IMPROVE- MENTS IN INSTRUMENTS FOR MEASURING ELECTRICITY
Year: 1884

page_text: I, LESLIE BRADLEY MILLER, 20 Bolan Street, Bridge Road Battersea, S W.
Electrical Engineer do hereby declare the nature of my invention for IMPROVE-
MENTS IN INSTRUMENTS FOR MEASURING ELECTRICITY to be as follows:-
In the specification of my Patent No 1560/84 I have described an instrument
for measuring in practical units the strong currents and wide differences of poten-
tial employed in electric lighting. The invention I am now about to describe is for
measuring currents weaker than those which can be advantageously measured by
my earlier invention, such as those used in telegraphy and telephony and is more
especially suitable for making reliable tests of single galvanic cells.
In carrying out one form of my invention I take a very light strip of soft iron
(hereafter called the needle) and pass it through a hole bored in the centre of
another piece, of the same length, but considerably thicker, pivotting it so that it
can turn about its centre. I prefer to make a right angled bend in the middle of
the thick piece of iron, and fix it in a vertical position, so that the needle can hang
straight downward when the lower end is weighted by the addition of an aluminium
pointer which then points to the zero mark on a scale of degrees. Around the
centre of the two pieces of iron, for conveying the electric current, I wind insulated
wire the resistance and method of joining up of which varies in a manner well
understood according as it is desired to measure amperes, volts, or volt-amperes.
The bobbin on which this is wound is so shaped that while the wire is brought as near
the iron as possible it will not prevent the needle deflecting through an angle of,
say, 45°
When an electric current is passed through the coil the lower end both
of the soft iron needle and the thicker piece of iron become magnetised with, say,
N polarity and the upper ends of both with S polarity. The needle is therefore
repelled at both ends and turns round on its pivot away from the fixed piece
through an angle depending on the current passing thro' the coil, the proximity of
the deflected needle to the wire, the weight tending to bring the needle back to
zero &c. By making all the parts of dimensions I have found by experiment to be
correct, the angle of deflection may be made proportional to the tangent of tho
angle on a tangent galvanometer, i.e, to the current, and by adjustment of the
weight tending to bring the needle to the zero mark the deflection may be read off*
in any convenient units. I can however when necessary make use of an adjusting
piece of soft iron to make the deflection proportional.
I can vary the construction of the instrument as given above without departing
from the essential points of the invention which are the use of a single coil to cause
repulsion between the parts of a soft iron core, divided longitudinally, in such a
manner that the angle of deflection is a measure of the current strength.
Dated this 7th dow of Anril 100.1

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 and in what manner the samo is to
be performed, to be particularly described and ascertained in and by the following
statement
In the Specification of my patent No 1560, 1SS4 I have described an instrument
for measuring in practical units the strong currents and high electro motive forces
used in electric lighting. The invention I am now about to describe can be used
for the same purposes but is also suitable for measuring the weak currents to be
obtained from the ordinary galvanic cells used in telegraphy and for ringing
electric bells.
In carrying out one form of my invention I take a very light strip of soft iron.
(hereafter called the needle) and pass it through a hole bored in the centre of
another piece, of the same length but considerably thicker, pivotting it so that it
-can-turn-about-its-centre. I-prefer-to-make-a-bend-at-right angles in the middle.of
the thick piece and to fix it in a vertical position so that the needle will hang
straight downward when the lower end is weighted by the addition of an aluminium
pointer which then points to the zero mark on a scale of degrees. By making the
needle very light and thin it easily becomes saturated with magnetism and also
permits of the instrument being more dead beat in its action. Around the centre
of the two pieces of iron I wind insulated wire for conveying the electric current
to be measured. The resistance and method of joining up of this wire will vary
in a manner well understood according as it is desired to measure amperes, volts, or
volt-amperes. The bobbin on which this is wound is so shaped that while the wire
is brought as near the iron as possible it will not prevent the needle deflecting
through an angle of, say, 45°.
When an electric current is passed through the coil the lower end both of the
soft iron needle and the thicker piece of iron become magnetised with, say,
N polarity and the upper ends of both with S polarity The needle is therefore
repelled at both ends and turns round on its pivot away from the fixed piece
through an angle depending chiefly on the current passing through the coil and the
weight tending to bring the needle pointer to the zero mark. By making all the
parts of dimensions I have found by experiment to be correct and which may be
seen from the drawing, which is made to scale from one of the instruments con-
structed according to this invention the angle of deflection may be made proportional
to current strength, and by making the weight tending to bring the needle to zero
aljustable the deflection may be read off in any convenient units. I may however
make use of an adjusting piece of soft iron to make the deflection accurately pro-
portional to the current. This may consist of a small portion of iron held by a
brass cramp in any desired position, over the top or underneath the bottom of the
iron needle, in such a way that it tends to increase or lessen the deflection of the
needle in any part of the scale where such action is required; owing to the polarity
induced in it by the needle itself or by the needle and the fixed iron core. If the
instrument should be employed in a strong magnetic field a commutator which
reverses the direction of the current without breaking the circuit is useful as a
means of checking the readings and it may also be used to short circuit the coil.
In another form of the instrument I pivot the needle at one of the poles instead of
at the neutral line and I sometimes employ two needles, one on each face of a flat

page_text: soft iron core, so that when they are deflected the pointers attached to them move
away to the right and left of a cental zero line equal in length to the width of the
core between the needles.
Referring to the drawings, Fig 1 is a front elevation, Fig 2 a sectional elevation,
Fig 3 a plan. In Fig 2, A is the coil of wire for conveying the electric current to
be measured, B is the thick portion of the iron forming the core, C is the light soft
iron needle pivotted in the centre, D is a pointer formed of aluminium or other
me' al the weight of which tends to hold the needle C in a vertical position.
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
] claim is:
1. In an electric meter the use of a solenoid or coil provided with a soft iron
core formed in two or more parts so arranged with reference to each other and to
the said solenoid that when an electric current traverses the latter one or more
parts of the core is or are repelled by the other part or parts thereof with a force
that is a measure of the current strength, substantially as described.
2. The improved electric meter constructed arranged and operating substantially
as herein before described with reference to and shown in the drawings.
/1/0
LESLIE B. MILLER.