or Intermittent Electro-motive Force.
Year: 1887

page_text: or Intermittent Electro-motive Force.
We, ROBERT DICK, Manufacturer, and RANKIN KENNEDY, Electrical Engineer
both of the Electric Lamp Works, 115 Woodside Road, Glasgow, Lanarkshire, do
hereby declare the nature of our said invention, and in what manner the same is to be
performed to be particularly described and ascertained in and by the following state-
iment in writing, that is to say :-
In using alternating currents for the distribution of electric energy it is necessary
to measure accurately the forces at work in the system of dynamos, transformers,
main wires and lamps. Very delicate and costly apparatus is at present used for this
purpose in the laboratory, consisting usually of electrostatic instruments requiring
great care and skill in handling and applying them.
By our invention we provide an entirely new and simple method of measurement
which will enable any ordinary engineer to measure alternating or intermittent electro-
motive forces ranging from 0.1 to 10,000 or more volts of potential, and that with
any of the common well known voltmeters or potentiometers now in use for measuring
alternating electro-motive forces of ordinary potentials such as Cardew's voltmeter.
According to our invention we employ any ordinary form of alternating current
transformer, and when the alternating or intermittent electro-motive forces are of
high potential we use the transformer to reduce the pressure or potential to bring it
within the range of the ordinary voltmeter, and knowing the ratio of the reduction,
the reading of the voltmeter has only to be multiplied by this ratio to give the exact
measure of the potential. On the other hand when the potential of the alternating or
intermittent electro-motive forces is too low for accurate measurement by the ordinary
volimeter we employ a transformer to raise the potential to come within the range of
the voltmeter, and divide the reading of the voltmeter by the ratio of increase of
potential in the transformer. The ratio of any transformer depends only on the
number of turns of wire in the primary and secondary conductors with which every
alternating current transformer is wound. Thus if a transformer has one circuit
wound with 100 turns of wire and the other circuit wound with 10 turns of wire, then

page_text: a potential of 1,000 volts acting on the hundred turns, would produce 100 volts poten-
tial at the ends of the 10 turns of the other circuit; and conversely a potential
of 1 volt acting on the circuit of 10 turns of wire would produce 10 volts at the ends
of the circuit of 100 turns, the ratio of such a transformer would thus be as 1 is to 10,
and a voltmeter which could measure between 10 volts and 100 volts could in this way
be employed to measure any potential between 1 volt and 1000 volts.
By a further improvement of our invention one or both of the circuits in the trans-
former is subdivided into sections, so that by making contact with the terminals and
joining two or more sections together we can obtain any ratio of potential in the
transformer which we may desire. Thus a transformer may have 1,000 turns in one
circuit and 100 turns in the other circuit, the 100 turn circuit may be divided into
two halves and the ends brought out for connection, and one of the halves may be
divided again and the ends brought out also and thus we could employ 25 turns, 50 turns
or 100 turns and thereby get a ratio of 40 to 1, 20 to 1, and 10 to 1, respectively from
this one transformer. We connect the whole 1000 turns of one circuit to the potential
to be measured, if it is too high for the ordinary voltmeter, and we then connect the
100 turns to the voltmeter or the 50 turns or the 25 turns as the case may require, if
the potential must be brought down 40 times, we use the 25 turns if it be brought
down only 10 times we use the 100 turns. Conversely if the potential to be measured
is too low for the voltmeter we connect it to the 25, 50, or 100 turns, using the 25 if
we must raise the potential 40 times and using the 100 turns if only 10 times is
required. Any other ratios may be used in the transformer, but the above ratios are
generally sufficient for ordinary practice as by these and a voltmeter to measure
between 10 and 100 volts, potentials ranging from 0.25 to 4000 volts could be
accurately measured. As already stated, any voltmeter suitable for measuring
alternating or intermittent electro-motive forces may be used with the transformers.
Having now particularly described and ascertained the nature of our said Invention,
and in what manner the same is to be performed, we declare that what we claim is :-
First. In a system of distribution of electric energy the combination of an alternat
ing or intermittent current transformer with a voltmeter or potentiometer, for the
purpose of measuring the electro-motive forces or potentials of alternating or inter-
inittent electric currents substantially as herein set forth.
Second. The combination of a transformer of alternating currents with a voltmeter
or instrument for measuring electric potentials for the purpose of accurate measure-
ment of electro-motive forces or potentials which are too small or too great in
magnitude for measurement by ordinary voltmeters or potentiometers.
Third. In a system of distribution of electric energy the combination of a trans-
former of alternating or intermittent currents having one or both of its electric
circuits subdivided to obtain higher or lower ratios between the circuits, with a volt-
meter or potentiometer for the purpose of measuring alternating or intermittent
electro-motive forces or potentials, substantially as herein set forth.