Year: 1885

page_text: I, JOHN HUBERT DAVIES, of 73 Talgarth Road, in the County of Middlesex,
Electrical Engineer, do hereby declare the nature of this Invention to be as
follows:-
My Invention relates to instruments for measuring and controlling Electrical
Currents with great delicacy and accuracy, and by an appliance of great simplicity
and cheapness of construction.
My device consists essentially of two or more pieces of magnetic material freely
sliding or moving or revolving on a common support or axis, and which are so
placed, in magnetic fields or in parts of the same magnetic field, as to tend to move
the said support or axis in opposite directions of movement, but which do not
equally increase or decrease in their induced magnetism with an increase or
decease in the strength of the magnetic field acting upon them-By the respective
positions they are caused to occupy by the said variations in their induced
differential force, they indicate corresponding variations in the strength of the
magnetic field or fields, and consequently of the current or currents producing
them; and further at any chosen limits of such indications, my device may effect
electrical contacts, which may be utilised in a variety of known ways, to regulate
or control electrical currents.
To illustrate this action I will describe one convenient form of my device.
A coil of wire with,-say,-fifty turns-surrounds a very thin soft iron needle,
and another coil above with its axis parallel to the first and with, say, five turns
surrounds a much larger soft iron needle. The two needles are mounted on the
same axis but set at an angle to one another (conveniently rather less than 90°).
When a current is passed through the coils which are generally in series in one
circuit, each needle tends to place itself parallel to the axis of its coil and the two
needles thus exert an opposite or differential rotating effect upon the axis.
As the small needle is surrounded with a much larger number of convolutions
of the wire than the large needle, the deflecting force of the former with small
currents is greater than that of the latter; but when the current reaches a certain
value the small needle becomes magnetically saturated, and any further increase
in the strength of the current does not produce so large an increase of deflective

page_text: force on the small needle as it does on the larger which is of sufficient mass not to
be near magnetic saturation.
The axis and differential needles bearing a suitable pointer will thus take up
constant and definable angular positions relative to the coil or coils according to
the strength of the current traversing them, which may be indicated on a suitable
dial or scale, no division being marked on the dial until the current has become
strong enough to sufficiently saturate the smaller needle.
Instead of two coils of wire one only may be employed, the small needle being
placed inside the coil and the larger just outside the coil, the spindle to which the
needles are attached being in this case as in the last at right angles to the axis of
the coil.
Or the one coil may have the two needles inside it, the smaller one close to the
wire and the larger one in the axis or middle of the coil and therefore in a weaker
part of the magnetic field developed by the coil.
Or the magnetic field may be produced by an electro-magnet, the current passing
round which it may be desired to measure In this case the small needle would
be placed closer to the pole or poles of the magnet and consequently in a stronger
part of its field than the larger one.
Or, instead of obtaining an angular motion of the needles round a common axis,
a longitudinal sliding or suspended movement on a common support may be
produced by placing in a suitable position at one end of a solenoid or coil of wire
a large mass or rod preferably of iron and at the other end or inside the coil a
much smaller mass or rod the two being rigidly fixed together on a common
support, and suitably suspended, so as to be capable of a longitudinal motion in
the direction of the axis of the solenoid. The smaller mass of iron being placed
in a more intense part of the magnetic field than the larger, quickly becomes
magnetically saturated by the current in the solenoid. Although both the masses
of iron have an opposing tendency to enter the solenoid, the attraction exerted on
the larger mass increases more rapidly with increasing currents than that on the
smaller and so the system assumes constant and definable positions relatively to
the solenoid for various strengths of currents similarly to the case of the rotating
device.
In this form also two or more coils may be employed.
In all forms of my invention needles or masses of diverse magnetic materials,
such a nickel and iron, may be used so long as the rate of the increase or decrease
in their force produced by the variations in the strength of the magnetic field
or fields is diverse, either from the distinctive character of their material or the
difference in their mass.
When the current is alternating, it is desirable to make up the needles or masses
of thin plates or wires or in such forms as to facilitate rapid change of polarity.
The coils producing the magnetic field in my device may be of thick wire, and
the dial will then be graduated to show the value of the current in ampères; or
they may be of thin wire of high resistance to measure electromotive force, and
the dial will then be graduated in volts in a well known manner.
:
In this latter case the coils will become heated by long-continuance of the
current and their resistance will be thereby altered. To remedy this irregularity
I may introduce a compensating arrangement. To effect this the pointer of the
instrument is so arranged that it is capable of turning on the spindle or some
other portion of the moving parts, and motion is communicated from these parts
to it through a spiral or other suitably shaped thermostatic band constructed in
known manner of two or more strips of different metal, so as to move the pointer
on its spindle for variations of temperature in the coil A compensation by the
movement of the pointer or of the dial by the thermostatic band for changes of
temperature may thus be made, so as to counteract the errors of the indication of
the electro motive force affected by the change of temperature of the coil.
To increase the range of my instruments, I may make the relative positions of
the needles and the coil adjustable, so that, for instance, when the coils are noved

page_text: away from the needles to a certain point, the indications of the pointers have to
be multiplied by a known constant.
To control or regulate the current, I may attach to the moving parts of the
instrument a contact arm to work between two contact stops, so adjusted that
when a certain maximum or minimum limit of current passing through the coil or
coils has been reached, contact is made with one or other of these stops, whereby
a current is allowed to flow in properly arranged circuits to ring a bell or to
actuate any other apparatus to effect any required control or result.
To show the direction of the current when continuous, I may place a small
magnetised needle in a convenient part of the magnetic field produced by the
current, which needle shall be so marked or fitted as to indicate deflections to
either side and thus the direction of the current.
This magnetised needle is conveniently controlled and brought back to a middle
position by a light spring, so as to indicate either by a special indication or an
absence of any visible indication that no current is passing.
FELL & WILDING,
Agents for the Applicant..

page_text: COMPLETE SPECIFICATION.
Improvements in Instruments for Measuring and Controlling
Electrical Currents.
I, JOHN HUBERT DAVIES, of 73 Talgarth Road, in the County of Middlesex,
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 :—
My invention relates to instruments for measuring and controlling electrical
currents with great delicacy and accuracy, and by an appliance of great simplicity
and cheapness of construction.
My device consists essentially of two or more pieces of magnetic material or
their equivalents, freely sliding, moving, or turning on a common support or axis,
and which are so placed, in magnetic fields, or in parts of the same magnetic field,
as to tend to move the said support or axis in opposite directions of movement,
but which do not equally increase or decrease in their induced magnetism or their
magnetic force with an increase or decrease in the strength of the magnetic field
or fields acting upon them. By the respective positions they are caused to
occupy by the said variations in their differential force, they indicate corre-
sponding variations in the strength of the magnetic field or fields, and conse-
quently of the current or currents producing them; and further at any chosen
limits of such indications, my device may effect electrical contacts which may be
utilised in a variety of known ways, to regulate or control electrical currents.
To illustrate this action, will describe convenient forms of my device.
A coil of wire with, say fifty turns, surrounds a very thin soft iron needle, and
another coil above with its axis parallel to that of the first and with, say five
turns, surrounds a much larger soft iron needle. The two needles are mounted
on the same axis, but set at an angle to one another (conveniently rather less
than 90°). When a current is passed through the coils, which are generally in
series in one circuit; each needle tends to place itself parallel to the axis of its
coil, and the two needles thus exert an opposite or differential rotating effect upon
the axis. The small needle is surrounded with a much larger number of con-
volutions of the wire than the large needle, and the deflecting force of the former
with small currents is greater than that of the latter; but when the current
reaches a certain value, the small needle becomes magnetically saturated, and any
further increase in the strength of the current does not produce so large an
increase of deflective force on the small needle as it does on the larger, which is of
sufficient mass not to be near magnetic saturation. The axis and differential
needles bearing a suitable pointer, will thus take up definable angular positions
relatively to the coil or coils according to the strength of the current traversing
them, which may be indicated on a suitable dial or scale, no divisions being
generally marked on the dial until the current has become strong enough to
sufficiently saturate the smaller needle.

page_text: Instead of two coils of wire, one only may be employed, the small needle being
placed inside the coil, and the larger just outside the coil, the spindle to which the
needles are attached being in this case as in the last at right angles to the
magnetic axis of the coil,
Or, the one coil may have the two needles inside it, the smaller one close to
the wire and the larger one in the axis or middle of the coil, and therefore in a
weaker part of the magnetic field developed by the coil.
Or, the magnetic field may be produced by an electro magnet or electro magnets,
the current passing round which it may be desired to measure. In this case the
small needle would be placed closer to the pole or poles of the magnet and
consequently in a stronger part of its field than the larger one.
}
Or, instead of obtaining an angular motion of the needles round a common axis,"
a longitudinal sliding or suspended movement may be produced by placing in a
suitable position near or in one end of a solenoid or coil of wire a large mass or,
rod, preferably of iron, and at the other end, or inside the coil, a much smaller,
mass or rod, the two being rigidly fixed together on a common support, and
suitably suspended, so as to be capable of a longitudinal motion in the direction of
the axis of the solenoid. The smaller mass of iron more quickly becomes mag-
netically saturated by the current in the solenoid than the farger mass, and
although both the masses of iron have an opposing tendency to approach the
centre of the solenoid, the attraction exerted on the larger mass increases more
rapidly with increasing currents than that on the smaller, and so the system
assumes definable positions relatively to the solenoid for various strengths of
currents similarly to the case of the rotating device.
In this form also two or more coils may be employed.
In all forms of my invention needles or masses of divers magnetic materials
such as nickel and iron may be used so long as the rate of the increase or decrease
in their force produced by the variations in the strength of the magnetic field or
fields is diverse, either from the distinctive character of their material or the
difference in their mass; but I have hitherto found it advisable to use the
softest iron.
When the current to be measured is alternating, it is desirable to make up
the needles or masses of thin plates or wires or small pieces or in such forms as to
facilitate rapid change of polarity, and I sometimes find it an advantage to do this
for continuous currents.
In order that my invention may be the better understood, I now proceed to
describe the same in relation to the drawings hereunto annexed, reference being
had to the letters and figures marked thereon. Like letters refer to similar parts
throughout the drawings.
Figures 1 and 2 are a sectional elevation and plan of a completed instrument
carrying my invention into effect.
Figures 3 and 4 are an elevation and plan respectively of a modified form with
horse shoe electro magnet.
Figure 5 is a diagrammatic representation of the principle of my invention.
Figures 6 and 7 are an elevation and plan respectively of a further modified
form of my. device.
Figures 8 and 9 are an elevation and plan respectively of thermo regulator
applied to needle.
Figures 10 and 11 are an elevation and plan respectively of a further modified.
form of iny device.
Figure 12 is a diagrammatic elevation of a modification in which the coil is
substituted for one of the before described magnetisable needles.
Figure 13 is a diagrammatic representation of my device where a longitudinal or
sliding motion is employed.
Figure 5 represents diagrammatically the herein before first described form of
my invention. A is a coil surrounding the small needle D; B a coil surrounding
the larger needle C; P the pivot or axis to which the two needles are attached in

page_text: planes normal to that passing through the pivot, and at an angle with each other
of preferably nearly 90°. The coils A and B form parts of the same circuit, and
carry the current that it is desired to measure.
Figures 1 and 2 are respectively a section and a plan of the form in which only
one coil is used, and the large needle is placed outside this coil. A is the coil, shown
divided into two halves to allow room for the pivot; C the larger needle; D the
smaller needle inside the coil; E E¹ two brackets or plates having centres or jewel
holes in which the pivot is supported and turns; F the pointer attached to the
needle system, and indicating current or electro motive force on the dial H;
Ga frame carrying the coils, dial and pivot brackets, and which is fastened to the
case O by the bolts K. .
To show the direction of the current when continuous, I may place a small
magnetised needle in a convenient part of the magnetic field produced by the
current, which needle shall be so marked or fitted as to indicate deflections to
either side, and thus the direction of the current.
This magnetised needle is conveniently controlled and brought back to a middle
position by a light spring or by a bar or mass of soft iron placed near it, so as to
indicate, either by a special indication or an absence of any visible indication, that
no current is passing.
L, figures 1 and 2, is a saddle shaped piece of soft iron inside the legs of which a
small permanent magnet M is pivoted; this magnet carries a disc of paper with an
arrow marked on it, which, when a current passes through A, and the needle is
thereby deflected, so as to be parallel to the magnetic axis of the coils, shows
through an opening in the dial H, and indicates in which direction the current is
passing through the instrument. When no current is passing in A, the magnet M
is by the iron saddle L deflected back, and so brings the arrow in the paper disc
into a position at right angles to the slot in the dial and which is therefore not
seen, so showing that no current is passing through the instrument. N is a cover
to the coils, and Q a cover to the whole top of the instrument; R are connections
to the terminals T T¹.
Figures 3 and 4 are an elevation and plan of a form of my invention where a
horse shoe electro magnet is employed. A A are the coils through which the
current to be measured passes, and which excite the magnet iron J J. C is the
large and D the small needle; E is a plate of non magnetic material, carrying
the jewel hole for one end of the pivot P, the other end being carried by J, as
shown, or by a plate attached to J; F is the pointer; R the connections from the
coils to the terminals; S S₁ are pole pieces to the magnet which I sometimes omit.
It will be seen that C is further from the poles of the magnet than D, and con-
sequently in a weaker part of the magnetic field. In the figure 4 the needle
system is shown with the axis of the small needle in the line joining the two poles
of the magnet. When a current passes through the coils the needle system turns
in the direction indicated by the arrow by reason of the deflective force of the
magnetic field on C. This is, as in the case of figures 1, 2 and 5, resisted by the
force acting on D; but, as the current increases, the opposing force of D is more
and more overcome, and the pointer moves further in the direction shown.
Figures 6 and 7 show a somewhat different form of electro magnet. A is the
coil, shown diagrammatically surrounding a soft iron bar J, which is supported on
a brass bracket G. J¹ J" are soft iron bars outside the coil, and also attached to G
and carrying the pivot brackets E E'. C and D are the large and small needles,
the former being shown in two parts, joined and carried by a small brass or other
wire attached to the pivot P. F is the pointer. Assuming that a current is
passed through the coil in such a direction that the upper end of J is made a north
and the lower a south pole, the upper ends of J¹ and J¹¹ will be rendered south
and their lower ends north poles; the needle D will be caused to show north
polarity at both its ends and south polarity at its middle part, and the needle C will
have south polarity at its two extreme ends and north polarity at both the ends
near the pivot. The ends of the needles will be attracted by the poles of J¹ and Ju

page_text: "
and the motion of the pointer with increasing currents will be in the direction
indicated by the arrow. This arrangement is intended to produce an "astatic"
system, the similarity of the poles at each end of the individual needles rendering
the system less liable to be affected by outside magnetic influences.
A similar arrangement to this, but with the iron bars of the electro magnet
removed, is shown in figures 10 and 11, which are respectively a section and plan
of the apparatus. A A¹ are coils of wire or other form of conductor of an oblong
shape wound in opposite directions to one another and forming parts of the same
circuit. CC are the large needles, two being shown; D the small needle; F the
pointer, and P the pivot. The pivot P is in the magnetic axis of the coils, and the
current passing through these, magnetises the needles in such a way that the middle
of D is a north pole and its two ends south poles, while the middles of C and C
are south poles, and their ends north poles or vice versa. The shape of the coils is
such that all three needles will tend to place themselves in the position of Da
shown in figure 11; but, as the current increases, the needle system will turn
further in the direction indicated by the arrow.
It will be evident that the larger or unsaturated mass or needle of magnetic
material may be equivalently replaced by a coil of wire or other conductor carrying
the whole or part of the current to be measured, as the magnetic force of both
increases directly or very nearly directly, with the strength of the field produced
by the fixed coils or magnets. In fact it is well understood that a coil of wire
carrying a current acts in every way like a magnetised bar. In instruments where
exceeding accuracy is required, it is advantageous to replace the larger mass of iron
with a coil of wire in this way as the changes in the magnetic force of iron,
particularly when not saturated, are not always exactly proportional to the
strength of the current producing the magnetism. This coil replacing the larger
mass or needle of magnetic material may act in the various instances by attraction
or repulsion or by deflective force.
In replacing the large needle with a coil, in the cases of figures 1, 2 and 5,
I generally employ the arrangement shown diagrammatically in figure 12. A is
the fixed coil enclosing the small iron needle D, and C is the moving coil, which is
duplicated below as shown, and wound there in an opposite direction, so as to form
a figure 8; thereby the system is rendered partly "astatic." C and D are rigidly
connected together as will be well understood, and the system is suspended or
pivoted in known ways, the current entering the moving coil by mercury cups R. R.
With regard to replacing the large masses or needles of magnetic material with
coils of wire carrying a current, I find the best arrangement in figures 10 and 11,
is to use a movable coil of approximately the same form as those shown in the
figures, and to place it below the lower coil A¹ in such a position that its magnetic
axis coincides with that of the other coils. The action between the current in the
fixed coil A' and that in the moving coil would be such as to tend to set the
moving coil in a position similar to that occupied by the fixed coil.
This moving
coil and the small needle D of magnetic material are attached rigidly together, the
small needle being in a position nearly at right angles to that shown in figure 11,
when the moving coil is in the position similar to that of the fixed coils, and
therefore the tendency to motion of the coil and small needle respectively is in
opposition to each other; but as the current increases, the moving coil will more
overcome the small needle.
In figure 13, A is a coil or solenoid carrying the current to be measured, C the
large mass or rod, and D the smaller rod or wire of magnetisable material. C and D
are suitably suspended in known ways, so as to be free to move longitudinally
along the axis of the coil, one method I employ being to support the system
vertically by a fibre passing over a pulley, and having a counter-balancing weight
at its other end. Or, the interior of the solenoid may be filled with a liquid and
the moving system made of the same specific gravity as the liquid by properly pro-
portioning its form and material, it being made hollow if the liquid is lighter than
the magnetic material, or weighted with a heavier substance if the liquid is heavier.

page_text: The coils producing the magnetic field in my device may be of thick wire and
the dial will then be graduated to show the value of the current in ampères; or
they may be of thin wire of high resistance to measure electro motive force, and
the dial will then be graduated in volts in a well known manner.
In this latter case the coils will become heated by long continuance of the
current, and their resistance will be thereby altered. To remedy this irregularity
I may introduce a compensating arrangement. To effect this the pointer of the
instrument is so arranged that it is capable of turning on the spindle or some
other portion of the moving parts, and motion is communicated from these parts
to it through a spiral or other suitably shaped thermostatic band constructed in
known manner of two or more strips of different metal so as to move the pointer
on its spindle for variations of temperature in the coil. A compensation by the
movement of the pointer or of the dial by the thermostatic band for changes of
temperature may thus be made, so as to counteract the errors of the indication of
the electro motive force effected by the change of temperature of the coil.
Figures 8 and 9 show this arrangement, where Z is the thermostatic band which
would be placed close to the coil so as to quickly attain the same temperature.
This thermostatic band is attached to the pivot or one of the needles at one end,
and at the other is fixed in a pin V attached to the pointer F. The pointer is held
loosely on the pivot P between two collars as shown.
To increase the range of my instruments, I may make the relative position of
the needles and the coils or electro magnets adjustable, so that, for instance, when
the coils are moved away from the needles to a certain point, the indications of the
pointer have to be multiplied by a known constant.
To control or regulate the current I may attach to the moving parts of the
instrument a contact arm to work between two contact stops, so adjusted that
when a certain maximum or minimum limit of current passing through the coil or
coils has been reached, contact is made with one or other of these stops, whereby a
current is allowed to flow in properly arranged circuits to ring a bell, or to actuate
any other apparatus to effect any required control or result. This is shown in
figure 9, where X X³ are two adjustable contact stops, and Y a contact pin on the
pointer.
The needle systems in the various forms of my invention I carefully balance, so
that if pivots are employed, the apparatus may be used in any position. I also
sometimes use suspended instead of pivoted needle systems, arranged in well
understood ways.
In describing these forms of my invention I have not considered it necessary to
detail the means of connecting up the coils; but have confined myself to showing
clearly the nature of that which constitutes my invention.
I do not restrict myself to particularly shaped or formed conductors or magnets
producing the magnetic field used to control the moving system in my apparatus,
or to particularly constructed needles or masses of magnetic material or coils or
other conductors forming the moving and indicating system; for it is quite possible
to use other forms than those described. For instance magnetisable bars might be
so placed inside a coil or coils as to be attracted towards the sides of the coils, the
essence of my invention being maintainable through these various devices; namely,
that the magnetisable bodies or their equivalents shall act in opposition to one
another and with necessarily a different ratio of increase or decrease of magnetic
force with an increase or decrease in the electric current to be measured or
controlled.
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:-
1 The combination of two or more pieces of magnetisable material, capable of
magnetisation from the same source to a different degree, and freely sliding,
moving, or turning on a common support or axis; with a coil or coils with iron core

page_text: or otherwise surrounding or adjoining the said magnetisable bodies, and conveying
an electric current to be measured or controlled by the movement of the axis or
support of the said magnetisable bodies, resulting from the differential deflective
force, repulsion or attraction exerted by the said coil or coils on the said mag-
netisable bodies, substantially as described.
2nd The combination of a magnetisable body such as a thin soft iron needle with
a coil or coils attached thereto and equivalent to a larger mass or needle conducting
the whole or part of the electric current to be measured or controlled, the whole
freely sliding, moving or turning on a common support or axis by reason of the
differential repulsion, attraction or deflective force exerted by the said needle and
coil with respect to a fixed magnetic field produced by the fixed coil or coils
conveying the electric currents to be measured or controlled.
3rd The specific construction of such a differential instrument for measuring or
controlling electric currents, substantially as described and illustrated with reference
to figures 1 and 2.
4th The specific construction of such a differential instrument for measuring or
controlling electric currents, substantially as described and illustrated with reference
to figures 3 and 4
5th The specific construction of such a differential instrument for measuring or
controlling electric currents, substantially as described and illustrated with reference
to figures 6 and 7.
6th In such a differential measuring or controlling instrument the combination
with the indicating pointer or other parts of the apparatus of a thermostatic band
or coil to correct the reading of the said pointer for change of resistance in the
conducting coil by reason of variations of temperature, substantially as described
and illustrated with reference to figures 8 and 9.
7th The specific construction of such a differential instrument with differential
needles or an equivalent coil and needle for measuring or controlling electric
currents, substantially as described and illustrated with reference to figures 10
and 11.
8th The specific construction of such a differential instrument for measuring or
controlling electric circuits, substantially as described and illustrated with reference
to figure 12.
9th The specific construction of such a differential instrument with differential
needles or an equivalent coil and needle for measuring or controlling electric
currents, substantially as described and illustrated with reference to figure 13.
D
1
200
1
T
1000
FELL & WILDING,
Agents for the Applicant.