The Donaldsonville chief. [volume] (Donaldsonville, La.) 1871-current, 1911-02-11
How Electricity is Measured.

| =
# Few Of us. outside of engineering g
cles, know how that mysterious serva,
electricity, is measured. We onIv knt
tnat the regular monthly bill calls /
1567-l543-24 kw-hr. for which nIea
remit 81, 30" Many of us have gone dow
cellar, or up in the attic, with q liehtf
candle to stare with mystifed wonder Ar
profound awe at the little mechanic
meter with its incomprehensible dials an
unreadable figures. only to wonder what
is all about.
The fact is that electricity, Of strictl
speaking, electric energy, is measured i
kllowatt hours. A kilowatt hour is prae
tlcally the same as one and one-thir
horsepower hours, since 746 watts eous
one horsepower. The watt is d rate q
work Just as horse power is rate o
work. One tells how hard the dynam
mas to work, while the other tells hoy
hard horse OF engine has to work t,
produce the required energy.
Ihe 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 meter The MOVING
part OF the motor, Or armature, is connect.
ed 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 cleo
tricity. A thousand watt hours is called
kilowatt-hour. The prefix .kilo'' all
ways means 1000 A kifowatt- hour costs
about 20 cents. If the result is desired
IN n<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 instru-
nent which measures the quantity Of
electricity or Juice is known as an am
meter, because quantity of electricity is
always measured in amperes. An instru
nent which measures the pressure which
1rlves the electricity is called voltmeter,
since electric pressure Is measured in volts
ust as water pressure is measured in
pounds. The Wattmeter, however, takes
account of both pressure and quantity;
hat is. it multiplies the volts by the am
oeres and gives the result in watts. Volts
multiplied by amperes give watts, just .as
'ounds-times-feet give horsepower pro-
'ided we assume that the work was done
n certain time-thae Is. SO much work
lone IN a second, or minute, or hour,
The dynamo or generator" furnishes ed
certain quantity of energy in kilowatts.
,ut this amount of energy must be used
or one hour before one kilowatt-hour can
'e charged. Two kilowatts for half an
lour would amount to the same thing.
.hus it is necessary not only to state the
ate OF work in kilowatts, but also to state
he time in hours, hence the hils. states
hat the cost has been SO #ach for such
ind such kiloWatt- -haAss-that is. So manv
ilowatts furnished light or power for so
n any hours. For example, 10000 watts
mercy supplied for fve hours would
mount to 5O,QQ0 Watthours or fifty kilo-
yatt- hours.
The ordinary sixteen eandle-po lamp
Onsumes energy at the rate of about
ltty-five watts, since the pressure exertea
y the generator is about 10 volts. and
ach lamp allows one-haH of an annpere
0 flow through it. This is three and one
alt watts to caNass power. Mazda
amps use about ONE and one-haf watts
. can.aa.y.neMer, One hundred and ten
& s.si,aasslphea BY q half gives ffty-five, the
lumber luqtmq9 of watts, OF, as the engineer often
avs. sjoules per second. The ioule is,
trictly. certain amount of energy or
york exactly like the ordinary foot pound.
nd is related to the watt in the. sanle
,ay the foot pound is related to the horse
over, differing only in stating the time
:. which certain work is done It makes
big difference whether work is done in
n houE or q week, and of course we wish
d pay for work actually performed This
he Wattmeter really keeps track Of, and
,hether we use one light Or q hundred
his little instrument will always be on
and, night and day, TO take record of
he amount used. Perhaps the unthink-
lg person who carelessly leaves the elee~
sie light on when not needed would be |
lore careful if he remembers that the
enerator has to actually exert one-four-
zenith of horse power to keep that |
lngle light goins, even though the cost Is
ut cent an hour,