Improvements in Electrical Measuring Instruments.
Year: 1892

page_text: Date of Application, 8th June, 1892-Accepted, 9th July, 1892
COMPLETE SPECIFICATION.
[Communicated from abroad by EDWARD WESTON, of Newark, New Jersey,
United States of America, Electrician.]
Improvements in Electrical Measuring Instruments.
I, HENRY HARRIS LAKE of the firm of Haseltine, Lake & Co. Patent Agents,
45 Southampton Buildings in the County of Middlesex 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:-
The invention relates to that class of electrical measuring instruments in which
a coil, supported and vibrating in a field of force, is caused, by the passage of a
current through it, to move over to an angular distance depending upon difference
of potential between the instrument terminals.
Fig. 1 is a vertical section of the instrument on the line of Fig. 2.
Fig. 2 is a plan and partial section of the instrument, the chamber containing
the index and scale being divided on the line y y of Fig. 1.
Fig. 3 is a section of the coil support on the line
of Fig. 1.
Fig. 4 is a detail view showing the case which encloses the index in vertical
section on the line a¹¹, Fig. 1.
Figs. 6 and 7 are enlarged views of the device for increasing the needle
deflections, Fig. 7 showing the device in front view, and Fig. 6 in side view and
partial section.
Fig. 5 is a modification of the device shown in Figs. 6 and 7, similar numbers
indicating like parts.
Referring first to Figs. 1, 2, 3 and 4, in the base 1 of the instrument is a
recess 2 to receive the circular iron plate 3, having the flange 4. 5 is a plate
similar to 3, having flange 6. The plates 3 and 5 and the metal ring 7 form a
closed circular case, in which is a fixed coil 8 of insulated wire. The opposing
faces of the iron pole pieces 9 and 10 are made concave. On their sides are
caps, 11.
Also on the pole pieces are bars, 12 and 13, which carry a solid iron
cylinder 15. Surrounding the cylinder 15 is a coil, 16, pivoted in jewels, 17, in
the caps 11. On cap 11 is a collar 18, which carries an arm 19, to which arm is
fastened one end of a spiral spring 20. The other end of spring 20 is secured to
pivot shaft 21, which also carries an index needle 22. This needle extends up
through a slot 24 in the upper disk 5 and enters a closed case 23.
In the rear
wall of said case is an opening, Fig. 4, in which is secured a plate 25 of white
or opal glass. On this plate of glass is inscribed a scale-marking graduated in
any suitable electrical units. In the front wall of the case 23 is placed a piece
of clear glass, 26, through which the scale can be seen. In rear of the scale-
plate 25 is any source of illumination, such as an electric lamp, 27. There are
two springs 20, two caps 11 and two rotary arms 19. When the arms 19 are rotated,
the springs 20 are more or less wound up.
The circuit in the instrument shown in Figs. 1 and 2 is as follows:-From the
binding post 28 through the fixed coil 8 to the binding post 29. The shunt
circuit proceeds from the binding post 28 to one arm, as 19, to the spring 20,
shaft 21, through the coil 16 to the shaft 21 again, opposite spring 20 and arm
similar to arm 19 thereto connected, and finally to the binding post 29. The
movable coil 16 and the fixed coil 8 are therefore in the present instrument in
multiple arc connection. When the current traverses the instrument, the movable
coil 16, in accordance with well-known laws, will set itself in a new angular
position, and its extent of movement will depend upon the difference of potential
017

page_text: between the binding posts 28 and 29. As the instrument is here shown constructed
with the coil connected in multiple are, it is adapted for use as an ammeter, and
the extent of movement of the movable coil 16 will bear a relation to the strength
of the current passing through the instrument, and hence the needle 22 supported
on the coil shaft 21 and hence actuated by the movable coil will show the current
strength on the scale 25, which may be marked in amperes.
The fixed coil 8 and the plates 3 and 5 constitute an electro-magnet of which 9
and 10 are the poles; and, by reason of the close proximation of these poles,
there will be a powerful field of force between them. The pole pieces 9 and 10
are, in fact, the core of the electro-magnet, and are therefore subjected to double
magnetic effect. The coil is completely enclosed in a shell of magnetic material,
which, in accordance with well-known laws, completely shields the parts within
from the influence of external fields of force. The slot 24 through which needle 22
passes is hermetically closed by means of the case 23, so that every working part
of the instrument is not only screened from outside magnetic effects, but is also
protected from the entrance of dust. The cylinder 15 is also a core of the electro-
magnet, and serves to gather the lines of force so as to intensify the field in which
the coil moves.
Referring now to the device shown in Figs. 5, 6 and 7, these figures show sub-
stantially the same arrangement of needle supporting shaft, spring and rotary
arms as is shown in Fig. 1. The shaft 21 is here shown arranged in a fixed
bearing which is surrounded by the collar 18 which carries the arm 19, the end of
which is fastened to the end of the spiral spring 20. When the shaft 21 is rotated
by any means, as, for example, by the coil 16 in Fig. 1, its movement will be
opposed by the uniform resistance of the spring 20; so that, if, for a given force,
the needle move from zero to 1 on the scale a second application of the same force
will move it from 1 to 2, and thus the needle will pass over equal scale increments
for equal additions of force. In this case it is assumed that the spring 20 exerts no
rotary action on the shaft when the needle is at zero.
Suppose it now to be desired that for each force increment above noted, a large
deflection of the needle should be produced; such, for example, as from zero to 2,
instead of from zero to 1. I can accomplish this obviously by substituting for the
spring 20 another spring of less resistance; but in that case, under the same con-
ditions I shall have greatly diminished the measuring capacity of the instrument.
Thus, if as shown in Fig. 7, I can measure from zero to 10 amperes, for example,
after the substitution of the spring, I can only measure from zero to 5.
In many cases, it is desirable to produce this large deflection of the needle for
force increments beyond a certain point. Thus, it is often necessary to measure
amperes after a certain strength has been obtained; as, for example, between 5
and 10 amperes.
In such case, it is not necessary that there should be a reading
on the instrument between zero and amperes, and the initial point may be the
5 ampere point. What, therefore, is wanted, is a large deflection of the needle for
each ampere between 5 and 10 amperes, for example. This I accomplish by
moving the arm 19 so as to wind up the spring and to force the needle against the
stop 30 with such a force that, in order to overcome its resistance and to cause it
to move away from said stop a force of more than 5 amperes must be exerted.
soon as the needle thus arranged is overbalanced, then its deflection will depend
upon the resistance of the spring; and if, as already stated, the resistance of the
spring is made so small as that the needle may move from zero to 2 for each
additional force increment, then, clearly, for all increments between the limits fixed,
the needle will give the desired large deflection.
As
In the device shown in Fig. 5, a weight, 32, suspended by a cord from the
pulley 31 on the shaft 21 is substituted for the spring 20. In this case, the
magnitude of the weight corresponds to the resistance of the spring produced by
winding it; and therefore, this magnitude is to be adjusted to afford the necessary
initial opposition to the movement of the needle.

page_text: Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed as communicated to me by
my foreign correspondent I declare that what I claim is :-
1. An electrical measuring instrument comprising a fixed coil, an internal core
having its polar extremities facing and opposite, a movable coil supported and
vibrating between the poles of said core, and a body of magnetic material supported
within said coil, the construction being such that an intense field of force is pro-
duced in the space between said poles and the inner core, in which space said
movable coil operates.
2. An electrical measuring instrument constructed substantially as herein
described, provided with a translucent scale and an index or pointer moving over
said scale.
3. An electrical measuring instrument having a fixed coil and a movable coil
arranged substantially as herein set forth, and provided with a case enclosing the
working parts and forming a magnetic shell to screen said parts from exterior
inductive influences.
4. An electrical measuring instrument containing a spring or other elastic body,
a device for subjecting said body to strain against its own elasticity, an index con-
trolled by said body, and a stop for preventing movement of said index due to the
initial strain, and mechanism controlled by the current in the instrument and
operating to actuate the index; the whole forming a device for causing relatively
large deflections of the index of the instrument corresponding to force increments
applied thereto.
Dated this 8th day of June 1892
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.