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26
INTERNATIONAL PROJECTIONIST
June 1933
SUPER INTENSITY
AUTOMATIC PROJECTION LAMP
H. C. 10
Super Intensity Lamp
Tk
Lamp With Accurate Arc Regulation
and Arc Focusing by Means of
the Heat From the Arc Itself
H. C 10 Features:
• Self-Starting • Self-Focusing
• Independent Negative Feed Regulation
• Magnetic Stabilization • Better Arc
• Self-Lubricating Bearings
• Standard Ammeter • Carbon Indicator • Forced Air Cooling • Correctly Shaped Hood
• No Feed Rollers • Full 22-inch Trim
Descriptive booklet on request. Write for it to
HALL & CONNOLLY, Inc.
24 Vandam St.
New York, N. Y.
circuit of a motor, the motor can be made to "speed up," or "slow down," by changing the amount of resistance in the field circuit. See Figure 13. When the resistance of a motor field circuit is decreased, the motor "slows down" and if the resistance is increased, the motor will "speed up." Therefore, the use of a variable resistance in the field circuit is a very practical method of controlling the speed of a DC motor.
Ratings
Motors are rated in horsepower (hp.) or kilowatts (kw.). One horsepower is equal to approximately threequarters of a kilowatt.
A kilowatt is a thousand watts, and a watt is a unit of electric power. The number of watts of power in a DC electric circuit, or in an AC circuit of pure resistance, is equal to the product of the voltage across the circuit and the amperes through the circuit.
DC generators are usually rated in kilowatts.
AC generators and converters are usually rated in kilovolt-amperes (kva). The kv-a of a circuit is the product of the volts and amperes divided by 1,000. For example: An AC ma:^ chine that will deliver 20 amperes at 440 volts has a rating of 20 multiplied by 440 and divided by 1,000, or 8.8 kv-a. In DC circuits or in AC circuits of pure resistance the KV-a. and kw. are the same, but in some AC circuits this condition does not hold, and the product of the voltage and current is not equal to the watts of power delivered to, or taken from, the circuit. In all such cases, the product of volts and amperes is always greater than the watts of power. The reason for this is very complicated and will not be taken up here.
Heat is Limiting Factor Usually motors and converting equipment are rated also in volts and in amperes. The rating in amperes should never be exceeded, even though the machine may not be delivering its rating in horse-power or kilowatts, because the heating (which is the limiting factor) depends upon the current through the machine.
(To be continued)
RECTOX BATTERY CHARGERS
The Rectox Battery Charger is completely described and illustrated in a recent four-page publication issued by the Westinghouse Elec. and Mfg. Co. The construction, application, and operation of the charger are explained in the leaflet pointing out the distinctive features and advantages of this type of dry, non-chemical, metallic oxide rectifier. Copies of the leaflet may be obtained from the nearest district office or direct from the company at East Pittsburgh, Penna.