Year: 1886

page_text: Date of Application, 23rd Feb., 1886.
Complete Left, 16th Nov., 1886.
Complete Accepted, 11th Jan., 1887.
[Communicated from abroad by JOHN W. HOWELL, of the City of New Brunswick,
in the County of Middlesex and State of New Jersey, United States of
America, Electrical Engineer.]
I BENJAMIN JOSEPH BARNARD MILLS of the firm of Harris & Mills of 23
Southampton Buildings in the County of Middlesex, Patent Agent do hereby declare
the nature of this invention to be as follows:-
This invention relates to an instrument for indicating changes in the electro-motive
force or for measuring the same and is intended especially for use in systems of
electric lighting to indicate variations of electro-motive force, so that the generators
may be regulated accordingly.
The invention is an improvement on an indicator which has heretofore been
extensively used for this purpose and which consists of a Wheatstone Bridge
consisting of a parallelogram of wires connected between the points of the circuit
at which the electro-motive force is to be measured or indicated. In two opposite
sides of the parallelogram are connected incandescing electric lamps having carbon
conductors.
In the other two sides are placed wire resistances. One of these is adjustable and
has a scale for indicating the degree of adjustment.
A galvanometer is connected across in a bridge as usual. Changes in electro-
motive force in the circuit cause changes in the temperature and therefore in the
resistance of the carbon conductors of the lamps, but do not vary the wire resistance
to any practically appreciable extent. This causes current to pass through the
galvanometer whose needle is deflected thereby. The adjustable resistance is then
regulated until the needle resumes its original position, and the amount of such
adjustment which has been necessary shows what the change of electro-motive force
has been.
The object of the present invention is to produce an instrument operating sub-

page_text: stantially on the same principle as that just described, but cheaper and more compact
in construction and more accurate, convenient and efficient in operation than that
instrument. In one of the two arms of a Wheatstone Bridge are placed an incan-
descing electric lamp and a wire resistance. In the other arm are placed three wire
resistances.
The galvanometer is in the bridge between the two sides, and one of its terminals
is connected with a contact which travels upon the middle one of the three wire
resistances in one side, which wire resistance is composed of insulated coils wound
closely together but having the insulation removed along one side so that a bared
surface is formed along which the aforesaid contact can move whereby the galvano-
meter terminal is connected at different points in said coils.
In the operation of the instrument this connection is first so adjusted that the
galvanometer needle stands at zero with the standard electro-motive force or that
which is desired to maintain in the system. An increase in this electro-motive force
increases the temperature and decreases the resistance of the carbon conductor of a
lamp. This destroys the balance of resistance, and current therefore flows through
the galvanometer. The deflection of the galvanometer shows the amount of increase
in electro-motive force.
A decrease in electro-motive force causing an increase in the resistance of the
lamp causes current to pass through the galvanometer in the opposite direction so
that this also is indicated.
As has been stated, in the instrument hitherto employed, two lamps are employed
in opposite sides of the bridge.
In this case, if the lamps are of equal resistance, the sum of the two wire
resistances has to be equal to or greater than the sum of the two lamp resistances.
Further, the wire of each of the wire resistances has to be of sufficient conductivity
to carry the current of the lamp in series with it.
For these reasons a great length of large wire which is expensive and occupies a
great deal of space has to be used.
Now with the present arrangement this is not so, for; let A equal the wire
resistance in the lamp side of the bridge, B the lamp resistance, C the lower of the
two main resistances on the other side, and D the other one of these two. Then the
proportions are A: B:: C: D, and by making D of fine wire and high resistance
which can be done because it does not have to carry the lamp current, the resistance A
can be made of very low resistance and therefore it is necessary to use only a
short length of the heavy wire necessary to carry the lamp current. The two
resistances C and D also are mado of fine wire and therefore this instrument
effects a large saving in expense of wire and in bulk over the old instrument.
The inventor prefers to make the resistance of D about 1000 ohms. The resistance
of A is such that the lamp is not brought to its full candle power and its permanency
is thereby assured.
In the practical construction of the instrument there is employed a suitable
enclosing box or case of wood or other suitable material provided with a base board
for attachment to a wall or other object.
The resistance coils are wound on frames, spools or rods which are supported by
screws passing into them through the sides of the box.
Parallel to the rod which carries the middle or adjusted resistance coils is a rod
which has on it a moveable sleeve which has a handle for moving it, said handle
passing through a slot in the front of the box and having upon it a pointer which
travels along a scale above the slot. A set screw is provided which sets against the
rod to hold the sleeve at the point at which it is placed.
On its inner side the sleeve carries a contact spring which travels upon the bared
portion of the resistance coils as has been described.
The adjustable galvanometer terminal is connected with a screw which passos
through the side of the case and whose point makes or breaks contact with a plate
attached to the rod in which the sliding contact moves whereby the galvanometer
current is made or broken,

page_text: The galvanometer is supported within the case. Its pointer extends out in front
of a scale placed behind an opening in front of the case.
The lamp is placed in a socket on top of the box. It is inclined, so that the lamp
will throw its light on the indexes and scales at the front of the box.
Instead of a galvanometer, there may be used an instrument, which records as well
as indicates the changes. For this purpose it is preferred to have a metal cylinder
revolved by clock-work or other mechanism over which runs a strip of cheinically
prepared paper, such as is used with chemical telegraph instruments.
Upon the surface of the paper rest two metal pens one of which is connected with
the moving resistance contact and the other between the resistances in the opposite
arm of the bridge in the same manner as the galvanometer is connected in the form
previously described.
It is evident that so long as there is no difference of potential between these
terminals there will be no marks made upon the paper, but when current flows across
the bridge in one direction or the other, one pen or the other, according to direction
of current will leave a mark upon the moving paper.
A permanent record of changes in electro-motive force is thus provided.
B. J. B. MILLS.
By Harris & Mills,
23, Southampton Buildings,
Agents.

page_text: BENJAMIN JOSEPH BARNARD MILLS of the firm of Harris and Mills of
23 Southampton Buildings in the County of Middlesex, Patent Agent do hereby
declare the nature of this invention, a communication to me from abroad by JOHN
W. HOWELL of the City of New Brunswick in the County of Middlesex and State of
New Jersey, United States of America, Electrical Engineer, and in what manner the
same is to be performed, to be particularly described and ascertained in and by
the following statement :--
Reference being had to the drawings hereunto annexed, and to the figures and
letters marked thereon, that is to say,
This invention relates to an instrument for indicating changes in electro-motive
force or for measuring the same and is intended especially for use in systems of
electric lighting to indicate variations of electro-motive force, so that the generators
may be regulated accordingly.
The invention is an improvement on an indicator which has heretofore been
extensively used for this purpose and which consists of a Wheatstone Bridge
consisting of a parallelogram of wires connected between the points of the circuit at
which the clectro-motive force is to be measured or indicated.
In two opposite sides of the parallelogram are connected incandescing electric
lamps having carbon conductors. In the other two sides are placed iron resistances.
One of these is adjustable and has a scale for indicating the degree of adjustment.
A galvanometer is connected across in a bridge as usual.
Changes in electro-motive force in the circuit cause changes in the temperature and
therefore in the resistance of the carbon conductors of the lamps, but do not vary
the wire resistance to any practical appreciable extent.
This causes current to pass through the galvanometer whose needle is deflected
thereby.
The adjustable resistance is then regulated until the needle resumes its original
position and the amount of such adjustment which has been necessary shows what
the change of electro-motive force has been.
The object of the present invention is to produce an instrument operating substan-
tially on the same principle as that just described, but cheaper and more compact in
construction and more accurate, convenient and efficient in operation than that
instrument.
The invention is illustrated in the annexed drawings in which Figure 1 is a
theoretical diagram illustrating the principle of the invention: Figure 2 is a diagram
which shows also some features of construction: Figure 3 is a perspective view of
the instrument with part of the case broken away. Figure 4 is a view of a portion
of the adjustable resistance which is employed; and Figure 5 is a diagram of a
modification of the invention.
Referring first to Figure 1-1, 2, are the points of an electric circuit, the electro-
motive force or difference of potential between which is to be indicate 1.
The parts of the instrument form a Wheatstone Bridge connected between said
points 1. 2.

page_text: In one side of said bridge are a resistance A, and an incandescing electric lamp B.
In the other side are a resistance C, a resistance D, and between these two a
resistance E.
The galvanometer F, is in the bridge between the two sides. One of its terminals
is connected with the contact a which travels upon the coils of the resistance E whose
construction will be presently explained.
The operation of the instrument may be generally explained with relation to
Figure 1. The connection of the galvanometer to the resistance E, is first adjusted
so that the galvanometer needle stands at zero with the standard electro-motive force
or that which it is desired to maintain in the system.
An increase in the electro-motive force increases the temperature of the carbon
conductor of the lamp B, and hence decreases the resistance thereof. This destroys
the balance of the resistances and current flows through the galvanometer in the
direction of the arrow in Figure 1. The deflection of the galvanometer shows the
amount of the increase in electro-motive force. A decrease in electro-motive
force causing an increase in the resistance of the lamp, causes current to pass through
the galvanometer in the opposite direction so that this also is indicated.
In the old form of indicator above described two incandescing electric lamps are
employed as sensitive resistances, one in each arm of the Wheatstone Bridge, and
wire resistances, one of which is adjustable, are also placed one in each arm.
In this arrangement if the lamps are of equal resistance, the sum of the two iron
resistances has to be equal to or greater than the sum of the two lamp resistances.
Further the wire of each of the wire resistances has to be of sufficient conductivity
to carry the current of the lamp in series with it. For these reasons a great length
of large wire which is expensive, and occupies a great deal of space, has to be used.
In the present arrangement however as the proportions are A: B:: C: D by
making the resistance D, of fine wire and high resistance, which can be done because
it does not have to carry the lamp current, A can be made of very low resistance
and therefore it becomes necessary to use only a short length of the heavy wire
necessary to carry the lamp current. The resistances C and E also are made of
fine wire and therefore this instrument effects a large saving in expense of wire and
in bulk over the old form.
It is preferred to make the resistance D, of about 1000 ohms. Resistance A, is
such that the lamp B is not brought to its full candle power and its permanency is
thereby assured.
It will be seen of course, that so much of the resistance E, as may be on the right
of the adjusting contact forms in reality part of resistance D; while those coils
which are on the left form part of resistance C.
The
Figure 2 better illustrates the practical arrangement of the circuits. H, H',
represent the binding posts which are the terminals of the instrument.
resistance coils are wound upon suitable spools or. frames. In this Figure the
resistance adjusting contact which is the terminal of conductor 3, is not shown.
The instrument itself is shown in Figures 3 and 4.-I, is a suitable inclosing box
or case of wood or other suitable material, with a base board I' which may be
attached to a wall or other object.
K is a suitable frame upon which the two sets of resistance coils C and D are
wound.
This frame is supported from the side of the box by screws c. A similar frame L
supported in the same way by screws d carries the resistance coils B. Coils E are
wound upon a bar M also carried from the sides of the box by screws, not shown. A
rod N extends parallel to M, and on this is a moveable sleeve e which has a handle f
for moving it, said handle passing through a slot g in the front of the box and
having upon it a pointer h which travels along scale i above the slot. A set screw f
is provided which sets against rod N to hold the contact at the point at which it is
placed.
On its inner side, sleeve e carries the contact spring a. The coils E are of
insulated wire bent on one side, the insulation is filed or scraped off and the spring a

page_text: travers along this bared portion so that its movement connects the galvanometer to
different parts of the coil E.
At one end (see Figure 4) the end plate extends out against the front of the case
and a screw m passes through the case so as to make contact with or break it if the
screw is turned.
To this screw the wire 3 from the galvanometer is connected, and thus the
galvanometer shunt may be made and broken as desired.
The galvanometer F, is supported from the back or base board of the case.
Its pointer o extends out in front of a scale O placed behind an opening P in the
front of the case. The scale is supported by arms pp extending from the galvano-
meter. Qis the device for neutralizing the effect on the galvanometer of the earth's
magnetism, the bar being turned by screws and held in any position by spring t.
On the top of the box is the lamp socket R for holding lamp B. It is inclined
as shown so that the lamp will throw its light on the indexes and scales at the front of
the box. Also by placing the lamp outside the box the size of the box may be much
diminished.
The circuit connections are not shown in Figure 3: the wires pass through the
wood of the box.
The connections will be readily understood from the preceding explanations.
In operating the apparatus sleeve e is moved until the galvanometer needle stands
at zero.
When any changes occur in electro-motive force in the circuit such changes are
seen upon the galvanometer scale and the generators supplying current to the circuit
are regulated in accordance with these indications. The variations may also be
indicated by scale i. When the galvanometer is deflected, resistance E is regulated
so as to bring it back to zero, and the amount of such regulation indicated upon
scale shows what the amount of change of electro-motive force has been.
This is the preferred way when the instrument is used as a temporary indicator
to measure various different electro-motive forces. When the instrument is used as
a permanent indicator, as in the station of an electric lighting system, to indicate
variations in one electro-motive force the galvanometer scale is usually read. Figure 5
illustrates a form of apparatus by which a permanent record of electro-motive force
is obtained.
The arrangement of circuits and resistances is the same as already described. S, is
a cylinder preferably of metal revolved by suitable clock work or other mechanism
over which runs a strip T, of chemically prepared paper such as is used with chemical
telegraph instruments.
Upon the surface of the paper rest two metal pens s and s¹ which are suitably
supported and one of which is connected with the moving resistance contact, and
the other between the resistances in the opposite arm of the bridge in the same
manner as the galvanometer is connected in the form previously described.
It is evident that so long as there is no difference of potential between these
terminals there will be no marks made upon the paper, but when current flows across
the bridge in one direction or the other, one pen or the other according to the
direction of current, will leave a mark upon the moving paper. This indicates the
variations in electro-motive force and at the same time leaves a permanent record
which shows when the electro-motive force has been high or low and when it has
remained constant. This form of instrument is well adapted for use on vessels where
the motion may affect the ordinary indicator.
An additional advantage of using one lamp in the indicator instead of two, is that
an incandescing electric lamp is liable to develop defects in use which make uncertain
the indications dependent upon it. It is evident that with two lamps the liability to
error in this way is just twice as great as when only one is used.
Having now particularly described and ascertained the nature of the said invention,
and in what manner the same is to be performed, I declare that what I claim is :-
1. In an electrical indicator the combination of a resistance, sensitive to changes

page_text: in temperature, as an incandescing electric lamp and a wire resistance in one side of
a Wheatstone Bridge and two wire resistances in the other side, all such resistances
being proportioned substantially as described, and an indicator or recorder of current
connected between the two sides, substantially as hereinbefore described.
2. In an electrical indicator wherein resistances are placed in opposite sides of a
Wheatstone Bridge and a current indicating device is connected between said sides so
as to be affected by changes in such resistances, connecting a terminal of the
indicating device adjustably with a resistance in one side of the bridge, substantially
as hereinbefore described.
3. In an electrical indicator the combination of an incandescing electric lamp and
a wire resistance in one side of a Wheatstone Bridge, three wire resistances in the
other side, and a current indicator or recorder connected between the two sides, one
of whose terminals is connected with a contact adjustable upon the middle one of
the three resistances, substantially as hereinbefore described.
B. J. B. MILLS.
By Harris & Mills,
23, Southampton Buildings,
Agents.