Improvements in Electrical Measuring Instruments.
Year: 1899

page_text: Date of Application, 13th Jan., 1899
Complete Specifination loft 12th And 4000
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Date of Application, 13th Jan., 1899
Complete Specification Loft, 13th Oct., 1900 Accepted, 18th Dec., 1800
Improvements in Electrical Measuring Instruments.
I, ARTHUR FREDERICK HARRIS, of Roslin, 57, Acre Lane, Brixton, London, S.W.,
Electrician do hereby declare the nature of this invention to be as follows:-
My invention relates to instruments consisting of a moving coil carrying a cur-
rent, and a permanent magnet, used either as ammeters for measuring current, or
as voltmeters for measuring potential differences.
The moving coil is of flat form being either circular rectangular or other con-
venient shape, and is of copper wire wound on a former of copper, aluminium
ivory or other suitable material.
This coil moves in a plane, instead of rotating about an axis as is usual with this
type of instrument and is attached to a spindle or arbor which is perpendicular
to the plane of the coil, by two arms, or in any other suitable mechanical manner;
The axis of rotation is without the coil and the arbor rotates in jewelled centres.
The coil moves in the gap of a permanent magnet, the poles of which may be
shaped in order to give pre-arranged results if found necessary.
The current is taken in and out of the coil by means of a metallic strip in the
form of a spiral, or by other suitable means. The controlling force may be either
spring or gravity control.
The movement of the coil may be observed by attaching a pointer to it, or in
any other suitable manner.
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Two coils may be used being connected either in "series or in parallel and the
two magnets arranged either astatically or otherwise.
Dated this 12th day of January 1899.
Improvements in Electrical Measuring Instruments.
I, ARTHUR FREDERICK HARRIS, of 57, Acre Lane, Brixton, S.W., in the County
of London, Electrical Engineer, 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 consists in the use of a thin flat coil moving in a plane at right
angles to its axis of pivotting or suspension, between the poles of a permanent or
electro magnet for the purpose of measuring currents of electricity; either used
SD 27

page_text: as a voltmeter or as an ammeter. In Figs. 1 & 2 an instrument for measuring
such currents is shown. Fig. 1 is a front elevation, Fig. 2 is a plan. M M are
two powerful permanent magnets having their pole faces P P P P in the same
plane, these faces may be flat as shown or shaped as found desirable, in the narrow
gap two coils C C move these coils are mounted on a pivotted staff a and are joined
up electrically in series or in parallel as occasion demands, so as to assist one
another the ends of the coils are brought on to two insulated washers W W to
which are attached two springs which form the controlling force of the instrument
& conduct the current to the two insulated wires TT which may form the terminals
of the instrument. To the top end of the staff or arbor a pointer is fixed by which
the motion of the coil may be observed this moves over a dial D as shown in Fig. 2
which dial may be graduated as required.
The coils C C are wound on formers of copper or aluminium or other suitable
material which serves the purpose of damping the oscilations, and may be circular,
rectangular or other convenient shape and are wound with copper wire of con-
venient diameter and then shellaced.
The arbor or staff carrying the coils is pivotted and moves between jewelled
screws J J which are carried by brass bridge pieces L L which also carry the
insulated pins to which the ends of the springs S S are fixed.
The magnets are supported on a brass base B by suitable clamps K K which also
support the dial, and the whole mounted in a case with a glass front in any manner
which may be found convenient. The shape of the coils, and the pole pieces are
governed by the style of scale required.
It has been found by experiment that a circular flat coil moving in a uniform
magnetic field as is approximately the case shown in the drawings, gives a scale
which is open in the middle & closes towards both ends, in other words the rate of
change of magnetic lines through the coil is not proportional to the angular
deflection.
If a very open scale is required the pole pieces may be made convex instead of
flat as shown, thus producing an intense and uneven magnetic field, the effect of
this is to open the scale greatly when the coil comes into the intensest region of
the lines of force.
Again by making the coil approximately retangular and the field uniform so
as to get the rate of increase in the number of lines cut by the coil proportional to
the angular deflection an even scale may be obtained.
Fig. 3 shows a plan of the coils with the top of the magnets removed in the
position they will take up at the end of a deflection.
Fig. shows section of the coils and the spirals of fine insulated wire joining
the ends of the coils to the insulated washers W W.
A single coil suitably balanced may of course be used if found convenient.
Having now particularly described the nature of my said invention and in what
manner the same is to be performed, I declare that what I claim is:-
I. The use of a thin flat coil moving in a plane perpendicular to its axis of
pivotting between the poles of a permanent or electro-magnet for voltmeters or
ammeters.
II. The variation of the shape of the coils or the shape of the pole-pieces of the
magnet to produce any desired scale.
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