Improvements in Electrical Measuring Instruments.
Year: 1894

page_text: Date of Application, 15th Jan., 1894
Complete Specification Left, 12th Oct., 1894-Accepted, 17th Nov., 1894
PROVISIONAL SPECIFICATION.
Improvements in Electrical Measuring Instruments.
I, HAYDN THIES HARRISON, of Trafalgar House, Great Newport Street, in
the County of London, Electrical Engineer, do hereby declare the nature of this
invention to be as follows:-
This invention of improvements in electrical measuring instruments has reference
to an improved electro-magnetic movement to be used in ammeters and voltmeters
to measure direct or alternating currents, and in which I take advantage of two
forces, namely, the repulsive force between two similarly magnetized pieces of soft
iron, and the attractive force exerted in a magnetic field on a movable piece of iron
by two pieces of soft iron fixed at either end of it but not in the same straight line
as it. By this combination I am able to produce an instrument containing less
iron than such as are now in general use, and one which has less error due to
hysteresis in the iron, because in an instrument according to my invention the
tendency of the iron exerting the repelling force is to demagnetize the movable
iron, whereas the other two fixed pieces of iron tend to magnetize the movable
iron. Such an instrument can be conveniently constructed as follows:-Within
a bobbin on which the wire is wound is placed a plug comprising two brass ends
fixed rigidly together by two pieces of brass strip fastened on either side of the
end pieces the whole being constructed so that it can be pushed into the centre of
the said bobbin.
A spindle of brass or other non-magnetic material is pivoted in two jewelled
Ecrews fixed into the end pieces, the one end piece is allowed to project a sufficient
distance in front of the coil to allow a pointer, fixed on the spindle between it and
the coil, to swing freely over an arc of 130 degrees.
On the spindle, the movable iron, consisting of a piece of soft iron wire or strip
about half the length of the coil, is fixed, by means of a metallic support which
holds it a short distance (say about inch) from the spindle and in such a way
that when the pointer moves to 130 degrees the iron will pass from being in close
proximity to the top of one of the brass supporting strips to the other brass
supporting strip; on the top of the first above mentioned brass strips is fixed a
piece of thin soft iron wire or strip, parallel to the centre of the coil, the same
length as the movable iron; thus when the pointer stands at zero the movable iron
lies parallel to the piece of fixed iron in close proximity to it. On top of the
other brass strip are fixed two pieces of iron, slightly less than one quarter of the
length of the coil, and over half a length of the coil apart from each other. These
two pieces of iron are also fixed parallel to the centre of the coil, and in such a
way that when the pointer is deflected to its maximum deflection, the movable iron
will be very nearly in the same straight line with them. The controlling force
used to act against the magnetic force is either gravity or a spring as may be
found most convenient. The action of the instrument so constructed is as follows:-
When there is no current passing through the coil the pointer is held at zero by
means of the controlling force, the movable iron being in close proximity to the
similar length of fixed iron; directly the current passes through the coil, the
movable iron and the fixed piece of iron, being similarly magnetized, repel each
other and as the current is increased the movable iron is repelled further, and
enters into the field of the two pieces of fixed iron, and is attracted towards them
(as it tends to lower the magnetic resistance of the air gap between them). The
attraction increases as the magnetization of the iron induced by the coil increases.

page_text: The reverse action takes place when the current diminishes. Thus the deflection
of the iron which is proportionate to the current is shown by the pointer.
When the instrument is required to measure current, a small number of turns
of thick wire are wound on the bobbin; when required as a voltmeter, a fine wire
winding of high resistance is used.
Dated this 15th down of Tenua 1204
COMPLETE SPECIFICATION.
Improvements in Electrical Measuring Instruments.
I, HAYDN THIES HARRISON, of Trafalgar House, Great Newport Street, in
the County of London, 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 of improvements in electrical measuring instruments has reference
to an improved electro-magnetic movement to be used in animeters and voltmeters
to measure direct or alternating currents, and in which I take advantage of two
forces, namely, the repulsive force between two similarly magnetized pieces of soft
iron, and the attractive force exerted in a magnetic field on a movable piece of
iron by two pieces of soft iron fixed at either end of it but not in the same straight
line as it. By this combination I am able to produce an instrument containing
less iron than such as are now in general use, and one which has less error due to
hysteresis in the iron, because in an instrument according to my invention the
tendency of the iron exerting the repelling force is to demagnetize the movable
iron, whereas the other two fixed pieces of iron tend to magnetize the movable
iron.
Such an instrument can be conveniently constructed as I will now proceed to
explain by the aid of the accompanying drawings in which,
Fig. 1 shows partly in vertical section and partly in elevation a volt meter
constructed according to this invention.
Fig. 2 is an underside view of the indicating portion or electro-magnetic movement
of the meter; and
Fig. 3 is a cross section thereof on the line of Figs. 1 and 2.
Within a bobbin 1 on which is wound the wire coil 2 the current passing through
which is to be measured, is placed a plug of non-magnetic material comprising two
brass ends 3, 3" connected rigidly together by two brass side strips 3b, 3º, the whole
being constructed so that it can be pushed into the hollow centre of the said
bobbin. In the example shown, the parts 3 3ª 3° 3° are cast in one piece of brass,
but they may obviously be in separate pieces suitably secured together, if desired.
4 is a spindle of brass or other non-magnetic material, pivoted in two jewelled
screws 5 fixed into the end pieces 3 3* the end piece 3 being allowed to project a
sufficient distance in front of the coil 2 to allow a pointer 6, fixed on the spindle
between it and the coil, as shown in Fig. 1, to swing freely over an arc of
130 degrees.
On the spindle the movable iron 7, consisting in the example shown of a narrow
thin strip of soft iron about half the length of the coil 2, is fixed by means of a
brass or other non-magnetic support 8 which holds it a short distance, say about
inch, from the spindle, and in such a way that when the pointer moves through
130 degrees from its zero position, the iron will pass from being in close proximity
to the bottom of the brass supporting strip 3" to the other brass supporting strip 3.
On the bottom of the first mentioned brass strip, viz. 3, is fixed a piece 9 of thin

page_text: soft iron strip arranged parallel to the axis of the coil 2 and of about the same
length as the movable iron 7; thus when the pointer stands at zero, the position
shown in Fig. 3, the movable iron 7 lies parallel to the piece 9 of fixed iron in close
proximity to it. On the bottom of the other brass strip, riz. 3°, are fixed two
pieces 10, 10% of thin strip iron, slightly less than one quarter of the length of
the coil, and over half a length of the coil apart from each other. These two
pieces 10, 10% of iron are also fixed parallel to the axis of the coil, and in such a
way that when the pointer is deflected to its maximum deflection as shown in
dotted lines in Fig. 3 the movable iron 7 will be very nearly in the same straight
line with them as shown in Fig. 2. The controlling force used to act against the
magnetic force, is either gravity, or a spring, as may be found most convenient.
In the example shown, it is a small weight 11 adjustably mounted on a pin 12
fixed to the spindle 4. 13 is part of a brass or other non-magnetic casing carried
by a base piece or support 14 and on the face of which is a suitable scale over
which the pointer 6 works.
The action of the instrument so constructed is as follows:-When there is no
current passing through the coil 2, the pointer 6 will be held at zero by means of
the controlling force, viz. the weight 11 in the example given, the movable iron 7
being in close proximity to the similar length of fixed iron 9. Directly a current
passes through the coil, the movable iron and the fixed piece of iron, being similarly
imagnetized, repel each other; and as the current increases, the movable iron will
be repelled further and will enter into the field of the two pieces 10, 10% of fixed
iron, and be attracted towards them, as it tends to lower the magnetic resistance
of the air gap between them. The attraction will increase as the magnetization
of the iron induced by the coil 2 increases. The reverse action will take place
when the current diminishes. Thus the deflection of the iron 7 which is
proportionate to the current, will be shown by the pointer 6 working over a suitable
scale.
When the instrument is required to measure current, a small number of turns
of thick wire are wound on the bobbin 1; when required as a voltmeter, a fine
wire winding 2 of high resistance is used, as in the example shown.
As will be obvious the spindle instead of actuating a pointer may actuate a
recording device.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. An electrical measuring instrument in which the strength of a current passing
through a coil is measured by means of the combined repulsive force set up
between two pieces of soft iron magnetized by the current and one of which is
movable and connected with a pointer or recording device, and the attractive force
exerted, in a magnetic field, on the said movable piece of iron by two pieces of
soft iron fixed at opposite ends of it but not in the same straight line as it,
substantially as herein described.
2. In an electrical measuring instrument, the combination with a coil through
which the current to be measured passes, of an electro-magnetic movement
constructed arranged and operating substantially as herein before described with
reference to the accompanying drawings for operating the indicating portion of the
instrument.
.
HAYDN THIES HARRISON.
W. Lloyd Wise,
46, Lincoln's Inn Fields, London, W.C., Applicant's Agent.