Improvements in Galvanometers.
Year: 1890

page_text: Date of Application, 29th Mar., 1890
Complete Specification Left, 24th Dec., 1890-Accepted, 24th Jan., 1891
PROVISIONAL SPECIFICATION.
Improvements in Galvanometers.
I, JOHN PERRY, Professor of Engineering Fellow of the Royal Society, of the
Finsbury Technical College London E.C. do hereby declare the nature of this
invention to be as follows:-
The Ayrton & Perry solenoid form of galvanometer is well known. It is described
in the Patent Specification No. 2156 of 1883 page 8 line 22 to page 10 line 14. It
consists of a coil of wire through which the current passes which is to be measured
& into the hollow internal space in the coil a thin tube of iron or bundle of iron wires
is attracted, thus exerting an axial force on an Ayrton & Perry spring the amount of
which force is indicated by the rotation of a pointer; or in electro-dynamometers the
attracted object is a coil of wire in which current is flowing, the attractive or
repulsive force as before being measured by an Ayrton & Perry spring. The present
invention is an improvement on this old instrument, whose dial could only be hori-
zontal, to enable the dial to be vertical or to be in any other direction, so that the
instrument may be attached to a wall or a switch board. The attracting coil's axis
being nearly horizontal, the attracted object whether an iron core or another coil is
slung by fine wires or strips of material so that it may have a motion like that of the
bob of a pendulum or rather of a battering ram. I prefer to use two wires or strips
for each sling the two making an angle with one another in the form of the letter V ;
this gives lateral stability.
The attracting field of the coil is increased if strips of iron pass from near the
aperture at one end, outside the coil to near the aperture at the other end or if the
ends & curved surface of the coil are covered with sheet iron. Some error is always
introduced, however by using iron & 1 generally use one strip only on the lower side
so as to give greater stability to the attracted object by making the lower part of the
magnetic field in which it moves, the more intense part.
The attracted object does not rotate about its axis, it is the remote end of the spring
which rotates, being pivoted so that it may not move axially.
The pointer on the rotating end of the spring is carefully balanced.
COMPLETE SPECIFICATION.
Improvements in Galvanometers.
I, JOHN PERRY, Professor of Engineering Fellow of the Royal Society, of the
Finsbury Technical College London E.C. 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 Ayrton & Perry solenoid form of galvanometer is well known. It is described
in the Patent Specification No. 2156 of 1883 page 8 line 22 to page 10 line 14. It
consists of a coil of wire through which the current passes which is to be measured,
and into the hollow internal space in the coil a thin tube of iron or bundle of iron
wires is attracted, thus exerting an axial force on an Ayrton & Perry spring, the
amount of which force is indicated by the rotation of a pointer; or in electro
dynamometers the attracted object is a coil of wire in which current is flowing, the
attractive or repulsive force as before being measured by an Ayrton & Perry spring.
All such instruments I shall in future refer to under the name Ayrton & Perry
instruments." The attracted object whether an iron core or another coil I shall call
[Price 4d.]
"

page_text: the armature. The present invention is an improvement on the old forms of Ayrton
& Perry instruments to enable the dial to be vertical, or to be in any other direction,
so that the instrument may be attached to a wall or a switch board. When the axis
of the armature is nearly horizontal & the armature is therefore to have a nearly
horizontal motion, the armature is slung by fine wires or strips of material or in other
ways so that it may have a motion like the bob of a pendulum or rather of a battering
ram. I prefer to use two wires or strips for each sling, the two making an angle with
one another in the form of the letter V; this gives lateral stability. Sometimes the
suspending pieces are rigid and rigidly attached to the armature being pivoted in
such a way as to allow the armature to move nearly axially. The important thing is
that the armature should be suspended so as to have a motion like that of a battering
ram. Either of these kinds of suspension may be used even when the axis makes
almost any angle with the vertical. When wires & strips are used & the armature is
a coil the wires or strips may serve to convey currents to the armature. The attracting
field of the coil is increased if strips of iron pass from near the aperture at one end
outside the coil to near the aperture at the other end, or if the ends & curved surface
of the coil are covered with sheet iron. Some error is always introduced however by
using iron & I generally use one strip only on the lower side so as to give greater
stability to the attracted object by making the lower part of the magnetic field in
which it moves the more intense part. The attracted object does not rotate about its
axis; it is the remote end of the spring which rotates being pivoted so that it may
not move axially.
This method of using the Ayrton & Perry spring is now well known & is described
& figured in Patent Specification No. 7802 of 1887. The pointer on the rotating end
of the spring is carefully balanced.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, 1 declare that what I
claim is :
I. The modification of the Ayrton & Perry instruments by which the armature is
so suspended as to have a nearly axial motion, whether the axis is horizontal or in
any other position, substantially as described.
II. In modified Ayrton & Perry instruments, the armature being suspended so as
to have a nearly axial motion, the use of the Ayrton & Perry spring one end being
fastened to the armature, the other end which is pivoted & not allowed to move
axially, being the rotating end.
Dated this 22nd day of December 1890.
JOHN PERRY.