surements.
Year: 1898

page_text: [Communicated from abroad by Professor EDWARD ROSA, of Wesleyan University,
Middletown, State of Connecticut, United States of America.]
Curve Tracer of Electrical Measurements.
I, WILLIAM CLIVER SMITII, of 101, St. Martin's Lane, in the County of London,
Electrical Engineer and Manufacturer, 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:
My invention relates to the measurement and plotting of the instantaneous
values of periodic electric quantities such as currents electromotive forces and
power and its object is to provide an apparatus which will enable these quantities
to be accurately and rapidly measured and also to be plotted simultaneously and
automatically to a predetermined scale. Such record is neat and permanent
and shows not only the magnitude and manner of variation of each of such electric
quantities but also shows their phases relatively to one another.
This instrument utilizes the so-called "instantaneous contact method" of
measurement. A disc of some non-conducting material is mounted upon a shaft,
and the latter is connected with the armature of a dynamo or a synchronous motor,
so that in either case it revolves with the same speed as the generator which
supplies the current to be measured. The brush" which makes contact (once
in each revolution), with a metallic knife edge let into the revolving disc, has
heretofore usually been advanced step by step by hand. One of the features of
this invention consists of advancing the brush automatically by means of suitable
gears, driven by a ratchet wheel, which in turn is actuated by a lever and pawl
or an electromagnet and pawl, or some other suitable device.
One of the other features of this invention is the measuring solenoid, by means of
which measurements of the electric quantities are quickly and accurately made by
a null method, a sliding or rolling contact being adjusted until there is no
current in one of the circuits, as shown by no deflection in a galvanometer, or by
silence in a telephone by any other suitable means.
Another part of the apparatus is the recording cylinder, joined to the measuring
solenoid by a pantograph, the latter carrying a pen or pencil or other means of
making points. The excursions of the sliding contact, which measure the
instantaneous values of the electric quantities, are repeated on a reduced scale
by the marking point, of the pantagraph, and so transferred to the recording
cylinder, in a manner to be hereafter described. This being done automatically,
the time and labour of measuring and plotting electric curves is by this invention
reduced to a small fraction of what it has heretofore been, and the accuracy and
taithfulness of the curves is much enhanced.
To more fully describe my invention, reference is had to the accompanying
drawings, in which :-
-
Fig. 1 represents my improved apparatus and its electrical connections in
diagram, illustrating the operations of the same.

page_text: number of turns of wire wound uniformly in one layer, the insulation being
removed along the top for making electrical contact with the contact maker E,
which is free to move over the solenoid from a to y.
N represents an electric circuit passing through either of the resistances R
or R', through the instantaneous contact maker B, through the galvanometer G,
contact E and through that portion of the solenoid F between the sliding con-
tact E and a fixed contact O' in the centre of the solenoid; and M is a key for
closing and opening this circuit.
It will, therefore, be seen that when the contact piece bon the disc of the
instantaneous contact maker comes in contact with the brush 3, an instantaneous
current will be sent through the circuit N when the contact M is closed, and
will, if the sliding contact E is at represent the strength of the current of the
dynamo A at that particular phase of the cycle corresponding to the position of
the brush 3. But if at the instant of the closing of the circuit by the contact
maker B, the difference of potential between E and O is the same as that
between, there will be no deflection of the galvanometer. If there is a
deflection of the galvanometer, E may be moved one way or the other until there
is none.
Then the distance may be taken as the measure of the difference of
potential of R and hence of the current in the primary circuit. Obviously, if
the flow of the current is from to r, the sliding contact E will be placed on the
left of O, and if from to r, E will be placed on the right of O. If, then, the
brush of the instantaneous contact maker is moved through a small angle,
contact is made at a different phase of the current and consequently there will be
a new position of E for a balance; the new value of E O being a measure of the
current at the instant of contact. In this way by advancing the brush 63 step by
step, and setting the sliding contact E each time, so as to have no deflection of
the galvanometer, a series of readings may be made from which the curve of
current may be constructed, point by point. Then connecting the resistance R¹
instead of R in the circuit N, a new act of readings may be taken for the secondary
current. In order to avoid the labour of recording numerous readings from the
different settings of the contact E, and subsequently plotting them by hand, I am
enabled by my improved apparatus to plot these values automatically as the set-
tings are made. For this purpose the pantagraph D is attached to the sliding
contact E and carries on the cross bar the electro-magnetic recording point or
pencil K, so that as shown in the drawing, the distance K is one-fifth of E°, or
obviously, this proportion may be varied at will. Then as E is moved along the
solenoid F the space passed over by K will be one-fifth of that passed over by E.
Now assuming that at the position of E, as shown in the drawing, there is no
deflection of the galvanometer G, when the contact M is closed and the instantaneous
contact is made through the brush 63, then for that position of the brush 63 and
hence that phase of the current of the dynamo, the electro-magnetic recorder K
may be made to print a point on the surface C by closing the contact M¹, and in
addition to actuating the recorder K the current through M excites the electro-
magnets Bo which immediately attract their armatures and set the pawls 65,
but upon breaking the contact at M¹, the magnets Bº being no longer excited
and the springs 18 withdrawing the armatures, cause the pawls 65 to advance
the brush and surface C a pre-determined distance and hence set them in a
position for a new reading to be recorded. The contact E is then moved to a
new position, (the contact M being closed) until the galvanometer ceases to deflect,
when the process of recording above described is repeated, and so on for a
sufficient number of readings to obtain a curve on the surface C, of the electrical
quantity thus being determined. This curve is made up of a line of dots which
represent the successive positions of the contact E and is shown in Fig. 6.
The specific structure of the instantaneous contact maker is shown in Figs. 2, 3,
and 4. B2 represents any suitable base upon which is mounted the pedestals B3
and B, and journalled in these pedestals is the shaft B5, which as before explained,
may be either directly coupled to the armature shaft of the dynamo A, or may be

page_text: with the pinion c². This pinion is rotated step by step at such times as the
magnet 10 is excited, by the mechanism in every respect the same as that which
advances the brush 3 of the instantaneous contact maker, all of which was
described in detail with reference to Figs. 2, 3 and 4. The cylinder C is adapted
to carry a sheet of paper; preferably co-ordinate paper Co, upon which the records
of the values is printed.
The solenoid F' consists as before described of a great number of coils of insulated
wire wound on a core f, which core is mounted in the upright F. The insulation
is removed from the top of the wire of the solenoid so that a contact maker passing
over the said solenoid may make electrical contact therewith. The contact maker,
most clearly shown in the detailed view Fig. 8, consists of a contact screw E which
passes through a block e², the latter being grooved on one side to receive the
solenoid. The same result may be accomplished by having the solenoid wound
with bare wire with the convolutions separated from each other, and the block e²
made of insulating material. This contact maker E is shifted along the solenoid
by means of the cord H, which passes over the pulleys F2. The spring / between
one end of the cord and the contact maker takes up the slack in the cord and by
turning either of the milled heads F3, the contact maker is shifteil either to the
right or left. The sliding contact E is secured to one end of the pantagraph D
the other end of which is mounted on the rod e¹. The end of the pantagraph, so
mounted on the rod e', is adapted to slide thereon and to be clamped in any desired
position by the set screw c. The cross bar of the pantagraph carries the
recorder K. This recorder consists of a pointed instrument which may be
either a pencil or a sharpened piece of metal, which is secured to an iron core k',
and this core ¹ is adapted to fit loosely in the solenoid k, being held in its normal
position by the spring, so that when a current passes through the coil of the
solenoid, the core will be drawn down and cause the point to strike the paper
under it and thus make a dot thereen which will represent the value of the
electrical quantity at that instant being measured.
The recording may be accomplished by using 3 as a pencil; or, a ribbon
similar to typewriter ribbons, may be placed between the paper and the recording
point and the record taken in that way; or a sheet of carbon paper may be sub-
stituted for the ribbon, and indeed there are many ways of making the record
visible which are all more or less obvious.
If the dynamo is a four-pole machine the two ratchets 64 64 are advanced the
same number of teeth each time, and one full wave of current extends half way
around the cylinder. If the dynamo is a two-pole machine, the ratchet on the
contact maker is advanced four teeth, while that on the cylinder advances two.
1t the dynamo has eight poles, then the ratchet on the contact maker advances
one tooth, and that on the cylinder two. For a sixteen-pole machine, I advance
one tooth on the contact maker to four on the cylinder, &c.; but in any case the
current curves would be drawn to the same scale.
It will readily be seen from the foregoing description that the position of
the recording cylinder is entirely independent of the instantaneous contact maker,
as one may be placed in proximity to the dynamo, and the other may be situated
in any convenient place. But on the other hand they may both be mounted on
the same shaft or otherwise mechanically coupled together, and the pawl that
advances the ratchet may be actuated by a lever.
By suitably choosing the resistance R and R', the current curves may be
drawn to any desired scale; and by using a large non-inductive resistance in
parallel with the circuit of either resistance, the current in the parallel circuit will
be in phase with the corresponding electro-motive force, and hence the curve
drawn therefor will be the electromotive force curve.
I am thus enabled by the hereindescribed apparatus to plot the curves of many
other electrical quantities as watts or power, magnetization, hysteresis and eddy
current curves, and indeed the apparatus is adapted to a great variety of uses, and
gives permanent records of great beauty and accuracy.

page_text: current, a periodically moving recording surface moving in synchronism with the
said brush and means for recording on the said recording surface the values
obtained from the various positions of said brush, substantially as described.
9. In apparatus for recording instantaneous values of electrical quantities, the
combination with an electric circuit carrying an alternating current, of an
instantaneous contact maker provided with a brush adapted to move periodically
and to complete said electric circuit at successive intervals in a cycle of the
alternating current, a recording surface adapted to move periodically and in
synchronism with said brush a pantagraph mounted near said recording surface,
a recorder carried by said pantagraph, a sliding contact maker carried by said
pantagraph and a solenoid adapted to engage said sliding contact maker, sub-
stantially as described.
10. In an instantaneous contact maker, the combination with a rotatable disc, of
a contact strip mounted in the periphery of said disc, a brush adapted to engage
the periphery of said disc, means for conveying the current to and from said
contact strip and brush when the said strip and brush engage each other, and
means for automatically imparting angular step by step motion to the said brush,
substantially as described.
11. In an instantaneous contact maker, the combination with a shaft, of a disc
mounted on said shaft and adapted to revolve therewith, a conducting strip
mounted in the periphery of said disc, a brush adapted to make contact with said
conducting strip once in every revolution of the said disc, an arm carrying said
brush, mounted on said shaft and adapted to advance the said brush step by step
around the said disc, and means for conveying the current to and from said brush
and contact piece, substantially as described.
12. In an instantaneous contact maker, the combination with a shaft, of a disc
mounted on said shaft and adapted to rotate therewith, a conducting strip mounted
on the periphery of said shaft, a brush adapted to make contact with said con-
ducting strip periodically, an arm carrying the said brush and mounted on said
shaft, means of conveying the current to and away from the said brush and
contact strip, and an electromagnet for giving angular step by step movement to
the said arm, substantially as described.
13. In an instantaneous contact maker, the combination with a shaft, of a disc
of insulating material mounted thereon and adapted to rotate therewith, a
metallic contact blade mounted in the periphery of said disc, a brush adapted to
engage the periphery of said disc and to make contact with said contact blade
periodically, an arm carrying said brush, means for conducting the current to
and away from said brush and contact blade, means for imparting angular step
by step movement to said brush and arm, and an electro-magnet for actuating the
said means, substantially as described.
14. In an instantaneous contact maker, the combination with a shaft, of a disc
mounted on said shaft and adapted to rotate therewith, a contact blade mounted
in the periphery of said disc, a brush adapted to engage the periphery of said
disc and to make contact periodically with said contact blade means for conducting
the current to and away from said brush and contact blade, an arm mounted
loosely on said shaft and carrying said brush, a gear mounted on said arm, a
ratchet and pawl for rotating said gear, an electro-magnet and spring for actuating
said pawl, so that the said brush is advanced step by step around the periphery
of said disc, substantially as described.
15. In an instantaneous contact maker, the combination with a shaft, of a disc
mounted on said shaft and rotating therewith, a contact blade carried by said
disc, a brush adapted to engage the periphery of said disc and to make contact
periodically with said contact blade, means for conveying the current to and away
from the said brush and contact blade, an arm carrying said brush and mounted
loosely on said shaft, a gear wheel attached to said arm, a pinion meshing with
said gear, a shaft carrying said pinion, a ratchet and pawl adapted to rotate said
shaft and pinion, an arm carrying said pawl, a depending arm secured to said. first

page_text: consists in instantaneously completing an electric circuit at successive intervals
in a complete cycle of the alternations of the current, maintaining the potential
in the said circuit at zero for each time that the instantaneous contact is made and
automatically recording the values of the current on a periodically and synchro-
nously moving surface, substantially as described.
Doted this 21st day of Jan 1808