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482 ELECTRIC MEASUREMENTS [Cn. XIII
For the voltmeter. — After all the connections for the circuit are complete, connect the two terminals of the voltmeter to any two parts of the line between which it is desired to measure the difference of potential.
For the ammeter. — After all the connections for the circuit are complete, and after the arc has been found to work satisfactorily, cut one of the wires and insert the self-containing ammeter in between the two cut ends just as if it were a short piece of heavy wire. If there is an outside shunt connect the ends of the supply wire to the large binding posts of the shunt and the wires of the ammeter to the smaller binding posts of the shunt.
§ 669. The Wattmeter. — This is an instrument for measuring electrical power or activity. There are two types of wattmeter — the portable or indicating wattmeter and the integrating or supply wattmeter. Both work on the same principle, but the method of indication is different.
The wattmeter has two sets of terminals or binding posts. One set is connected with the line in series — along one wire — like an ammeter, while the other set is connected in multiple — that is, to both lead wires — like a voltmeter. In fact this instrument is a
sort of a combination voltmeter and ammeter, as it measures the product of the volts times the amperes.
In connecting the wattmeter FIG. 255. WATTMETER TO MEASURE p.reat care must be taken to ret THE POWER CONSUMED AT THE ARC.
G Dynamo. the sets of binding posts correct
W Wattmeter. ly joined with the line. That is
R Rheostat. the binding posts for the current
The heavy line wire passes to the terminals of the wattmeter must
wattmeter and from it to the upper car be connected in series or along
bon. From the lower carbon the heavy
wire passes to the rheostat and back one Wire like the ammeter (fig. to the dynamo. The fine wire passes 2_3) while the voltage binding from the upper carbon to the wattmeter, and from the wattmeter to the posts must be connected in paralower carbon. With this connection of llel or across the line, like a the wires the power consumed at the arc is measured. voltmeter (fig. 272).