IMPROVEMENTS IN INSTRUMENTS FOR MEASURING ELECTRICITY
Year: 1885

page_text: I, LESLIE BRADLEY MILLER of 20 Bolan Street, Battersea, London Electrical
Engineer do hereby declare the nature of my invention for IMPROVEMENTS IN
INSTRUMENTS FOR MEASURING ELECTRICITY to be as follows:-
My invention relates to Instruments known as Ammeters and Volt-meters In
constructing one of my improved instruments I take a short length of thin soft
iron wire and attach to one end a pointer of aluminium or other metal. The iron
is pivotted in the middle and moves over a scale fixed on the surface of a vertical
piece of wood forming part of the framework of the instrument. Round the piece
of soft iron wire but not close to it I wind a coil of wire for conveying the current
to be measured. The plane of the convolutions of this wire forms an angle of
about 45° with the vertical needle but this angle can be varied by suitably
pivotting the metal reel on which the wire is wound.
When an electric current is passed round the coil the needlo takes up a position
due to its tendency to set parallel to the lines of force acting in opposition to
gravity.

page_text: Improvements in Instruments for Measuring Electricity.
I, LESLIE BRADLEY MILLER, of 20 Bolan Street, Battersea, London Electrical
Engineer do hereby declare the nature of my invention for MEASURING ELECTRICITY
and in what manner the same is to be performed, to be particularly described
and ascertained in and by the following statement:—
My invention relates to the Instruments known as ammeters and voltmeters.
My improvements have resulted in an instrument in which the errors due to the
use of permanent magnets, springs, or considerable masses of iron in the needle or
controlling magnets have been avoided. The instruments invented by me are
wholly electro magnetic in their action and controlled by gravity. They therefore
never require to be recalibrated. The iron needle is extremely small and moves in
a strong magnetic field and for this reason it is dead beat in its indications and
very little affected by its proximity to powerful magnets. The error (if any) due
to this last cause can be seen at once by reversing the commutator and taking the
mean reading.
;
In constructing one of my improved Ammeters or Voltmeters I wind a coil of
insulated wire, for conveying the current to be measured, on to a brass reel with a
hollow core.
This reel is fixed to a vertical surface screwed to a base provided
with levelling screws. The reel or bobbin can be turned on a centre through a
small angle and fixed at the desired position by means of a set screw.
The plane
of the convolutions of this coil, when no current is passing, form an angle of
about 45° with a soft iron needle that hangs vertically down inside the coil. This
needlo turns on a pivot placed just below and at one side of the coil and has u
downward continuation of aluminium or other metal that serves both as a pointer
to a scale of amperes or volts and also as a weight tending to bring the needle to
the zero or vertical position. The needle may either be made wholly of iron or,
preferably, only that part of it that is above the pivot and inside the coil, of this
metal, and the remainder of some non magnetic material. The weight of the
needle can usually be varied within the small limits required for calibration by
making the pointer too long at first and then clipping off the end, but a small
screw thread may be cut on the needle and the position of a nut working on it
altered as required.
Referring to the drawings Fig. 1 is a front elevation and Fig. 2 a sectional eleva-
tion of the instrument. In Fig. 2a is a soft iron needle turning on the pivot a¹, b is
the aluminium pointer and weight, c the scale divided into spaces corresponding to
equal increments of current, & the framework, e the solenoid, fa set screw for
fixing the coil at the same angle as that of the standard instrument from which
the scale plate is engraved.
When an electric current is passed round the coil the needle is magnetised and
tends to put itself parallel with the lines of force proceeding from the coil. This
action is opposed by the acting weight of the needle and pointer which increases as
they are pulled from the vertical line. The scale shown in the drawing is that
due to an iron needle extending both above and below the pivot but when the
under part is non magnetic the scale is more evenly divided. With the ammeters

page_text: I prefer to make use of a commutator that will reverse the current through the
instrument without breaking the circuit but with volt meters a commutator that
will also serve as a contact breaker.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is
1. In an electric meter wherein a soft iron needle controlled by gravity is used
in connection with a solenoid through which the electric current to be measured
passes and magnetises the needle the method of arranging the axis of the said
solenoid at an angle to that of the needle when in its zero position substantially as
described.
4
2. The electric meter constructed arranged and operating substantially as
described and shown in the drawings annexed.
.