Improvements in Electrical Measuring Instruments.
Year: 1897

page_text: Date of Application, 12th Nov., 1897
PROVISIONAL SPECIFICATION.
Improvements in Electrical Measuring Instruments.
We, GEORGE KEITH BULLER ELPHINSTONE, of 101, St. Martin's Lane, in the
County of London, Electrical Engineer, and ARTHUR CECIL HEAP, of The Firs,
Tyler's Green, Penn, in the County of Buckinghamshire, Electrical Engineer,
do hereby declare the nature of this invention to be as follows:-
:-
This invention has for its object the making of an instrument for use on
alternating current circuits for 'measurements of current strengths which shall
be practically independent of periodicity at which the current is supplied, and
variations of the shape of the curve of such currents.
An electro-magnet is used, the iron core being constructed of laminated plates,
and the poles are so shaped as to allow of the pivotted or suspended coil moving
in the annular, space between these poles. A fixed soft iron core piece may be
placed centrally with the moving coil. The amount of rotation er movement
of this coil can be controlled by gravity or springs, and it may carry an index
pointer or like. attachment serving to indicate or record the rotation
of the coil. By regulating the windings of the electro-magnet, which wind-
ings are preferably made up in sections, the magnetic flux in the iron may be
controlled. The windings of wire upon this electro-magnet are arranged in two
or more distinct sections according to the object for which the instrument is
intended.
When the instrument is intended for use as a voltmeter then we wind two
complete windings upon the electro-magnet core, one of which is connected to
the source of alternating current to be measured; a suitable non-inductive resis-
tance being connected in series with these coils according to the range or value
of the electromotive force to be dealt with.
Another distinct winding is provided on the cores of the electromagnet, the
extremities of which are directly connected to the moving coil which carries
the pointer, which coil is free to turn against the action of a spring or gravity
in the field of the electromagnet. The coil on the electromagnet, and the moving
coil between the poles forming, in fact, a secondary circuit, the currents flowing
in which are induced by the change of the magnetism produced in the electro-
magnet by the first mentioned windings.
We
We may arrange that the number of turns of wire on the two sections on the
electromagnet may be equal so as to produce the same electromotive force across
the extremities of the secondary windings on the electromagnet, as exists between
the extremities of the primary; or we may make the secondary windings on the
electromagnet of a larger number of turns, so that the electromotive force induced
in the secondary coil on the electromagnet may be considerably higher than the
electromotive force applied to the primary.
We can interpose a resistance in the connection between the secondary circuit
on the electromagnet and the coil which is free to move in the field.
Natambor 10th 1907

page_text: Improvements in Electrical Measuring Instruments.
We, GEORGE KEITH BULLER ELPHINSTONE, 101, St. Martin's Lane, in the
County of London, Electrical Engineer, and ARTHUR CECIL HEAP, The Firs,
Tyler's Green, Penn, Buckinghamshire, 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 has for its object the making of an instrument for use on
alternating current circuits for measurements of current strengths which shall
be practically independent of periodicity at which the current is supplied, and
of variations of the shape of the curve of such currents.
An electro-magnet is used, the iron core being constructed of laminated plates,
and the poles are so shaped as to allow of a pivoted or suspended coil moving
in the annular space between these poles. A fixed soft iron core piece may be
placed centrally with the moving coil. The amount of rotation or movement
of the coil can be controlled by gravity or springs, and it may carry an index
pointer or like attachment serving to indicate or record the angular displace-
ment of the coil.
By regulating the windings of the electro-magnet, which windings are prefer-
ably made up in sections, the magnetic flux in the iron may be controlled.
The windings of wire upon this electro-magnet are arranged in two or more
distinct sections according to the object for which the instrument is intended.
When the instrument is intended for use as a voltmeter, then we wind two
complete windings upon the electro-magnet core, one of which is connected to
the source of alternating current to be measured; a suitable resistance being
connected in series with these coils according to the range or value of the
electro-motive force to be dealt with.
The other winding has its extremities connected to the moving coil which
carries the pointer, which coil is free to turn against the action of a spring or
gravity in the field of the electro-magnet. Such secondary winding on the
electro-magnet and the moving coil between the poles forming a secondary
circuit, the currents flowing in which are induced by the change of the magnetism
produced in the electro-magnet by the first mentioned windings.
We may arrange that the number of turns of wire in the two sections on the
electro-magnet may be equal so as to produce the same E.M.F. across the ex-
tremities of the secondary winding as exists between the extremities of the
primary winding; or we may make the secondary winding on the electro-magnet
of a smaller number of turns, or, when required, of a much higher number of
tums, so that the E.M.F. induced in the secondary coil on the electro-magnet
may be considerably higher than the E.M.F. applied to the primary.
We can interpose a resistance in the connection between the secondary circuit
on the electro-magnet and the coil which is free to move in the field.
The accompanying drawing shows diagrammatically so much of an instrument
as is required to illustrate our invention.
The laminated core of the electro-magnet is shown at C. Upon this are
mounted eight coils A A which are all connected up in series, and the extremities
of the outside coils are carried to the binding post T T. These coils are dis-
tributed upon the core in pairs at four equi-distant points and a resistance A¹
may be connected into their circuit which may be either non-inductive or
partly non-inductive and partly wound as an impedance coil, or may be entirely

page_text: Uni-
wound as an impedance coil according to the requirements of special cases.
formly distributed between these coils are three coils B B B which are connected
up together. The wire from one end of the coils B is carried to the resis-
tance R, and the other end is joined to the moving coil E pivotally mounted
to turn in the gap between the poles of the core C. The other terminal of the
moving coil is joined to the resistance R. The coils B B B therefore, with the
resistance R, (which may be either entirely non-inductive or partly non-inductive
and partly wound as an impedance coil or may be entirely wound as an im-
pedance coil according to the requirements of special cases) and the moving
coil E form a complete circuit which is entirely distinct from any of the other
windings in the instrument. Other methods may be adopted for distributing
the windings on the core C. The object to be kept in view is that the two sets
of windings shall be as uniformly distributed as possible to avoid magnetic
leakage. The moving coil E is carried upon two pivots F and a pointer P is
connected to the moving coil so that its movements can be observed upon the
scale S. The turning action of the current through the coil E is opposed by
means of a weight W or any other suitable arrangement may be adopted for
this purpose.
Mounted centrally within the coil E, but entirely free from it
and supported from the frame of the instrument J, is a core H which may be
laminated, and the object of which is to keep the magnetic circuit of as low
resistance as possible.
In an organization of this kind magnetic leakage is substantially eliminated,
the energy of movement of the pivoted coil is considerable and angular move-
ment thereof indicates the current strength irrespective of its periodicity.
Obviously the instrument may be wound to act either as a volt-meter or am-
meter, and as an indicating or recording instrument or both.
The value of the resistance R may be adjusted to adapt the instrument to any
value of current strength; while the resistance A₁ may be used when it is not
desirable that the primary windings should have the full fall of potential across
them of the circuit in which they are connected.
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed, we declare that
what we claim is:-
1. The combination of the electro-magnet core, the primary windings disposed
thereon, the secondary winding, a pivoted or swinging coil mounted between
the poles of the core and included in closed circuit with said secondary winding,
and an indicating or recording device operated by the swinging coil.
2. The combination of the electro-magnet core, a series of connected windings
disposed at substantially equal intervals thereon, a secondary series of wind-
ings disposed upon the core between the windings of the first series, a pivoted or
swinging coil mounted between the poles of the magnet and included in closed
circuit with said secondary windings, and an indicating or recording device
operated by the swinging coil.