A NEW OR IMPROVED ELECTRIC METER
Year: 1883

page_text: LETTERS PATENT to William McWhirter of 219½, Argyle Street Glasgow in
the County of Lanark, North Britain for an Invention of "A NEW OR
IMPROVED ELECTRIC METER"
PROVISIONAL SPECIFICATION left by the said William MoWhirter at the
Office of the Commissioners of Patents on the 18th July 1883.
2
WILLIAM MCWHIRTER of 2191 Argyle Street Glasgow in the County of Lanark
North Britain "A NEW OR IMPROVED ELECTRIC METER "
My Invention relates to apparatus for measuring and indicating electrical
currents in a circuit. Hitherto instruments for this purpose have been more or less
dependent on the action of permanent inagnets or springs, and the indications given
by them are apt to be erroneous, on account of variations in the magnetic intensity
of such magnets, or the variation in the elasticity of the springs employed, due to
various causes.
To avoid these defects, I construct an Electric Meter in the following manner.
On a horizontal axis, I fix near one end, an index or pointer of light material,
and also on the axis parallel with the pointer, I fix a needle of soft iron, the pointer
and needle being normally maintained in a vertical attitude by means of a counter-
weight suspended from the axis. Immediately under the soft iron needle, is placed
a vertical electromagnet which magnetises the needle when a current is passed
through its coils. On each side of the soft iron needle is a helix of insulated wire,
so that, on the current being passed through these helices, the needle being
attracted by the one and repelled by the other is deflected, and the pointer indicates
the amount of deflection on a graduated scale.
When the instrument is intended to be used for measuring currents, the coil of
the electromagnet and the helices should be of thick wire having low resistance.
If the instrument is to be used as a power meter, the mechanical construction
remains the same, but the coil of the electromagnet, instead of being of low
resistance, is of fine wire, of high resistance, and instead of being along with the
Clemira All

page_text: .
helices in the main circuit, the electromagnet is in a by-pass circuit between the
points of the circuit in which the power is to be measured.
For use as a Volt-meter, the whole instrument is wound with fine wire to a high
resistance.
It is obvious that a solenoid may be used instead of the electromagnet.
As a change in the direction of the current flowing through the coils of the
instrument causes a reversal in the polarity of the induced needle, as well as a
reversal in the polarity of the needle coils, the deflection is independent of the
direction of current, and the instrument is applicable for indicating alternate, as
well as continuous currents.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said William McWhirter in the Patent Office on the 17th January
1884.
2
WILLIAM MCWHIRTER of 219/ Argyle Street Glasgow in the County of Lanark
North Britain "A NEW OR IMPROVED ELECTRIC METER
"
My invention relates to apparatus for measuring and indicating electrical
currents in a circuit. Hitherto instruments for this purpose have been more or less
dependent on the action of permanent magnets or springs, and the indications
given by them are apt to be erroneous, on account of variations in the magnetic
intensity of such magnets, or the variation in the elasticity of the springs employed,
due to various causes.
To avoid these defects, I construct an electric meter as shewn in the accom-
panying drawings, Fig. 1 is a front view, the dial being supposed to be removed to
shew the interior, Fig. 2 is a vertical section, and Fig. 3 is a plan. Fig. 4 is an
end view of the axis.
On a horizontal axis A 1 fix near one end, an index' or pointer C of light
material, and also on the axis parallel with the pointer C I fix a needle B of soft
iron, the pointer and needle being normally maintained in a vertical attitude by
means of an adjustable counterweight D suspended from the axis A. Immediately
under the soft iron needle B is placed a vertical electro-magnet M which magnetises
the needle by induction when a current is passed through its coils. On each side
of the soft iron needle B is a helix E of insulated wire, so that, on the current
being passed through these helices, the needle B is deflected, and the pointer C
indicates the amount of deflection on a graduated scale marked on a dial F.
When the instrument is intended to be used for measuring currents, the coil of
the electro-magnet M and the helices E should be of thick wire having low
resistance.
If the instrument is to be used as a power meter, the mechanical construction
remains the same, but the coil of the electro-magnet M, instead of being of low
resistance, is of fine wire, of high resistance, and instead of being, along with the
helices, in the main circuit as shewn, the electro-magnet M is in a by-pass circuit
between the points of the circuit in which the power is to be measured.
For use as a Volt-meter, the whole instrument is wound with fine wire to a high.
resistance.
It is obvious that a solenoid may be used instead of the electro-magnet M, the
iron core of the electro-magnet being dispensed with.
As a change in the direction of the current flowing through the coils of the
instrument causes a reversal in the polarity of the induced needle B as well as a
reversal in the polarity of the needle coils E, the deflection is independent of the
direction of current, and the instrument is applicable for indicating alternate,
as well as continuous currents. One of the coils E may be dispensed with, or the
two coils may be of different powers, the one or the other being brought into use
by a switch. The soft iron needle B may be made of various forms some of which
are shewn in Fig. 5. Also the working parts may be so arranged that the needle
hangs down from its axis, in which case the counterweight can be dispensed
with.
Having thus described the nature of my invention and in what manner the same
is to be performed, I claim :-
In combination with the deflecting coil of an electric meter, a soft iron needle

page_text: fixed on an index axis and magnetised by induction from a neighbouring electro-
magnet or solenoid excited by the current to be measured or part thereof,
substantially as and for the purposes herein set forth.
In witness whereof I the said William McWhirter have hereunto set my
hand and seal this Fifteenth day of January in the year of our Lord One thousand
eight hundred and eighty-four.
WILLIAM MOWHIRTER. (L.S.)