Improvements in Electrical Measuring Instruments.
Year: 1891

page_text: Date of Application, 19th Sept., 1891-Accepted, 24th Dec., 1891
COMPLETE SPECIFICATION.
Improvements in Electrical Measuring Instruments.
A communication from abroad by EDWARD WESTON, of Newark, in the County
of Essex and State of New Jersey, United States of America, Gentleman.
I, JOHN CORRY FELL of the firm of Fell & Wilding, of 1 Queen Victoria
Street in the City of London, Patent Agents, 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 is designed for the measurement of the force of strong electrical
currents of thousands of amperes, while it is constructed so that it may be used
with great advantage for the purposes of house telegraphy.
The instrument is arranged as follows:-
In the annular space between the poles of a permanent magnet is arranged a
movable bobbin. As this annular space contains a magnetic field, which is constant
and not influenced by the change of current, the movement of the bobbin is subject
only to the resistance of the circuit and the electro motive force respectively.
In consequence, however great the normal resistance of the circuit may be, it
cannot influence the action of the apparatus, and in the same degree very small
changes of resistance will influence the movements of the bobbin.
The construction of the magnet is such that the space in which the bobbin
works, with given magnetism, is magnetic to a high degree, so that the slightest
change within such space effected by a current passing through the bobbin effects
a change of position in the latter, or in other words the bobbin or coil will move
into a new position dependent on the strength of the current, in which it will remain,
until the strength of current or the resistance is changed. The transmission of the
movement of the coil or bobbin to the pointer is arranged so that a small move-
ment of the coil effects a very large movement of the pointer which is obtained by
the pitch of the thread on the pointer spindle.
In consequence this apparatus may be used for indicating the strength of the
current on a suitable scale, while it may also be used for any telegraphic purposes.
because the pointer occupies a certain position when the circuit is closed. When
used for telegraphic purposes the scale is marked in the usual manner; the apparatus
being particularly suitable for house telegraphy.
The normal resistance is practically without effect on this apparatus, two or more
of these instruments indicating exactly alike, whatever may be the length of the
circuit within practicable limits.
In order that my invention may be the better understood, I now proceed to
describe the same, reference being had to the accompanying drawings and to
the letters and figures marked thereon. Like letters refer to like parts throughout
the figures.
Figure 1 is a front view of the instrument, with part of the face or scale removed
to show the interior parts, and
Figure 2 is a sectional view on the line X X of Figure 1.
A is the base of the instrument, B is the casing, the front of which is closed by
the glass plate C through which the scale D can be observed. E is a tubular
pole piece, of iron or other magnetic material, having a flange F by means of which
it is attached to one set of poles of the magnets or to the base plate. G is
another tubular pole piece of iron or other magnetic material having a flange H
and is attached to the flange F of the pole piece by means of a brass ring 1, and
to the other poles of the magnets. The diameter of the pole piece E is smaller
than that of the pole piece G. I to I are permanent magnets, arranged radially
and connected to the flange H of the pole piece G and flange F of the pole piece E.

page_text: The pole pieces E and G therefore form part of the compound permanent magnet,
consisting of the six magnets I' to I. K is a cylinder of aluminium or other light
metal, closed at one end by means of the disc L and carrying a coil or bobbin M of
fine insulated wire. The cylinder K rests on a tube N extending through the pole
piece E and carried by two springs O and P attached to the brass ring I but
insulated from the latter by the transverse piece Q.
In the tube N moves a two threaded spindle R carried on the two pins S and U;
connected by the bent piece T carried by the bracket W which is attached to the
bracket a.
The pin U carries the pointer V. The bracket a is attached to the
pole piece.
The action of the instrument is as follows.
'
The current entering at the binding screw 1 passes through the wire c, spring O,
coil M, cylinder K, tube N, spring P, wire il, and leaves through the binding
screw 2.
In consequence the bobbin or coil M is drawn into the space between the pole
pieces, the degree of attraction being indirectly proportional to the resistance.
The movement of the coil M is transmitted to the pointer by means of two
pins e opposite each other and the two threaded spindle R into the thread of
which the pins enter.
The rotation of the spindle affects the bent piece T, whereby the movement is
transmitted to the pointer V and the latter is thus deviated.
Having now particularly described the nature of my invention and in what
manner the same is to be performed, I declare that what I claim is :-
In electrical measuring instruments an arrangement, characterised by a
permanent magnet, and consisting of six or other number of horse shoe magnets I¹
to I arranged concentrically to one another, the tubular pole pieces E and G
with flanges F and H connected to the pole ends of the magnets 1 to 1°, the
cylinder K with the coil or bobbin M in the annular field between the before
mentioned pole pieces, the springs O P carrying the before mentioned cylinder,
the scale D, the pointer V and the mechanism serving to transmit the rectilinear
motion of the coil M to the pointer V.
Dated thin 10th J
1001
FELL & WILDING,
1, Queen Victoria Street, London, E.C., Agents for the Applicant.