IMPROVEMENTS IN APPARATUS FOR MEASURING OR INDICATING ELECTRIC CURRENTS
Year: 1882

page_text: LETTERS PATENT to James Blyth, M.A. Professor of Mathematics and Natural
Philosophy in Anderson's College, Glasgow, in the County of Lanark, North
Britain, for an Invention of "IMPROVEMENTS IN APPARATUS FOR MEASURING
OR INDICATING ELECTRIC CURRENTS
"
PROVISIONAL SPECIFICATION left by the said James Blyth at the Office of
the Commissioners of Patents on the 29th November 1882.
JAMES BLYTH, M.A. Professor of Mathematics and Natural Philosophy in
Anderson's College, Glasgow, in the County of Lanark, North Britain, "IMPROVE-
MENTS IN APPARATUS FOR MEASURING OR INDICATING ELECTRIC CURRENTS
37
This Invention has for its object the providing of improved simple convenient
and reliable apparatus for measuring electric currents.
One arrangement or application of the apparatus is designed to show in amperes
marked on a scale the quantity of an electric current flowing through a closed
circuit, and comprises a solenoid the coils of which form part of the circuit, and an
iron core, the core being attached to one end of a spiral spring which has its other
end adjustably fixed. The solenoid and core are by preference placed vertically the
core being suspended by the spring, and horizontal pointers are fixed at or beyond
the ends of the spring. The upper pointer moves over a scale marked to show
amperes; and whenever an observation is to be taken the screw or other part
bolding the spring must be adjusted so that the lower pointer will coincide with a
mark provided to insure the core being always in one particular position relatively
to the solenoid when an observation is being taken. To obtain this adjustment
with different currents it will be found that the spring will be elongated to
different extents corresponding with the differences in the currents and the upper
pointer will show on the scale the different elongations and will thus indicate the
amperes or whatever measures are marked on the scale.
An analogous arrangement or application of the apparatus is designed for showing
the difference of potential between any two points of an electric circuit through

page_text: which a current is flowing. For this purpose the solenoid is made with numerous
coils of fine copper, silver, german-silver, or other suitable wire so as to have a high
resistance; and this solenoid may be made part of a shunt loop from the main
circuit. The core and spring may be arranged as in the first application, the scale
being marked to show the difference of potential in volts.
The various parts of the apparatus are susceptible of modification. Thus the
solenoid may be wound upon a tube of soft iron. The core which is by preference
of soft iron may be solid or hollow, and in the form of a cylinder, or sphere, or of
a pair of cones joined base to base, or of any other suitable form. The iron core
may have a solenoid coil upon it with the current that is to be measured or another
current passing through it, or the core may consist of a movable solenoid without
an iron part. Any suitable form of spring may be used but a spiral metal spring
is preferable; or instead of a spring a steelyard or other weighing appliance may
be substituted, the parts being put in equilibrio with the core in its proper position,
when an observation is to be taken, either by adjusting a weight or connection, or
by putting on or taking off weights.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said James Blyth in the Great Seal Patent Office on the 28th May
1883.
JAMES BLYTH, M.A. Professor of Mathematics and Natural Philosophy in
Anderson's College, Glasgow, in the County of Lanark, North Britain "IMPROVE-
MENTS IN APPARATUS FOR MEASURING OR INDICATING ELECTRIC CURRENTS"
My said Invention has for its object the providing of improved, simple,
convenient, and reliable apparatus for measuring or indicating electric currents.
One arrangement or application of my apparatus is designed to show in amperes
marked on a scale what electric current is flowing through a closed circuit to which
the instrument is applied, and comprises a solenoid the coils of which form part of
the circuit, and an iron core, the core being attached to one end of a helical metal
spring which has its other end adjustably fixed. When an electric current passes
through the solenoid coils it gives rise to a force tending to pull the core into the
solenoid, and when the spring is adjusted so that its tension balances the pulling
force the amount of extension required for that purpose is a measure or indication
of the electric current. The instrument is fitted with appliances for adjusting the
spring and with a scale on which to read the indications obtained, such scale being
marked with amperes to directly show the current, or with millimetres or other
measures from which amperes may be calculated. Or a table may be calculated to
show millimetres or other measures and the corresponding amperes.
An analogous arrangement or application of my apparatus is designed for
showing the difference of potential between any two points of an electric circuit
through which a current is flowing. For this purpose the solenoid is made with
numerous coils of fine copper, silver, german-silver, or other suitable wire so as to
have a high resistance; and this solenoid may be made part of a shunt loop from
the main circuit. The core and spring may be arranged as in the first application,
the scale being marked to show the difference of potential in volts, or a weight may
be arranged to act in place of the spring.
The various parts of the apparatus are susceptible of modification. Thus the
solenoid coils may be wound upon a tube of soft iron. The core, which is by
preference of soft iron may be solid or hollow, and in the form of a cylinder, or
sphere, or of a pair of cones joined base to base, or of any other suitable form.
The iron core may have a solenoid coil upon it with the current that is to be
measured or another current passing through it; or the core may consist of a
movable solenoid without an iron part. Any suitable form of spring may be used
but a helical or spiral metal spring is preferable: or instead of a spring a steelyard
or other weighing appliance may be substituted, the parts being put in equilibrio
with the core in its proper or zero position, when an observation is to be taken,
either by adjusting a weight or connection or by putting on or taking off
weights.
And in order that my said Invention and the manner of performing the same
may be properly understood I hereunto append a sheet of explanatory drawings
to be hereinafter referred to and representing two modifications of my improved
apparatus.
Fig. 1. on the accompanying sheet of drawings is an elevation and Fig. 2, is a
vertical section of a modification which I have designated as a solenoid galvano-
meter. Fig. 3. is a vertical section of a simplified modification suitable for cursory
observations to be made when the indication is not required to be minutely
accurate, and which I term a current indicator. In these drawings the same
reference numerals are used to mark the same or like parts wherever they are
repeated.

page_text: In the solenoid galvanometer or apparatus shown in Figs. 1 and 2 a solenoid or
hollow cylindrical coil, 4, of insulated wire by preference enclosed in a brass case, 5,
is fixed with its axis vertical upon a base, 6, of wood which is fitted with levelling
screws, 7, and with a spirit level, 8, A hollow core 9, consisting of a thin tube of
soft iron is suspended with its axis coincident with that of the solenoid, 4, and
with its lower part within the solenoid. The core 9, is suspended at the lower end
of a helical or spiral metal spring, 10, the upper end of which is attached to the
top of a tube, 11, fitted to slide vertically in an outer tube, 12, fixed to the top of
the solenoid case, 5, The attachment of the upper end of the spring 10, to the top
of its tube, 11, is by means of a screw spindle, 13, and a pair of screw nuts, 14,
this construction being for the purpose of adjusting the position of the core, 9, to
agree with the zero of the scale when no current is passing through the solenoid.
The inner or spring tube, 11, is formed or provided with a series of rack teeth, 15,
which project into or through a groove or slot in the outer fixed tube, 12, and with
these rack teeth there gears a pinion, 16, held in a bearing on the fixed tube, 12,
the spindle of the pinion having on it a head or button for turning it by. At the
lower part of the fixed tube, 12, there is a sight hole, 17, having a fine wire across
its middle (or points projecting from each side may be used without the cross
wire.) On the core, 9, two fine horizontal lines, 18, are drawn in black on a white
ground and when the core has been adjusted in its zero positition without any
current passing through the solenoid, and with the spring tube, 11, also in its zero
position, the fine cross wire or the two points of the sight hole, 17, should be
exactly between the two lines 18, on the core, 9. A scale, 19, is fixed on the fixed
tube, 12, on the same side as the sight hole 17, and a vernier, 20, fixed on the
inner or spring tube, 11, works in a slot in the outer fixed tube, 12, to show by its
position relatively to the scale, 19, the indications the instrument is intended to
give. A socket, 21, is provided on the solenoid case, 5, in which to place a lens, 22,
as shown in Fig 1, for viewing the position of the core, 9, through the sight
hole, 17; or where more convenient an inclined mirror, 23, may be fixed in the
socket, 21, which to an observer looking downwards will show both the sight
hole, 17, and the scale, 19.
The ends of the wire of the solenoid 4, are connected to terminals 24; and
when an observation is to be taken the wires conveying the current are connected
to these terminals in such a manner that the current will, when passing through
the solenoid, 4, tend to draw down the core, 9. Then whilst the current is passing
the pinion, 16, is turned by hand so as to raise the spring, 10, until the core, 9, is
restored to its zero position, and the vernier 20, will show on the scale, 19, the
extent to which the spring is elongated in consequence of the pulling down action
due to the electric current. The tension of the spring which balances the downward
pull will correspond to the elongation, and the position of the vernier on the scale
will accurately show what current is passing.
The scale may be graduated to show amperes, or a table may be constructed to
show amperes corresponding to millimetres or other measures on the scale, by
means of apparatus arranged to effect the electrolysis of water, or by means of any
other suitable apparatus by which currents of different definite strengths can be
passed through the instrument.
In the current indicator shown in Fig 3, the solenoid, 4, is represented as
consisting of a single volute or coil of insulated copper ribbon enclosed in a case, 5,
fixed to a wooden base, 6, and having the ends of the ribbon connected to
terminals, .24. A semicircular frame, 25, with a graduated dial is fixed upon the
solenoid case, 5; and above the centre of the solenoid there is supported on pivots
a piece of soft iron, 26, or it may be a small permanent magnet. When using a
piece of soft iron it is pivotted adjacent to one of its ends and is provided with a
projecting or depending counterpoise, or there may be added to one end of the soft
iron piece a counterpoise, 26*, of brass, the combined piece being pivotted centrally
of its length. When using a permanent magnet it is pivotted centrally of its
length. A pointer, 27, is fixed to the iron piece or magnet, 26, which has also

page_text: fixed to it below its centre a brass weight, 28, to counterbalance the pulling down
force which an electric current exerts on the free end of the piece of soft iron, or ou
one or other of the ends of the magnet 26, There may be used two such pieces of
soft iron pivotted so that their pointers will move in opposite directions over
different segments of the dial. This instrument will indicate what is understood
as the direction of an electric current as well as its strength.
It is a distinguishing feature of the modifications shown in the accompanying
drawings and herein before described and of other modifications of my improved
apparatus that the force acting in either direction along or parallel to the axis of a
solenoid whenever an electric current passes through the coils of the solenoid is
availed of for obtaining an indication or measurement of the current.
Various expedients may be used for practically increasing the range of my
solenoid galvanometer or other modifications of my improved apparatus. Thus the
solenoid (4) may be composed of several separate coils and switches or terminals
may be provided by means of which the current to be observed may be passed
through one or more of the coils according to its strength. Or a number of coils
or equivalent pieces having each exactly the same resistance as the solenoid of the
instrument may be provided and the current may be passed by means of shunts
through one or more of these resistance pieces when it is stronger than what the
instrument is constructed for, the resulting indication being multiplied by 2, 3, or
a larger number accordingly.
Having thus particularly described my said Invention and the manner of
performing the same I have to state that I do not restrict myself to the precise
details herein described or delineated but that what I believe to be novel and
original and claim as the Invention secured to me by and in terms of the herein-
before in part recited Letters Patent is :-
1-The combining of a solenoid with a movable iron core or equivalent movable
piece, and with an indicating device showing the action on the movable piece in
either direction along or parallel to the axis of the solenoid of the force produced
by the passage of an electric current through the solenoid substantially as and for
the purposes herein before described.
2. The combination of parts herein before described with reference to Figures 1
and 2 of the accompanying drawings.
3. The combination of parts hereinbefore described with reference to Figure 3 of
the accompanying drawings.
4. The combination of a spring or of a weight or weights with adjusting
appliances for counterbalancing and indicating or measuring the force exerted on
an iron core or equivalent piece by an electric current passing through a
solenoid, the parts being arranged and operating substantially as herein before
described.
In Witness whereof, I the said James Blyth, have hereunto set my hand
and seal, this twenty sixth day of May, in the year of our Lord, one
thousand eight hundred, and eighty two. [sic]