Improvements in Measuring and Recording Instruments for Electric Currents.
Year: 1893

page_text: Date of Application, 10th Jan., 1893-Accepted, 28th Oct., 1893
[Communicated from abroad by EDWARD WESTON, of Newark, New Jersey,
United States of America, Electrician.]
Improvements in Measuring and Recording Instruments for Electric
Currents.
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 consists in an electrical measuring instrument which may be
arranged as either a voltmeter for measuring electrical pressure or an ammeter
for measuring current strength. The construction is such that the variations
in electromotive force or pressure are registered upon a moving record surface.
In the drawings,
Figs. 1 and 2 are illustrative diagrams, Figs. 3 and 4 are skeleton electrical
diagrams showing the arrangements of the circuits and Figs. 5 and 6 show also the
construction of the apparatus in fuller mechanical detail.
Similar letters of reference indicate like parts.
Figs. 1, 3 and 5 relate to the arrangement of the instrument as a recording
ammeter, and Figs. 2, 4 and 6 to its arrangement as a recording voltmeter.
Referring first to Fig. 1, A is a conducting body, B a pivoted finger moving
along said body. Assume the resistance of A to be 10 ohms, that of the shunt CB
to be 1 ohm and that the strength of the current is 10 amperes. Then the fall of
potential between the points a b on body A will be 100 volts, the finger B being in
the position indicated by dotted lines. Assume the strength of the current in the
part db of the body A to increase to 100 amperes. Then if the finger B be moved
to the point d (nine-tenths the distance between a and b), we shall have between d
and b, that is to say, at the terminals of the shunt b C B the same potential
difference as before. If then, means existed whereby the finger B would be moved
by reason of this change in current strength to the point d, the movement of the
finger B to said point would show that a current of 100 amperes was passing. And
thus the position assumed by finger B would indicate the current strength; and if
said finger B controlled a marking device making a trace on a regularly moving
record surface, a continuous record of the variations in strength of the current
would be produced.
Referring next to Fig. 2, here the body A may be an insulated wire wound in
spiral form and having a portion of the insulation removed on each turn along a
line extending from one end of the wire to the other as it is coiled. The finger B.
moves over and in contact with the non-insulated points. The point b of the
body A and the pivot point c of the finger B are connected in circuit. There will
then be a definite fall of potential over the body. A and depending on the resistance
thereof. This will be maximum when the finger B is placed at the point a, and
decrease as said finger is moved toward point b. Therefore any falling off of
pressure in the circuit can be compensated for by changing the position of finger B
so as to cut out more or less of the resistance of body A, and hence the extent of
movement of finger B will be in relation to change in pressure in the circuit. Hence
the position of finger B will indicate pressure variation provided means be supplied
to move said finger automatically whenever such change occurs. A scale being
arranged in proximity to finger B, the position of said finger may be noted thereon
and thus the extent of electrical pressure directly read.

page_text: Referring now to Figs. 3 and 4, 5 and 6, D is a dynamo. A represents the
resisting body, being a conducting bar of uniform cross-section in Fig. 3, or the
spiral wire above described in Fig. 4. At F is an instrument consisting of two
electro-magnets having their poles at G, H, Figs. 5 and 6. Between these poles is
a fixed cylinder of iron, I, which is surrounded by a pivoted coil, J, of fine wire.
A spiral spring, M, (or springs) is fastened to the pivot shaft, L, of this coil
and to a fixed abutment and operates to oppose or counterbalance the rotary
movement of the coil in the magnetic field which occurs when said coil is traversed
by a current.
At N is another instrument having permanent magnets, O, P, with pole
pieces, Q, R, common to both. A cylinder of iron is supported between these pole
pieces and in the annular field thus formed is a pivoted coil, T, the shaft, V, of
which has springs, S, which oppose and counterbalance its motion in manner similar
to the springs M of instrument F. On the pivot shaft is an arm, W, which vibrates
between adjustable stops, X and Y.
In instrument F, the coil J is composed of two oppositely-wound coils, J J.
The pivot shaft, L, of these coils carries the finger B which makes contact with
the body A, and which carries a pencil, C, which touches a sheet of paper, D!,
which by suitable mechanism is moved along at a definite speed. On the paper
is a scale-marking indicating hours and amperes, in Figs. 3 and 5, and hours and
volts in Figs. 4 and 6. The body A in Figs. 3 and 5 may also be marked to
indicate amperes.
The circuits in the arrangement shown in Figs. 3 and 5 are as follows: Circuit
No. 1 proceeds from the dynamo by conductor e to A, by e' to the lamps and thence
by to the dynamo. Circuit No. 2 proceeds by wire to field coils of
instrument F and thence by wire f¹ to the dynamo. Circuit No. 3 begins at the
point on A, proceeds by wire g to coil T of instrument N, to pivot shaft V, by
wire g¹ to shaft L, to finger B, to hody A, to main lamp circuit, to dynamo and
point of beginning b. Circuit No. 4 proceeds from dynamo, by wire h to middle
point between coils J J'; one branch then proceeds through coil J', wire h¹ and
stop Y in instrument N, and the other through the oppositely-wound coil J, wire h¹,
to adjustable stop X in instrument N.
The operation is as follows: Assume finger B to be at point a of body A and
the circuit-closing arm W to stand between the stops X and Y. The springs in
instrument F are made so weak that if the finger B be moved to any position over
arm A by hand it will remain indifferently in such position. Suppose the current
strength to increase. Then the increased current passing through wire g to coil T
will cause that coil to vibrate and take a new position bringing arm W into contact
with stop Y. Circuit is thus made through wire to coil J', to wire h, to dynamo.
Therefore coil J' rotates and the shaft L will be moved to carry finger B over A
toward point b. The effect of thus shortening the fractional part of A is to reduce
the potential difference in the circuit as explained in connection with Fig. 1, and
as the potential difference falls, coil T tends to return to its normal position.
Finally when the difference is reduced to that at which the instrument is originally
set, the arm W will leave its stop Y and return to its position out of contact with
either stop.
The finger B therefore feels a place on the body A between which and the end b
of said body there is the same fall in potential as originally existed in the circuit
before the current strength was increased. The trace of the pencil C on the
finger B across the moving scale D will show the current variation in amperes, and
the trace of the pencil vertically or in the direction of movement of the scale will
show the times when these variations in current strength occur. If the current
falls in strength, then on passing through wire g in circuit No. 3 it causes the arm W
of instrument N to move into contact with stop X whereby circuit is completed
through the coil J of instrument F and thence by wire back to the dynamo. In
such case the shaft L of instrument F moves in the opposite direction from that in
which it moved when the oppositely-wound coil J' was traversed by the current,

page_text: and therefore the finger B is carried back toward the end a of the body A until a
new place is found, when the arm W of instrument N once more leaves its stop.
Referring now to the arrangement of the instrument as a voltmeter, shown in
Figs. 4 and 6, circuit No. 1 proceeds from the dynamo by conductor e through the
body A to the finger B, to pivot shaft L, by wire gl to pivot shaft V, to coil T in
instrument N and thence by g to the dynamo. Circuit No. 2 proceeds by wire f to
the field coils of instrument F and by wire f' to the dynamo. Circuit. No. 3
proceeds from the dynamo by wire g through the coil T of instrument N to arm W,
and thence, when said arm is in contact with stop Y, through the wire and coil Ji
in instrument F and by wire to the dynamo; or, when the arm W is in contact
with stop X, through the wire " to the coil J and to the dynamo by wire h.
When no current is passing, the finger B is at the point a of body A and the lever
arm W is in contact with stop X. When the current is established it passes
through wire g to coil T, to wire, coil J and thence by wire h back to the
dynamo. The coil J will then tend to move so as to carry the arm W out of
contact with stop X and into contact with stop Y. The current will then be
diverted through wire and coil J, thus causing the finger B to move over the
body A until it reaches a point where the decrease of resistance compensates for
the change in potential and then the arm W will move away from stop Y. So long
as the pressure remains constant, the arm W will stand between the stops X and Y
making contact with neither, and the finger B will remain at rest, the pencil
point C producing a straight line on the record surface. The iustant, however,
that a variation in pressure occurs, the arm W moves into contact with one or the
other stop, X or Y, and the current is diverted into one or the other coil J or J',
and the finger B is moved in one or the other direction to modify the length of A
in circuit (and hence the resistance) to compensate for the change. In so moving,
as already explained the pencil point C makes its record on the continuously-
travelling scale.
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. A recording ammeter constructed and operating substantially as herein before
described.
2. A recording voltmeter constructed and operating substantially as hereinbefore
described.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.