Bauhaus-Universität Weimar

Optic Projection: Principles, Installation and Use of the Magic Lantern, Projection Microscope, Reflecting Lantern, Moving Picture Machine
Gage, Henry Simon and Henry Phelps Gage
Ch. XIII] 
If the wattmeter were wrongly connected, the instrument could 
not register the watts on the one hand and on the other it might be 
Fig. 256 
the Power Delivered by the 
G Dynamo. 
W Wattmeter. 
A Arc lamp. 
§ 670. Portable wattmeter.—This has a pointer which shows 
directly in watts, the power consumed at a given instant. 
§ 671. Stationary or house 
wattmeter.—The wattmeter for 
the electric supply looks some¬ 
thing like a gas meter for the gas 
supply. It is of the integrat- 
Wattmeter to Measure O pe, is permanently con¬ 
nected with the line, and con¬ 
tains a wheel, the speed of whose 
rotation is directly proportional 
„ to the power consumed. This 
R Rheostat. . 
The fine wire connects the watt- wheel turns pointers over the 
meter with the line where the power is dials on which are indicated 
to be measured. kilowatt-hours. The numbers 
toward which the pointers are directed indicate the kilowatt- 
hours which have been used, just as the pointers in a gas meter 
indicate the number of cubic feet of gas which have been used. 
For example, by consulting the wattmeter before and after an 
exhibition one can see how much work, measured in kilowatt-hours 
has been consumed by the arc light. 
Suppose the voltage of the line were no, and the voltage between 
the carbons is 55 volts. Suppose the amperage is 20, then the 
watts should be (volts times amperes) 55x20 = 1100 watts at any 
instant, and for an hour, for example, it would be 1100 watt hours, 
or 1.100 kilowatt-hours. 
§ 671a. With both direct and alternating current, when a rheostat is in 
the circuit, the amperage may be found by the aid of the stationary’ wattmeter, 
this is always present in a house supply of electricity, as is the gas meter for the 
gas supply, and one does not always possess an ammeter. 
It is necessary to know the voltage of the line. This is usually no or 220. 
One must also know the watts, or kilowatts at any given instant. This can 
be found by the wattmeter as follows: Suppose the reading is 1.87 kilowatt- 
hours. As this number was obtained by multiplying volts x amperes x time, 
and the time is one hour, then the kilowatts of power consumed is 1.87. The


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