Improvements in or relating to Electrical Measuring or Indicating Instruments.
Year: 1891

page_text: Date of Application, 4th Apr., 1891
Complete Specification Left, 4th Jan., 1892—Accepted, 6th Feb., 1892
PROVISIONAL SPECIFICATION.
Improvements in or relating to Electrical Measuring or Indicating
Instruments.
I, ADRIAN DENMAN JONES, of 26 Gower Street, Bedford Square, in the
County of London, Electrical Engineer, do hereby declare the nature of this
invention to be as follows:-
:-
My invention relates to electrical measuring or indicating instruments, such as
ammeters, voltmeters, and the like; the object being to obtain a greater range for
the index finger, with more equal divisions of the scale, to obtain greater accuracy.
The said instruments may also be made quite portable, by suitably balancing the
parts.
in
In the ordinary method of constructing measuring or indicating instruments, the
property of an electric current to heat a wire, or to exert magnetic influence, is
made use of as a means of indicating or measuring the direction, quantity, or electro
motive force of the current. The magnetic influence of the current is most
frequently adopted for the purpose, and there are various forms and arrangements
use, based upon this principle. For example, there are instruments in which au
index finger is caused to move by the effort of a small iron bar to place itself in the
strongest part of a magnetic field, produced by the current flowing through a
surrounding coil. There are other instruments in which the magnetic effect
(similarly produced by a coil), tends to draw a piece of iron to the centre of the
interior space of the coil; and others, again, in which an iron bar, or magnetized
needle, suitably pivoted in the centre of a surrounding coil, tends to set itself in an
axial direction. In all these cases, the tendency of the iron bar, or needle, to move
from the zero position, when under the said magnetic influence, is resisted by the
force of gravity, or by a spring.
Various kinds and arrangements of springs are in use for this purpose, as is well
known; but few, if any, give entire satisfaction in practical use. The springs now
in use are generally volute, twisted, or helically formed; and they are fastened to a
fixed point at one end (usually the outward end), and arranged at the other or inner
end to exert a turning action upon an index finger. The range or angular move-
ment of the index finger is small, in most cases; and the divisions or units marked
upon the scale are necessarily close together, and lead to erroneous readings. There
is, however, a form of coiled spring in use, which gives a greater range than the
above named. The metal forming the spring is flat, and of considerable length, and
is coiled or wound in close convolutions. This is held at both ends in a straight
line, and a longitudinal strain tends to produce a turning action upon a suitably
placed index finger. With low current strength a very slight force is exerted by
the iron, and in consequence of the retarding action of the spring, or gravity, a very
slight motion of the index finger is produced. When the current strength increases,
the force exerted by the iron increases more rapidly than the retarding pull of
the controlling agent, and consequently the divisions of the scale are not uniform.
By my invention, I use a volute or coiled spring, preferably of few turns.
I attach at the inner end to an axle or arbor to which (or to the end of the spring),
is secured the index finger. The other, or outward end of the spring is connected
by suitable means to the moving part under the influence of the current, so that any
motion applied to the outward end of the spring tends to turn the index finger to a
corresponding extent. Consequently, the acting force which is to be measured is
applied (through any suitable intermediate means) to the outward extremity of the
volute spring to exert an unwinding action thereon, and thereby a corresponding
turning movement of the attached index finger, which, in travelling over a suitably
This

page_text: marked scale, indicates the value or character of the acting force. With my form,
and mode of application of the spring, the force exerted by the spring is more
nearly proportional to the 'force exerted by the iron, and therefore the divisions
of the scale are more nearly equal.
I do not confine myself to the number of turns of the volute spring, but prefer to
have as few as possible to give the required range to the index finger; nor do I
confine the application of the spring to those instruments which depend upon electro-
magnetic influence, as it may be applied to record electro-thermal, or other current
effects, if desired.
Dated this 4th day of April 1891
FAIRFAX & WETTER,
433, Strand, London, Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements in or relating to Electrical Measuring or Indicating
Instruments.
I, ADRIAN DENMAN JONES, of 26, Gower Street, Bedford Square, 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 aud by the following statement:—
My invention relates to electrical measuring or indicating instruments, each as
ainmeters, voltmeters and the like; the object in view being to obtain a greater
range for the index finger with more equal divisions of the scale; and thus obtain
greater accuracy. The said instruments may be made quite portable by suitably
balancing the parts.
In the ordinary method of constructing measuring or indicating instruments, the
property of an electric current to heat a wire, or to exert magnetic influence, is
made use of as a means of indicating or measuring the direction, quantity, or electro
motive force of the current. The magnetic influence of the current is most
frequently adopted for the purpose, and there are various forms and arrangements
based upon this principle. For example, there are instruments in which an index
finger is caused to move by the effort of a small iron bar to place itself in the
strongest part of a magnetic field, produced by the current flowing through a
surrounding coil. There are other instruments in which the magnetic effect
(similarly produced by a coil), tends to draw a piece of iron to the centre of the
interior space of the coil; and others, again, in which an iron bar, or magnetized
needle, suitably pivoted in the centre of a surrounding coil, tends to set itself in an
axial direction. In all these cases, the tendency of the iron bar, or needle, to move
from the zero position, when under the said magnetic influence, is resisted by the
force of gravity, or by a spring.
Various kinds and arrangements of springs are in use for this purpose, as is well
known; but few, if any, give entire satisfaction in practical use. The springs now
in use are generally volute, twisted, or helically formed; and they are fastened to a
fixed point at one end (usually the outward end), and arranged at the other or inner
end to exert a turning action upon an index finger. The range or angular move-
ment of the index finger is small, in most cases; and the divisions or units marked
upon the scale are necessarily close together, and lead to erroneous readings. Thero
is, however, a form of coiled spring in use, which gives a greater range than the
above named. The metal forming the spring is flat, and of considerable length, and
is coiled or wound in close helical convolutions. This is held at both ends in a straight
line, and a longitudinal strain tends to produce a turning action upon a suitably
placed index finger. With low current strength a very slight force is exerted by
the iron, and in consequence of the retarding action of the spring, or gravity, a very
slight motion of the index finger is produced. When the current strength increases

page_text: the force exerted by the iron increases more rapidly than the retarding pull of the
controlling agent, and consequently the divisions of the scale are not uniform.
By my invention, I use a volute or coiled spring, preferably of few turns. This
I attach at the inner end to an axle or arbor to which (or to the end of the spring),
is secured the index finger. The other, or outward end of the spring is connected
by suitable means to the moving part under the influence of the current, so that
any motion applied to the outward end of the spring tends to turn the index finger
to a corresponding extent. Consequently, the acting force which is to be measured
is applied (through any suitable intermediate means) to the outward extremity of
the volute spring to exert an unwinding action thereon, and thereby a corre-
sponding turning movement of the attached index finger, which, in travelling
over a suitably marked scale, indicates the value or character of the acting force.
With my form, and mode of application of the spring, the force exerted by the
spring is more nearly proportional to the force exerted by the iron, and therefore
the divisions of the scale are more nearly equal.
In the further description of this invention, reference is made to the accompanying
drawings in which
Fig. 1 is a front elevation, Fig. 2 a side elevation, and Fig. 3 is a plan of the
principal parts of an electrical measuring instrument-such as an ammeter or volt
meter.
Fig. 4 represents the dial face of a suitable scale or index for the instruments
just named.
Fig. 5 is a diagram showing a modification of the arrangement shown in
Fig. I; and
Figs. 6 and 7 are diagrams showing the application of my invention to instru-
ments in which the thermal or heating effect of electric currents are made use of.
Fig. 8 shows the form of spring I prefer, and
Fig. 9 is an elevation of a tool whereby the proper curve may be given to the
spring.
In Figs. 1, 2 and 3 the inner end of the improved volute spring a is shown
as soldered to an arbor or axle b (around which it is partially curled), carried by
suitable bearings or pivots c upon a framework d. The outer end of the spring a
is connected to the iron armature e (or other moving part acted upon by the current)
through the intervention of the connecting piece The latter may take several
forms to suit the instrument and current effect adopted, but it is preferred to attach
the outer end of the spring a to the picce in such a manner--or to form the piece f
so-that the movement will tend to uncoil the spring in a fairly straight direction,
and not to bend or break the spring. At a suitable part of the axle an index
finger g is mounted and turns with it when acted upon by the spring a. The index
finger or the armature e-or both-may be suitably counterweighted. The
ctuating current passes through the coils and acts upon the armature e to turn it,
while the zero position of the index finger g is assured by the adjustable stop screw i,
all in the well known manner. Fig. 4 is a typical index scale showing the great
auge of the finger g as acted upon by my improved spring a, and the equitable
livision of the scale; but I do not confine myself to this form or arrangement of
cale, as many different kinds are required for different instruments or purposes.
Fig. 5 is a diagram of a modification of Fig. 1, in which the armature e is acted
pon by the magnetic action of the coils h, the outer end of spring a being
ttached to the pivoted connecting piece f.
The diagram in Fig. 6 indicates a wirej stretched between fixed points k, k, and
dapted to be heated by a current. A spiral or other spring 1, also secured at one
nd to a fixed point &, is attached to the wire j and to the spring a so as to bring
he index finger g to the normal position or zero. When the current is passed
hrough the wire, and by heating it causes its expansion, the spiral spring acts to
eflect it, and at the same time to uncoil the volute spring a which produces a
orresponding movement of the index finger g.
ffect is used and adapted in like manner to uncoil the spring a, but the wire is
In the diagram Fig. 7 the thermal

page_text: stretched from the fixed point over a pulley m whose pivot or axle also
represents a fixed point to the spring a, and is shown as uncoiling the same. Both
these arrangements may be used for measuring alternating currents.
Fig. 8 represents the curvature and turns of my improved volute spring a. It is
preferably made of a thin and narrow ribbon of phosphor bronze, and the required
curvature is easily given to a straight piece of ribbon by means of the tool shown
in Fig. 9. This is conveniently made of a brass rod in the shape of a right angle
triangle, the base of which is fixed in a vice. The top or perpendicular side of the
tool is filed to the shape shown; and by pressing a ribbon flat ways against the
face formed by the top and lower sides in the direction shown by the arrow, turning
the ribbon over the top and drawing it from beneath the pressure of a finger thereon,
while holding and pushing the other end along the face of the hypothenuse, the
desired form is imparted to it.
I am aware that in many electrical measuring and indicating instruments a coiled
volute spring is used; the said spring being formed like the air spring used in
watches for working the escapement, and having many turns. Moreover, with
such springs the index finger is mounted at either the inner or the outer end, while
the other is attached to a fixed point, but I do not lay claim to any of these things.
I find, also, that the instruments made with my improved form of spring are well
adapted for mounting upon a switchboard or in other vertical positions, while
instruments made with other forms of springs that will also give a good range of
scale, require to stand with their faces in a horizontal position, and therefore their
use is limited to some extent.
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 improved volute spring of few turns attached at the outer end to a part
moveable under the influence of an electric current, and at the inner end to a
rotatable axle carrying an index finger, the said axle being placed at right angles
to the line of movement, or extension of the said spring, substantially as and for the
purpose herein shown and described.
2. In an electrical measuring or indicating instrument of the class herein described,
the combination of a volute spring of few turns, an intermediate or moving part
acted upon by the current and attached to the outer end of the said spring, a pivoted
axle or arbor attached to the inner end of the said spring and rotatable by the
coiling or uncoiling of the spring, an index finger attached to and moving with the
said axle, and a suitable wide range indicating scale, substantially as and for
the purpose herein shown and described.
3. The improved volute spring of few turns combined and arranged as indicated
in Figs. 1, 2, 3, 5, 6 and 7, and described with reference thereto.
Dated this 4th day of January 1892.
FAIRFAX & WETTER,
433, Strand, London, Agents for the Applicant.