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pointer. The small battery tester which is very simple in construction works on exactly the same principle, except that the vertical plunger which is drawn into the solenoid has the scale indicated upon it. The solenoid is kept pressed out against a stop by spring pressure which is overcome as soon as the current passes through the winding. The plunger type is not reliable for very small readings and is readily affected by any magnetic field in the vicinity.
The instrument shown at E is a magnetic vane type. In this a vane of soft iron is supported eccentrically or off center and when a current passes through the surrounding coil the
AMPERES vane is attracted toward the position where it will conduct the greatest number of lines of force,
GRAY A DAVIS this movement actuates the pointer attached to the vane support and a hair spring is used as in other instruments to return the pointer to zero when the current flow ceases and also to steady Fig. 23.-Typical Dash Type Amperemeter the action of the instru
Used with Modern Lighting System. ment. The small amperemeters are used only for testing dry cells, as the scale reads only to 30 amperes. This form of instrument is also used as an indicator to show the rate of charge of a storage battery by the generator or current consumption of the lamps of the lighting system. The ordinary form of ammeter should never be used for testing storage cells and a voltmeter is necessary for this purpose. Sometimes an amperemeter is so constructed with an internal resistance that can be put in series with the solenoid coil that it will read voltage on another scale. An instrument thaf
POSITIVE, SOMETIMES ABBREVIATED "P"
ARROW INDICATES DIRECTION OF CURRENT FLOW.
PUSH BUTTON OR
LIGHTING SWITCH, ♡ VOLTMETER. - STARTING SWITCH. SHUNT WOUND MACHINE
MOTOR-GENERATOR MOTOR OR GENERATOR.
3-TERMINAL, SERIES WOUND MACHINE
MOTOR-GENERATOR MOTOR OR GENERATOR.
4-TERMINAL, G GENERATOR,
с CARBON OF DRY BATTERY. M MOTOR.
Z ZINC OF DRY BATTERY.
DRY CELLS OR STORAGE BATTERY. CELLS IN SERIES.
AMPERE, UNIT OF CURRENT QUANTITY.
IN ONE DIRECTION.
THEN THE OTHER.
Fig. 24.-Index to Signs, Symbols and Abbreviations Used in Wiring
will indicate 30 amperes and register up to eight volts has a range that is ample for all practical purposes. Some very low reading ammeters were formerly sold extensively as coil current consumption indicators, but with the passing of the vibrator coil ignition system they are no longer used to any extent.
BATTERY AND COIL IGNITION METHODS
How Compressed Gas May Be Ignited—Methods of Electric Ignition-Parts
of Simple Ignition System-Induction Coil Action—Timers and Distributors—Spark Plugs—Individual Coil System-Vibrator-Distributor Systems-Master Vibrator Systems-Non-Vibrator Distributor System-Low Tension Ignition-Double and Triple Ignition Systems—Battery Ignition System Troubles—Charging Storage Batteries—Care and Repair of Spark Plug Faults—Induction Coil—Timers—Wiring Troubles and Electro-static Effecis-Timing Battery Ignition System.
How Compressed Gas May Be Ignited.—One of the most important auxiliary groups of the gasoline engine comprising the automobile power plant and one absolutely necessary to insure engine action is the ignition system or the method employed of kindling the compressed gas in the cylinder to produce an explosion and useful power. The ignition system has been fully as well developed as other parts of the automobile, and at the present time practically all ignition systems follow principles which have become standard through wide acceptance.
During the early stages of development of the automobile various methods of exploding the charge of combustible gas in the cylinder were employed. On some of the earliest engines a flame burned close to the cylinder head and at the proper time for ignition, a slide or valve moved to provide an opening which permitted the flame to ignite the gas back of the piston. This system was practical only in the primitive form of gas engines in which the charge was not compressed before ignition. Later, when it was found desirable to compress the gas a certain degree before exploding it, an incandescent platinum tube in the combustion chamber, which was kept in a heated condition by a flame burning in it, exploded the gas. The naked flame was not suitable in this appli
cation because when the slide was opened to provide communication between the flame and the gas the compressed charge escaped from the cylinder with enough pressure to blow out the flame at times and thus cause irregular ignition. When the flame was housed in a platinum tube it was protected from the direct action of the gas, and as long as the tube was maintained at the proper point of incandescence regular ignition was obtained.
Some engineers utilized the property of gases firing themselves if compressed to a sufficient degree, while others depended upon the heat stored in the cylinder head to fire the highly compressed gas. None of these methods were practical in their application to motor car engines because they did not permit flexible engine action which is so desirable. At the present time, electrical ignition systems in which the compressed gas is exploded by the heating value of the minute electric arc or spark in the cylinder are standard, and the general practice seems to be toward the use of mechanical producers of electricity rather than chemical batteries used alone.
Methods of Electrical Ignition.--Two general forms of electrical ignition systems may be used, the most popular being that in which a current of electricity under high tension is made to leap a gap or air space between the points of the sparking plug screwed into the cylinder. The other form, which has been almost entirely abandoned in automobile practice, but which is still used to some extent on marine engines, is called the low-tension system because current of low voltage is used and the spark is produced by moving electrodes in the combustion chamber.
The essential elements of any electrical ignition system, either high or low tension, are: First, a simple and practical method of current production ; second, suitable timing apparatus to cause the spark to occur at the right point in the cycle of engine action ; third, suitable wiring and other apparatus to convey the current produced by the generator to the sparking member in the cylinder.
The various appliances necessary to secure prompt ignition of the compressed gases should be described in some detail because of the importance of the ignition system. It is patent that the scope of a work of this character does not permit one to go fully into the theory and principles of operation of all appliances which