Improvements in Ammeters and Voltmeters..
Year: 1892

page_text: Date of Application, 19th May, 1892
Complete Specification Left, 16th Feb., 1893-Accepted, 22nd Apr., 1893
PROVISIONAL SPECIFICATION.
Improvements in Ammeters and Voltmeters..
We, JOHN PERRY of 31 Brunswick Square, London W.C., Fellow of the Royal
Society, and CHARLES EDWARD HOLLAND, Electrician, of 4 Redington Road,
Hampstead, London N.W. do hereby declare the nature of this invention to be as
follows:-
The object of our present invention is to so adapt the well known Ayrton & Perry
magnifying spring ammeters and voltmeters that they may have a vertical or other
dial so that they may be suitable for use fixed on a wall or switch board in any
position.
In the form of these instruments described in Patent Specification No. 2156 of
1883 there is a coil of wire wound on a vertical tube; a piece of soft iron is
attracted into this coil when a current flows through the wire, and the movement of
this iron is opposed by an Ayrton & Perry magnifying spring fixed to it at the
lower end.
The iron core rotates as it descends and the amount of this rotation is indicated
on a horizontal scale by a pointer attached to the upper end of the core.
In a more recent Patent Specification (J. Perry, No. 4921 of 1890) was described
a method of slinging the piece of soft iron by wires or flexible strips, one end of the
spring being fixed to the iron, the other end being pivoted & having a pointer
attached which rotated in a vertical plane.
The present invention is an improvement on these :—
We fix the piece of soft iron, or other armature, to a small lever, which is pivoted
in such a way that the armature may be attracted into a coil of wire when current
flows through the same, and we fix one end of the spring to the lever at some point.
If the instrument is to have a vertical scale this point is so arranged that it has
approximately a horizontal motion. The other end of the spring is pivoted and
has a pointer attached to it. The axis of the spring is horizontal, and consequently
the pointer moves in a vertical plane & the amount of its rotation may be observed
on a vertical scale, and this rotation indicates the current flowing through the coil.
The small lever may be of any shape & the axis of the coil in any direction; a
compact and convenient instrument is obtained by having the coil with its axis
horizontal, & a straight lever.
We also find it convenient to fix to some point of the lever a secondary spring the
tension in which may be adjusted by means of a screw or other appliance fixed to
the case of the instrument.
By means of this we are enabled to adjust the pointer accurately to zero without
disturbing the position of the instrument.
In order to increase the attraction of the core we sometimes surround the coil with
iron, with the exception of the central tube on which the coil is wound; sometimes
making the end cheeks of the coil of iron plates & placing an iron tube round the
outside of the coil.
Dated this 17th day of May 1892.

page_text: COMPLETE SPECIFICATION.
Improvements in Ammeters and Voltmeters.
We, JOHN PERRY of the City & Guilds Technical College, Leonard Street,
Finsbury, in the City of London, Professor, M.E., D.Sc., F.R.S., and CHARLES
EDWARD HOLLAND, of 4 Redington Road, Hampstead, London, Electrician, 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:-
The object of our present invention is to so adapt the well-known Ayrton and
Perry magnifying spring ammeters and voltmeters that they may have a vertical or
other dial so that they may be suitable for use fixed on a wall or switch board in
any position.
In the form of these instruments described in Patent Specification, No. 2156 of
1883 there is a coil of wire wound on a vertical tube; a piece of soft iron is
attracted into this coil when a current flows through the wire, and the movement of
this soft iron is opposed by an Ayrton & Perry magnifying spring fixed to it at the
lower end. The core rotates as it descends and the amount of this rotation is
indicated on a horizontal scale by a pointer attached to the upper end of
the core.
In the Specification of a more recent Patent (J. Perry, No. 4921 of 1890) was
described a method of slinging the piece of soft iron by wires or flexible strips, one
end of the spring being fixed to the iron, the other being pivotted and having a
. pointer attached which rotated in a vertical plane.
The present invention is an improvement on these. We fix the piece of soft iron
to one end of a small lever, which is pivotted in such a way that the iron may be
attracted into a coil of wire when current flows through the same, and we fix one
end of the spring to the lever at some point. If the instrument is to have a
vertical scale this point is so arranged that it has approximately a horizontal
motion; the other end of the spring is pivotted and has a pointer attached to it.
The axis of the spring is horizontal and consequently the pointer moves in a
vertical plane and the amount of its rotation may be observed on a vertical scale.
The small lever may be of any suitable shape and the axis of the coil in any
diréction; a compact and convenient instrument is obtained by having the coil with
its axis horizontal, and a straight lever. We also find it convenient to fix to some
point on the lever a secondary spring the tension in which can be adjusted by means
of a screw or other appliance fixed to the case of the instrument. By means of this
we are enabled to adjust the pointer accurately to zero without disturbing the
position of the instrument.
In order to increase the attraction of the core, we sometimes surround the coil
with iron, with the exception of the central tube on which the coil is wound; some-
times making the end cheeks of the coil of iron plates and placing an iron tube
round the outside of the coil.
Figure 1 of the accompanying drawings will serve to illustrate this invention and
is a section on the line 11 of Figure 2 through an instrument arranged within a
circular casing and having for convenience a circular face and glass with a scale
over which the index finger travels which is formed to the arc of a circle having the
pivot point of the index finger for its centre.
Figure 2 is a back view of the same instrument, like letters representing like
parts in both figures.
A is the coil, B the lever pivotted at B' and carrying the piece of soft iron C
which enters the central recess in the coil A, D is the "magnifying spring" secured
at D' to the lever B through which it passes the end of the spring being screw
threaded and carrying nuts D' by which the spring is secured in the lever; any
other suitable rigid connection may however be adopted. The lever B is cranked

page_text: at B and again at B' where it is connected with the spring E the other end of which
is connected to the arm F of a bell crank lever pivotted at F1 and having its other
arm F in contact with the regulating screw G which takes its bearing through the
wall of the metal or other case L. By this arrangement the index hand H can be
readily adjusted to zero by turning the screw G in so as to force the lever arm F'
inwards and so put slight tension upon the spring E, or withdrawing it so as
to allow the arm F' to move nearer to the case under the influence of the
spring E.
The operation of the magnifying spring D is the same as that described in the
above mentioned Specifications and need not be described here beyond the state-
ment that a very slight movement of the end D' in the direction of the axis of the
spring D by the lever B will cause the index finger H to travel over the whole of
its course across the face of the apparatus. This index finger is pivotted at H¹ to
the end of the magnifying spring D in such a manner that it partakes of the
circular movement imparted to this end of the spring (whose other end is not
allowed to turn in the lever B) by the tension placed upon it by the movement
of the lever B as will be well understood by reference to the Specification
No. 21563. I is the glass face and K is the scale over which the finger H
travels.
Having referred to the Specifications No. 215683 and No. 49210 it will be under-
stood that we do not seek to claim what is therein disclosed except in the special
combinations or arrangements herein set forth.
Having now particularly described and ascertained the nature of the said inveu-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
:-
1. In a measuring instrument such as described the combination with the
magnifying spring D of a lever such as B caused to oscillate by the attraction due
to the passage of an electrical current through a wire coil substantially as described
and illustrated in the accompanying drawings.
2. In a measuring instrument such as described the combination with the
magnifying spring D of a pivot lever such as B piece of soft iron C coil A. and
index finger H substantially as described and illustrated in the accompanying
drawings.
3. In a measuring instrument such as described the combination with the
magnifying spring D and lever such as B of a regulating or balancing spring such
as E substantially as described and illustrated in the accompanying drawings.
4. In a measuring instrument such as described the combination with the
magnifying spring D piece of soft iron C_coil A and index hand H of a lever such
as B B B spring E bell crank lever F F and regulating screw G the whole
substantially as and for the purpose described and illustrated in the accompanying
drawings.
5. The combination and arrangement of parts constituting the complete instru-
ment substantially as described and illustrated in the accompanying drawings.
Dated this 10th day of February 1893.
JOHN PERRY.
CHARLES EDWARD HOLLAND.
W. P. Thompson & Boult,
Agents for the Applicants.
JOHN PERRY.
CHARLES EDWARD HOLLAND.
W. P. Thompson & Boult,
Agents for the Applicants.