AN IMPROVED ELECTRO- METER
Year: 1884

page_text: ARTHUR WRIGHT (Electrical Engineer) Regent Foundry North Road Brighton
Sussex do hereby declare the nature of my invention for AN IMPROVED ELECTRO-
METER to be as follows:-
An electrometer consisting of a moveable pear shaped plate (herein after called
the armature) capable of rotating in a plane slightly inclined to that of a fixed
plate placed very close to it.
The two points, between which it is desired to measure the difference of
potential, are connected to the armature and fixed plate respectively, and the
attraction between these plates, consequent on their difference of potential, causes
the armature, in its endeavour to get nearer the fixed plate, to move through
a certain angle from its zero position until an opposing force, such as gravity or
that of springs, which tends to keep it at its zero position, balances this attraction.
The amount of rotation forming a definite measure of the difference of potential
required.
The armature is so adjusted that when at its zero position, the distance between
it and the fixed plate is greater than when it is at any other point of its path.
Instead of one fixed plate two may be used one on each side of the armaturé
which may extend on both sides of its axis and be of a dumb bell shape.
}
The fixed plate or plates instead of being perfectly flat may be slightly curved or
be part of a screw surface in order to obtain increased sensitiveness or increased
range of deflection.
By applying an exceedingly delicate form of automatic commutator to the instru-
ment and a rotation counter to its axis, it may be made to continually rotate for
as long as the difference of potential is maintained and so integrate the values
during a certain time.

page_text: I, ARTHUR WRIGHT Electrical Engineer Regent Foundry North Road Brighton
Sussex do hereby declare the nature of my invention for AN IMPROVED ELECTRO-
METER 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 my invention is to obtain an electrometer with a large angular
range, but in which the attracting plates or surfaces are always close to one
another.
This I accomplish by making the moveable plate, hereinafter called the armature,
rotate in a path, either very slightly inclined to the fixed surfaces or slightly
excentric to them.
The following are some of the practical forms of my invention.
One consists of a nearly counterbalanced moveable pear shaped plate armature
capable of rotating in a plane slightly, inclined to that of a fixed plate placed very
close to it and concentric with its axis: The two points between which it is
desired to measure the difference of potential are connected to the armature and
fixed plates respectively, and the attraction between these two, consequent on their
difference of potential causes the armature, in its endeavour to approach the fixed
plate, to move. through a certain angle from its zero position until an opposing
force such as gravity or springs balances this tendency to rotate, caused indirectly
by the mutual attraction of the armature & fixed plate.
The amount of rotation thus forming a definite measure of the difference of
potential required.
The armature is adjusted so that the average distance between it and the fixed
plate at its zero position; is greater than when it is at any other point of its path.
Instead of one fixed plate two may be used, one on each side of the armature,
each slightly inclining towards the armature's path, the armature may also extend
on both sides of the axis and be dumbell in shape, with another pair of fixed plates
acting on it.
The fixed plate or plates instead of being perfectly flat may be slightly curved or
be part of a screw surface, the object being to obtain increased sensitiveness or
range of deflection.
The armature in the forms described above may move in a vertical path or one
very nearly horizontal, according as the instrument is intended for the measure-
ment of high or comparitively low potentials the opposing force being in these
cases gravity, or similar forces Or it may move in a horizontal path with a hair
spring of a watch to bring it back to zero. The charge of electricity can be com-
municated to the armature through its axis.
Instead of the armature being a flat surface and in a plane at right angles to its
axis it may be made in the form of part of a cylindrical surface, capable of rotating
on its axis close to one or more cylindrical surfaces, slightly excentrically placed to
the armature's path, but extending round a considerable angle, these are so placed
that the average distance between the armature's surface and the fixed ones gets
gradually less as the armature moves from its zero position, but the two approach

page_text: one another so slowly that the armature may have to rotate through an angle
of 90° or 180° for the distance to diminish a small fraction of an inch.
Another form consists of a circular or partially so, armature moving between
two similar circular plates, placed very close & parallel to it the armature's axis
does not however pass through its geometrical centre but is slightly excentric to it,
also to the centres of the fixed plates, in such a manner that when the armature
moves it gets more or less concentric with the fixed plates, the zero position being
that of maximum excentricity & the attraction between the oppositely charged
plates tends to make the armature rotate into a position of less excentricity, until
the opposing force balances the attraction.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is
The above methods or any combination or variety of them for making an
electrometer with a very large angular deflection range, but in which the distance
between the armature, or moveable plate, and the fixed ones varies very slightly.