Improvements in Electrical Measuring Instruments.
Year: 1890

page_text: Date of Application, 29th Apr., 1890-Accepted, 28th June, 1890
COMPLETE SPECIFICATION.
[Communicated from abroad by EDWARD WESTON, of Neward, New Jersey, United
States of America, Electrician.]
Improvements in Electrical Measuring Instruments.
I, HENRY HARRIS LAKE of the firm of Haseltino Lake & Co., Patent Agents
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 an instrument designed for the measurement of the
pressure or strength of electrical currents. It embodies broadly a coil of wire pivoted
in the field of a magnet, and carrying an index needle which moves over a suitable
scale. The coil assumes an angular position depending upon the difference in
potential of the current at the binding posts of the instrument and the deflection of
the needle over the suitably marked scale indicates said difference in volts.
The principal novel features embodied are the use of oppositely acting springs in
combination with the rotating coil, the construction of said springs of non-inductive
or non-magnetic material, the devices for tightening or loosening said springs, the
guard to prevent catching of the inner turns of said springs over the outer abutments,
the arrangement of the scale plate and its support on the pole pieces instead of on the
magnet, the construction of said plate and combination therewith of the mirror, the
uniting together of the pole pieces, coil and scale plate, so that these parts may be
separated as a unit from the magnet, the construction and arrangement of the con-
centric resistance coils, the novel form of circuit closer, and the disposition of the
circuit connections together with other combinations and instrumentalities, all as
hereinafter more particularly set forth.
In the accompanying drawings,
Fig. 1 is a plan view of the instrument with the case or cover removed.
Fig. 2 is a section on the line X X of Fig. 1.
Fig. 3 is a plan view showing the working parts of the instrument detached from
the permanent magnet and displaced in position so as to exhibit the separation of all
the working portions as a unit from said permanent magnet.
Fig. 4 is a rear view of the scale plate."
Fig. 5 is a section on the line Y Y Fig. 1.
Fig. 6 is a section on the line Z Z of Fig. 5.
Fig. 7 is a perspective view showing more particularly the reversely-wound springs,
Fig. S is a section on the line X'X' of Fig. 1, and
Fig. 9 is an enlarged partial section on line XX of Fig. 1.
Similar numbers and letters of reference indicate like parts.
1 is the base board of the instrument to which the permanent magnet 2 is secured
by screws (dotted circles 3, Fig. 1). On the under side of the base board 1, is a
cover 4. 5 and 6 are two pole pieces having their opposing faces hollowed to form a
cylindrical opening between them, and connected by a plate 7 of non-inductive
material by screws 8. Through the middle portion 9 of plate 7, pass screws 10, which
support a cylindrical mass 11 of iron, in the space between the pole pieces. Supported
upon the pole pieces are covers 12 and 13, through the centers of which pass
bushings 14, Fig. 9, having jewels which form bearings for the pivot pins 15. Pins 15
are secured to the copper frame 16, which surrounds the cylinder 11, and moves in
the annular space between said cylinder 11 and the pole pieces 5 and 6. Around the
frame 16 is wound a coil of insulated wire with its terminals connected to the
pivots 15. Upon said pivots 15, are fixed collars 17, to which collars are secured
the ends of coiled springs 18 and 19, of non-magnetic material, such as platinum-

page_text: iridium alloy, and wound in opposite directions, as shown in Fig. 7. The object of
making the springs of non-magnetic material is, to prevent the effects of magnetic
induction upon them, and the purpose of winding them in opposite directions is, first,
to prevent changes in the position of the needle arising from variations in temperature
acting upon the springs, thus avoiding disturbance of the position of the zero point,
which otherwise would follow from changes in the temperature of the instrument
second, to render their resilient resistance more uniform, to movement of the coil
either way, and third, to allow of delicate adjustment of the needle. Their outer
extremities are fastened to arms 20. These arms are pivoted upon the bushings 14,
but are insulated therefrom by interposed sleeves 21 of insulating material. The
springs 18 and 19 are fastened to the bent extremities of the arms 20, and said
extremities are then turned and bent at right angles, as shown at 22. The object of
thus forming the extremities of the pivoted arms 20, is to prevent any turns of the
springs when the instrument is inverted or shaken, from being caught over the end
of the arm, the bent portion 22 acting as a guard for this purpose. The object of
pivoting the arms 20 is to allow them to be rotated, and so to tighten or loosen the
coils of the springs. In this way, the opposition offered by the springs to the move-
ment of the coil of the instrument, may be nicely regulated. In each cap or cover 12
or 13 is made a slit or opening 23, which comes directly opposite the springs 18
and 19. The object of these openings is to allow an edge view of the springs 18
and 19, so that it may be seen that all the turns of each spring lie in the same plane,
and that there is no distortion of the spring. Secured to the pole pieces 5 and 6, is a
plate 24 having a horizontal portion 25, from which depends a rod 26, which receives
three concentric resistance coils, 27, 28, 29. I may increase or diminish the number
of said coils. The purpose of using several coils is to allow of each being indepen-
dently made and adjusted to any desired resistance, and all afterward being connected
together. These coils are secured upon the rod 26 by the nut 30. On the upper side
of the plate 25, is fastened a scale plate 31, Fig. 4, made of sheet metal, and provided
with stiffening ribs 32, and with three diagonally disposed openings 33, 34, 35. The
opening 35 receives a rectangular diagonally placed projection 36 on the plate 25, and
has a slight play thereon. Slots 33 and 34 receive the screws 37, by which the scale-
plate 31 is fastened to the plate 25. In the body of the plate 31 is a curved open-
ing 38, and on the under side of said plate is a mirror 39 which is seen through said
opening. The mirror is secured in place upon the plate 31 by clips 40, which are here
formed integrally from the metal plate itself. Entering on one side of the plate 7, is
a projection 41, through which pass two screws 42, 43. These screws hear against
one end of the permanent magnet 2. The two pole pieces are held between the arms of
the magnet by the pivot screws 44, which pass through the arms of the magnet, and
which bear upon the outer faces of the pole pieces. By simply loosening the screws 44,
all the working parts of the instrument being united, may be slid out of place from
between the arms of the magnet, as indicated in Fig. 3. The object of the pro-
jection 41 and adjusting screws 42 and 43 therein, is to furnish a convenient means of
leveling the scale-plate. It will be apparent, that the connected pole pieces 5 and 6
turn on the screws 44 as pivots, and that the screw 42 is above the pivot points, and
that the screw 43 is below the same. It follows, therefore, that if the screw 42 be
turned inward, and the screw 43 be turned outward, then the scale-plate will be slightly
depressed; whereas if the screw 43 be turned inward, and the screw 42 outward, then
the scale plate will be slightly raised. In this way the scale plate may be adjusted
level with nicety. The object of the slots 33, 34, 35, by means of which the scale
plate may be moved slightly in the direction parallel to the radial line passing through
the zero mark, is to allow an adjustment of the scale in length to be made without
altering or disturbing the coil of the instrument. In this way small errors of cali-
bration may be corrected. The index needle of the instrument is shown at 45, and is
fastened to a thin disk 46 on the upper pivot pin 15. It extends over the scale
plate 31. Near its extremity, it takes the form of a flat bar on edge, as shown at 47.
The object of the mirror 39 is to allow the reflected image of the. needle therein to be

page_text: brought directly under the position of the needle, so as to obviate any error due to the
parallax in observing the scalo reading. To the base board 1, and directly under the
opening which receives the lower cap 13 and arm 20, is secured a cover 48 to prevent.
access of dust to the working portion. The entire instrument is covered by a case 49,.
in which there is an opening 50 provided with glass through which the scale and
needle can be seen, and another opening 51, also covered with glass, through which
the position of the upper adjusting arm 20 may be observed.
Referring now to Figs. 5 and 6, in a recess in the lower side of the base board 1, is
secured a contact spring 52, having a contact point 53. To the binding post A of
the instrument, is also secured a contact spring 54. 55 is a push-button of rubber or
other insulating material, from the side of which project stops 56, which normally
enter recesses in a sleeve 57 in the base board 1, as shown in Fig. 6. The spring 52
normally holds the stops 56 in the upper portion of the recesses in the sleeve 57, 50.
that the contact point 53 does not then meet the spring plate 54. When the pin 55.
is pushed down, the contact point 53 meets the plate 54, and this contact may be.
maintained by holding the pin 55, as long as may be desired, depressed. Or, inas-
much as the stops 56 then leave the recesses in the sleeve 57, it is necessary simply to
turn the pin 55 on its axis, when the stops 56 will catch under the lower edge of the
sleeve 57, and the pin 55 will thus be maintained in its lowest position, and the con--
tact point 53 held against the spring 54, and the circuit will thus be kept permanently
closed.
The circuit in the instrument proceeds as follows: From the binding post A to the-
contact springs 52 and 54, by wire c to the lower pivoted arm 20, spring 19, lower-
pivot pin 15, the coil of the instrument, upper pivot pin 15, spring 18, upper arm 20,
and thence by the wire a to the binding post B. A branch wire 6 leads from the.
upper arm 20 to the resistance coil 29, (these coils being connected in series,) and to
binding post C. When the current passes between binding post A and binding
post C, it proceeds through the resistance coils, and when it passes between binding
post A and binding post B, it does not pass through said coils. In operation the
pivoted coil assumes an angular position depending upon the difference in potential of
the current at the binding posts of the instrument; and hence the deflection of the
needle attached to said coil indicates on the scale (which may be suitably in volts).
said difference of potential.
Having now particularly described and ascertained the nature of my said invention
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 embodying a magnet or other means of pro-
ducing a field of force, an electrical conductor in coil or loop form supported and
vibrating in the field of force of said magnet, and a spring of non-magnetic material
interposed between said coil and an abutment.
2. In an electrical measuring instrument, a body movable under the influence of an.
electric current, and two resilient bodies interposed between said movable body and
abutments and respectively opposing the motion of said movable body in relatively
different directions.
3. In an electrical measuring instrument, a magnet, an electrical conductor in coil
or loop form supported and vibrating upon axial pivots in the field of force of said
magnet, and two spiral springs wound in opposite directions and having their inner
ends connected to said pivots and their outer ends to abutments, and means for
varying the resiliency of said springs.
4. In an electrical measuring instrument, a magnet, an electrical conductor in.
coil or loop form supported and vibrating in the field of force of said magnet, an
abutment and a spiral spring interposed between said coil and said abutment, and.
circuit connections whereby said coil and spring are brought into electrical.
irauit

page_text: 5. The construction and arrangement of the pole pieces, coil, index and scale-plate,
whereby said parts are rendered detachable as a unit from the magnet, as hereinbefore
specified.
6. The construction and arrangement of the fixed resistance coils in combination
with the vibrating coil of the instrument, as hereinbefore specified.
7. An electrical measuring instrument constructed and arranged substantially as
herein before specified.
Dated this 29th day of April 1890.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.