The Denison review. [volume] (Denison, Iowa) 1867-current, 1911-12-20

O1kElVl O1NvaVl,
ELECTRIC METER
The Electric Meter and How Little
Instrument Tells the Amount
Of Electricity Used.
1T is NOW IN GENERAL USE
|"1567-1543-24 K. W. hr, for Which
Please Remit $2.40"-Then You
Wonder Why and Wherefor.
Few outside of engineering circles
know how that mysterious servant,
electricity, is measured. We only
know. that the regular monthly bill
calls for N1567-1543-24 XIV. mr., for
which please remit $2.4O." Many of us
have gone down cellar or up in the
attic with a lighted candle to stare
with mystified wonder and profound
awe at the little mechanical meter
with it's incomprehensible dials and
unreliable figures, only to wonder
what it was all about. The fact is that
electricity, or strictly speaking, electric
energy, is measured in kiloWatt-hOurs.
A kilowatt-hour is practically the same
as one and one-third horse power
hours since TAG watts equal one horse
power. The watt is rate of work
just as horse power is rate OF
work. One tells how hard the dynamo
has to work, while the other tells how
hard horse or engine has to work to
produce the required energy.
The measurement of electric power
may be simply explained thus: The
current enters the house and certain
fraction passes through small motor
contained in what is called a meter"
The moving part of the motor, or
armature, is connected to an ordinary
counter, such as used on bicycles, gas
meters and automobiles. This system
of toothed wheels is arranged to count
the number of watt hours of electric
ity. A thousand watt hours is called
kilowatt-hour. The prefix "kilo" al
ways means 1000. A kilowatt-hour
costs about ten cents. If the result
is desired in horse power hours, it is
only necessary to remember that
kilowatt-hour is the same as one and
one-third horse power hours.
The wattmeter is peculiar in that
it measures power consumed. An in
strument which measures the quantity
of electricity or Juice" is known as
an ammeter, because quantity Of
electricity" is always measured in
amperes. An instrument which meas
ures the pressure which drives the
electricity is called voltmeter, since
electric pressure is measured in volts
just as water pressure is measured in
pounds. The wattmeter, however,
takes account of both pressure and
quantity; that is, it multiplies the
volts by the amperes and gives the re-
suit in watts. Volts multiplied by am
peres gives watts just as pounds times
feet give horse power, provided we
assume that the work was done in
certain time-that is, so much done in
a second, or minute, or hour. The dy-
namo or generator" furnishes a GER
tain quantity of energy in kilowatts,
but this amount of energy must be
used for one hour before one kilo-
watt-hour can be charged. Two kilo-
watts for half an hour would amount
to the same thing. Thus it is neces-
sary not only to state the rate of
work in kilowatts. but also to state
the time in hours, hence the bill states
that the cost has been so much for
such and such kilowatt-hourS-that is.
so many kilowatts furnished light or
power for so many hours. For ex-
ample, 10000 watts energy supplied
for five hours would amount to $4,000
watt-hours or fifty kilowatt-hours.
The ordinary sixteen candle power
lamp consumes energy at the rate of
about fifty-five watts since the pres
sure exerted by the generator is about
ITO volts, and each lamp allows one
half of an ampere to flow through it.
This is three and One-half watts to
a candle-power. Mazda lamps use
about one and one-half watts to a
candle power. One hundred and ten
multiplied by a half gives fifty-two,
the number of watts, or as the en-
gineer often says, "joules per Sec
ond." The joule is, strictly, certain
amount of energy or work exactly like
the ordinary foot pound. and is related
to the watt in the same way the foot
pound is related to the horse power.
differing only in stating the time in
which a certain work Is done. 1t
makes a big difference whether work
is done in an hour or week, and of
course we wish to pay for work actual
ly performed. This the wattmeter
really keeps track of. and, whether
We use one light or hundred, this
little instrument will always be on
hand. night and day, to take record
OF the amount used. Perhaps the I'M
thinking person who carelessly leaves
the electric light on when not needed
would be more careful if he remem-
bers that the generator has to actual
ly exert One-fourteenth of horse pow
er to keep that single light going, even
though the cost is but half cent an
Herald
NJ,