Improvements in Galvanometers.
Year: 1894

page_text: Date of Application, 9th July, 1894
Complete Specification Left, 29th Mar., 1895-Accepted, 4th May, 1895
PROVISIONAL SPECIFICATION.
Improvements in Galvanometers.
I, JOHN HOPKINSON, F.R.S., of Westminster Chambers, 5 Victoria Street,
London S.W., do hereby declare the object of this invention to be as follows :-
My invention has for its object to secure that galvanometers whether ampere-
meters or voltmeters shall not be affected by currents other than the currents to
be measured and shall not exhibit errors arising from the hysteresis of iron or
steel.
The reacting parts of my galvanometers consist of a conductor carrying the
current to be measured and of an electromagnet or electromagnets the one being
movable the other fixed. The electromagnet or electromagnets have a core of
small section and expanding pole pieces opposed to each other, and are excited by
a current supplied by a source of electricity the potential of which does not vary
greatly. They are highly saturated so that any small variation in the potential
of the supply causes no appreciable variation in the magnetism, nor does it
cause any material difference whether the magnetising current is increasing or
diminishing.
The conductor for an amperemeter has preferably the form of a fixed plate of
copper passing between the expanded and opposing poles of the electromagnet or
electromagnets. The electromagnets are carried so that they can move as
system about an axis passing perpendicularly near the middle of the plate.
a
The conductor of a voltmeter has the form of a coil of fine wire and is
preferably movable whilst the electromagnet is fixed, has its poles expanded and
opposed to each other, and the coil passes between the poles. But in this case the
coil may be fixed and the magnet movable almost as conveniently.
Either instrument can be arranged by suitable balance weights to measure
currents or potentials over any desired range and with any desired sensibility.
Dated this 9th day of July 1894.
JOHN HOPKINSON.
Improvements in Galvanometers.
I, JOHN HOPKINSON, F.R.S., of Westminster Chambers 5 Victoria Street
London, S.W., 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 :-
My invention has for its object to secure that galvanometers for measuring current
or amperemeters shall not be affected by currents other than the currents to
be measured, and shall not exhibit errors arising from the hysteresis of iron or
steel.
The reacting parts of my galvanometer, consist of a conductor carrying the
current to be measured and an electromagnet or electromagnets the one being
movable the other fixed. The electromagnet or electromagnets have a core or

page_text: cores of small section and expanding pole pieces opposed to each other and are
excited by a current supplied by a source of electricity the potential of which
does not vary greatly. They are highly saturated so that any small variation in
the potential of the supply causes no appreciable variation in the magnetism,
nor does it cause any material difference whether the magnetising current is
increasing or diminishing.
The conductor for the current to be measured has preferably the form of a fixed
plate of copper passing between the expanded and opposing poles of the electro-
magnet or electromagnets. The electromagnets are carried so that they can
move as a system about an axis passing perpendicularly near the middle of the
plate.
The amperemeter shown in the drawings consists of a fixed conductor A
carrying the current to be measured and two movable electro magnets B B¹
placed on either side of the conductor A. The magnets have cores C C¹ of small
section with expanded pole pieces D D¹ opposed to each other and in close
proximity to the conductor. The magnets are excited by a current of such
potential that their cores are highly saturated. The electromagnets are connected
together by bridge pieces E E and are suspended by wires or strips of thin flexible
metal F F which also serve to convey the current from the terminals G G¹ to
the electromagnets, the connection from magnet to magnet being conveniently
carried upon one of the bridge pieces E. An adjustable balance weight H
attached to the electromagnets serves to control the movements of the electro-
magnets and determine the range over which it is capable of working. Attached
to the electromagnet is a pointer J by which the deflection of the electromagnets
is read upon a dial K.
I do not limit myself to the precise construction shown in the drawings or to
the method described for carrying or suspending the electromagnet or electro-
magnets.
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 :-
A galvanometer consisting of a conductor carrying the current to be measured
and of an electromagnet or electromagnets movable in relation to the couductor,
the electromagnet or electromagnets having a core or cores of small section and
expanding pole pieces opposed to each other on opposite sides of the conductor
carrying the current to be measured and excited by a current supplied by a source
of electricity the potential of which does not vary greatly.
Dated this 29th day of March 1895.
JOHN HOPKINSON.