wire wound on soft iron cores. A is a soft iron armature mounted on a flat spring so that it is normally kept a slight distance away from the soft iron cores. S is a brass screw with a platinum tip touching a platinum disc on a spring attached to the armature.

When the push button P is pressed down, its two brass springs touch each other, the current from the battery cell B then flows through the wire W, through the push P, through the coils M M, along A to the platinum disc, out at S, which touches this disc, and back to the battery.