Improvements in Electric Measuring Instruments.
Year: 1892

page_text: Date of Application, 1st Mar.. 1892-Accepted, 14th May, 1892
[Communicated from abroad by EDWARD WESTON, of Newark, New Jersey,
United States of America, Electrician.]
Improvements in Electric 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 an instrument for the measurement of current, strength
or pressure. It depends upon the principle that a wire when heated by a current
passing through it will expand, and that the extent of the expansion or elongation
hears a relation to the current, strength or pressure.
In the accompanying drawings,
Figures 1 and 2 relate to a form of instrument in which the thin wire or other
body which is expanded by the action of the current is arranged in the form of
an open loop.
Figures 3 and 4 relate to a form of instrument in which the wires are disposed
in a zig-zag arrangement, the object and purpose of which is hereinafter more
fully explained.
Figure 5 is a detailed sectional view showing the mode of connection of the wire
to the rotary arbor which carries the index needle in both forms of instrument.
Similar numbers of reference indicate like parts.
Referring first to the form of apparatus which is shown in Figs. 1 and 2, 1 is
the base of the instrument; 2 is a bracket thereon having arms 3 and 4; the
arm 4 receives a screw-step 5, the arm 3 receives a sleeve 7 provided with a head 8
by which it may be rotated in said arm; the sleeve 7 receives a screw-step 9.
Between the steps 5 and 9 is pivoted the shaft or arbor 10. Connected near one
end of said shaft 10 is the extremity of the coiled spring 11; the other end of the
spring 11 is fastened to the bent-over extremity of an arm 12, which is received
upon the sleeve 7. The torque of the spring 11 normally tends to rotate the
shaft 10, and may be increased or diminished by tightening the spring more or
less, which can be done by rotating the sleeve 7. Also supported on the arbor 10
is an index needle 13 which extends over a fixed scale 14. This scale is to be
suitably marked in electrical units as of strength or pressure. Also on the
arbor 10 is a fixed disk 15 to which is fastened the extremity of the thin filament
or wire 16. At 17, 18, 19, 20, 21, 22 and 23 are a number of posts, each carrying
a spring arm 24. The arms 24 are notched near their ends to receive the wire 16.
After passing through these notches the end of the wire 16 is attached to a fixed
stud 25 upon a plate 26 which is secured upon the base 1. A similar plate 27
also connects with the bracket 2. On the plates 26 and 27 are binding posts 28
and 29.
In the screw-steps 9 and 5 are jewels which receive the extremities of
the arbor 10. The arbor 10 is therefore insulated from its support. The circuit
in the instrument therefore proceeds as follows: From binding post 29 to arm 12,
spring 11, arbor 10 through the wire 16 to stud 25, plate 26 and binding post 28,
or vice versa. It will be noticed that the circuit is led through the coiled spring 11
so that the same spring which opposes movement of the shaft 10 leads the current
of the expansible wire 16.
When the current passes through the wire 16 said wire, becoming heated,
expands. The strain which it normally exerts upon the arbor 10 is thus relaxed,
and the spring 11 operates to turn said arbor over a distance which is determined
by the amount of elongation of the wire. As in accordance with well-known laws
the elongation of the wire depends upon the temperature to which it is raised

page_text: and as its temperature in turn depends upon the strength of the current traversing
the wire, it follows that by observing the extent of movement of the index over
the scale, have here a simple and accurate means of electrical measurement.
The springs 24, it is important to note, are practically frictionless supports, and
hence the wire does not render through the notches, but in lien thereof there is a
slight swaying of the spring on this post due to its own elasticity. I do not intend,
however, to limit myself to the particular form of support shown in Fig. 1, because
I may use instead a spring support and arm 30 having at its extremity a horizontal
roller 31 over which the wire passes. In place of a single wire, as 16, I may use
two or more such wires supported in like manner upon arms, and in this way. I may
increase the sensitiveness of the instrument.
Referring now to the form of apparatus shown in Figures 3 and 4, my object
here is to produce for very slight changes in contraction or expansion of the wire, or
other body acted upon by the current, relatively large movements of the index
needle whereby such slight changes, or even fractions thereof, may be accurately
recognized. The arrangement of the shaft 10, spring 11,.needle 13 and associated
parts is substantially the same as has already been described and as is shown in
Figure 5. Upon the baseboard of the instrument are fastened a series of metal
plates 32, 33, 34 and 35 branching one from the other substantially as shown, and
provided with binding posts 36, 37, 38, 39 and 40. These posts are to be insulated
from the plates which support them in any suitable way. 41 is one of the main
binding posts of the instrument, and this is electrically connected with the binding
post 40. Extending between the binding posts 39 and 40 is a fine filament or
wire 16. Attached to the wire 16, and at about its middle, is a shackle or link 47
which is insulated from said wire. To the shackle 47 and also to the binding
post 39 is attached a coiled insulated wire 46. Extending between the shaft 47
and the binding post 38 is a wire 16" similar to wire 16. On the wire 16" is a
shackle 45 similar to shackle 47, and between shackle 45 and binding post 38
extends a wire 44 similar to wire 46. From the shackle 45 to binding post 37
extends a wire 16 similar to 16". On the wire 16 is a shackle 43, and between
shackle 43 and binding post 37 extends a wire 42 similar to wire 44.
shackle 43 to binding post 36 extends a wire 16 similar to 16", and on wire 16" is
a shackle 48 similar to skackle 43. Extending between the shackle 48 and the
binding post 36 is a wire 49 similar to wire 42. Finally, extending from shackle 48
to the disk 15 on the shaft 10 is a wire 16. The circuit in the instrument,
therefore, proceeds as follows: From binding post 41 to binding post 40, wire 16
to binding post 39, thence to coiled wire 46, thence through the shackle 47 to
wire 16", to binding post. 38, wire 44, wire 16, binding post 37, wire 42, wire 16,
binding post 36, wire 49, wire 16, shaft 10, spring 11, arm 12, bracket 2 and
binding post 29. The effect of the spring 11 is to exert a constant strain upon the
system of wires 16", 16", 16° and 16, which strain, however, should not be normally
sufficient to draw said wires much, if at all, from a straight line. The extent of
this constant strain can of course be graduated by suitably adjusting the spring 11.
The operation of the instrument can best be understood from the diagram,
Figure 4. Assuming the current first to pass to the wire 16 it produces an
expansion of that wire, but this wire 16 is subjected to the pull of the wire 16"
laterally applied. Now as may be shown by a simple trigonometrical demonstra-
tion, the extent of displacement of the middle point 47 of the wire 16 under these
conditions is considerably more than the extent of elongation of the wire due to
this expansion, so that if I should connect the wire 16 directly to the shaft 10.I
could by the aid of a single wire produce an index movement which would be
greater than the actual elongation of the wire measured longitudinally, but my
object is to produce a very large index movement, and therefore I use a series of
wires 16, 16, 16", etc. The effect upon the wire 16, strained as it is between the
fixed points 39 and 40 and subjected to the pull of the wire 16", is to cause a
displacement of the middle or shackle of the wire 16 as I have already stated,
but the effect of moving the point of attachment 47 of the wire 16* will obviously
From

page_text: result in a still greater displacement of the middle point of the wire 16, and the
extent of this displacement is further augmented by the individual expansion of
the wire 16" due to the current which traverses it. The same state of affairs is
repeated in the wires 16" and 16%, so that finally, as is shown in Figure 4, a very
large displacement of the shackle 48 or middle point of the wire 16 occurs. As
the wires yield because of the elongation before noted, the wire 16 is wound upon
the shaft 10 by the action of the spring 11, but the revolution of the shaft 10 also
moves the needle 13 over the scale 14, so that as will be apparent, for a very small
increase in the wire 16, or even for the sum of the small increments of expansion
occurring in all the wires due to the action of the current traversing them, a very
large are of movement of the needle 13 results. It is of course not necessary that
the current should pass through all the wires 16; 16", etc., because a displacement
of the first wire 16 due to the passage of the current through it, only would become
enormously magnified when the wire 16 is reached; but by passing the current
through all the wires I get, first, a greater arrangement of movement of the
index, and second, a greater sensitiveness of the apparatus.
The advantages of the two forms of instrument which I have now described are
as follows-Referring first to the type of instrument illustrated in Figures 1 and 2,
its construction is cheap and simple, it is without multiplying gear, the wire may
rest upon frictionless supports and hence be under no tension other than the spring
exerts, which of course is no more than is necessary to take up the slack as the
wire expands. The wire can be made of the diameter of one-thousandth of an
inch; the usual diameter of wire in expanded volt meters is 31 one-thousandthis
of an inch, therefore the last-named apparatus requires over nine times as much
current as mine does. I may make the base of metal, and of such form and
dimensions that its expansion due to atmospheric changes shall correspond to that
of the wire and thus render the instrument independent of such variation. The
portability of the instrument will be obvious.
Referring to the form of apparatus illustrated in Figures 2 and 4, not only do I
get a very large range of index movement but also, as in the case of the instrument
illustrated in Figures 1 and 2, I am not obliged to heat my wires to high
temperatures in order to get such range. This is one of the great difficulties in
all classes of measuring instruments which depend upon the expansion of wires
heated by the current. The constant heating and cooling of the wire not only
destroys it but produces permanent set, which in time renders the instrument
inaccurate. I find that in practice I need not use a temperature exceeding
100 degrees centigrade, and it is obvious that the strength of the current need be
but very small.
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 operated by the expansion or contraction
of a fine filament or wire in circuit, the said wire being arranged in loop form upon
suitable supports and having one end attached to a fixed, and the other to a
movable abutment, the said movable abutment controlling an indicating device.
2. An electrical measuring instrument operated by the contraction and expansion
of a fine filament or wire arranged in loop form upon supports, one end of said
wire being connected to a fixed abutment, and the other to a rotary arbor provided
with a spring which normally tends to cause said arbor to produce tension of said
wire, the circuit connections being arranged so that the current is led through said
spring to said expansible wire.
3. An electrical measuring instrument containing a flexible body of conducting
material extending between abutments, means for subjecting said flexible body to
the action of electricity, a second flexible body maintained in a set of tension,
connected to a point of said body and extending at an angle thereto, and an
indicating device controlled by said second flexible body.

page_text: 4. An electrical measuring instrument containing a series of wires which may be
elongated or expanded by a current passing through them, and connected in series
one to the other, substantially as described, in combination with a means of sub-
jecting said wires to tension, and an indicating device for showing the extent of
displacement or expansion of said wires due to the passage of the current.
Dated this 1st day of March 1892.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.