Improvements in Instruments for Measuring Electricity.
Year: 1891

page_text: Date of Application, 5th Mar., 1891
Complete Specification Left, 4th Dec., 1891-Accepted, 9th Jan., 1892
PROVISIONAL SPECIFICATION.
Improvements in Instruments for Measuring Electricity.
LESLIE BRADLEY MILLER & MAURICE WALTER WOODS both of 34 Gray's
Inn Road London Electrical Engineers do hereby declare the nature of this
invention to be as follows:-
Our invention relates to the electrical measuring instruments known as ammeters
and voltmeters. The construction of our improved instruments is as follows:-A
brass reel on which the insulated wire is wound has a hollow central tube which
contains an axis working on suitable pivots. The reel is fixed to a vertical support
forming the back of a circular case with its axis horizontal. The axis carries two
small brass arms holding short and light bundles of soft iron wire parallel with it
and in a line with one another. On the opposite side of the axis there is an
aluminium pointer that balances the iron and fixed to the axis is a small adjustable
weight for bringing the needle to zero. This arrangement combined with the
after mentioned disposal of the magnetic field results in the needle being nearly
dead beat in its movements. A piece of thin sheet iron wedge shaped as seen
from above is bent round inside the central tube and fixed in such a position that
the narrow end comes between the inner ends of the two bundles. As the needle
moves round the inner ends of the iron bundles approach the wide end of the fixed
part and by variation in the width of the narrow end of this fixed part the divisions
of the scale may be made of any desired size.
Dated this 5th day of March 1891.
LESLIE B. MILLER.
MAURICE W. WOODS.
COMPLETE SPECIFICATION.
Improvements in Instruments for Measuring Electricity.
We, LESLIE BRADLEY MILLER, & MAURICE WALTER WOODS both of
34 Grays Inn Road, London in the County of Middlesex Electrical Engineers do
hereby declare the nature of this invention and in what manner the same is to
be performed, to be particularly described and ascertained in and by the following
statement:
This invention relates to the instruments used for measuring electricity known
as ampere-meters and volt-meters.
The object we had in view was to make an improved instrument which should
have :-
(1.) A scale which should be either evenly divided or widen out towards the
end as might be desired. (2.) Little iron in its construction. (3.) Fairly dead
beat action.
The construction we have adopted to attain these ends will be seen from the
drawings annexed where
Fig. 1. is a front view on a reduced scale of the finished instrument (a volt
meter).
Fig. 2. is a plan of the core of the coil on which the wire is wound, the bobbin
being shown in section. The small iron bundles A, A, seen through square holes
in the brass core piece, are attached by small arms to a central axis turning in
jewels and carrying at one end a small adjustable weight B which brings the
aluminium needle C to the zero point of the scale, the iron and the aluminium
needle being balanced against one another. D. is a wedge shaped piece of thin

page_text: sheet iron bent into a circular shape round the outside of the core on a diameter
slightly larger than that of the circle described by the iron bundles A. A. so that
part of the weight may be taken off the pivots.
Fig. 3. is a side view of the iron bundles A. A., of the controlling weight B, of
the needle or pointer C, and of the fixed iron D.
Fig. 4. shows the iron bundles and the wedge piece D shaped in such a form as
to obtain an evenly divided scale.
Fig. 5. shows the shape of the iron D when a scale is desired that opens out
similarly to that shown in Fig. 1.
The action of the instrument is as follows:-When a current is sent round the
coil the iron pieces A. A. and the fixed piece D all become magnetised. It is the
property of a magnetic circuit that it has a tendency to shorten itself and there-
fore the iron bundles A. A. have a tendency to move towards the broader part of D
where the air gaps in the magnetic circuit are not so wide. This tendency is
opposed by the adjustable weight B.
It will readily be seen that the attraction between the pieces A. A. and D can
be varied by altering the shape of D and therefore the scale can be made to open
out or not as may be desired.
Instead of using two bundles of iron on the moving portion we may use only
one, and instead of one fixed piece of iron we may use two or more.
Having now particularly described and ascertained the nature of our said inven-
tion, and in what manner the same is to be performed, we declare that what we
claim is 11
1. In an electrical measuring instrument the combination of one or more small
bundles of iron moving round a centre, with one or more wedge shaped pieces of
iron fixed on or near the periphery of the same circle, and an adjustable
weight acting vertically; as described in this Specification and shown in the
drawings annexed.
2. The improved measuring instrument arranged and operating substantially as
herein described and shown, for the purpose set forth.
Dated this 3rd day of December 1891.
LESLIE BRADLEY MILLER.
MAURICE WALTER WOODS.