IMPROVEMENTS IN DEVICES FOR MEASURING THE ELECTRIC CURRENT PASSING THROUGH OR USED UPON CERTAIN CIRCUIT
Year: 1881

page_text: A
LETTERS PATENT to Edward Griffith' Brewer, of 33, Chancery Lane, in the
County of Middlesex, for an Invention of "IMPROVEMENTS IN DEVICES FOR
MEASURING THE ELECTRIC CURRENT PASSING THROUGH OR USED UPON
CERTAIN CIRCUIT." A communication from abroad by Thomas Alva Edison,
of Menlo Park, in the State of New Jersey, United States of America.
PROVISIONAL SPECIFICATION left by the said. Edward Griffith Brewer
at the Office of the Commissioners of Patents on the 25th April 1881.
EDWARD GRIFFITH BREWER, of 33, Chancery Lane, in the County of Middlesex.
"IMPROVEMENTS IN DEVICES FOR MEASURING THE ELECTRIC CURRENT PASSING
THROUGH OR USED UPON A CERTAIN CIRCUIT." A communication from abroad
by Thomas Alva Edison, of Menlo Park, in the State of New Jersey, United
States of America.
By means of the so called "Edison" current measuring apparatus the quantity
of current passing through a given circuit can be ascertained, as is well known.
Such arrangements as will accomplish this are especially desirable in a system
for furnishing electricity for light and motor purposes from one central station to a
large number of consumers in order that each consumer may be charged only
according to the amount actually used or consumed by him.
This present Invention relates to the same object, and is intended to furnish a
reliable means of measuring the current and to provide against some sources of
error not hitherto noticed.
For this purpose there is used as the basis of the meter a simple electro
deposition cell placed in a shunt to the main circuit so arranged that only a
definite fraction of the entire current shall pass therethrough, which may be
effected by placing a suitable resistance in the main conductor at a point between
the unions of the conductors of the shunt circuit thereto.
At stated intervals the cathode plate is taken from the cell and weighed, the
increase in result indicating the amount of current which has passed therethrough,

page_text: which, multiplied by the denominator of the fraction representing the portion
of current shunted, gives the amount consumed in the entire circuit to be
measured.
Upon the passage of the current through the cell the fluid therein is heated, it
may be to a very small extent, still there is a heating effect therein. This
diminishes the resistance of the cell and consequently a proportionately increased
amount of current passes therethrough, making an appreciable source of error.
To remedy this a resistance should be used in the cell circuit equally susceptible
to the heating influences of the current, but which increases in resistance as it is
heated. By this means, as the resistance of the cell is diminished the artificial
resistance in its circuit is increased, so that the entire resistance of the shunt or
electro-depositing circuit is maintained constant. A resistance of fine copper wire
answers well for this purpose.
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In constructing the meter for actual use it is preferable to use two cells, one
arranged so that its rate of deposition is a multiple of the other, the meter box
being divided into two portions, one of which, viz., the one containing the cell
wherein deposition is the more rapid, being arranged to be opened by the inspector
on his rounds, the other being locked and used as a "check meter."
This difference of deposition may be accomplished readily by using circular
anode or cathode plates, the containing vessel constituting the other pole, the
circular plates varying in diameter in the-two-cells-used.
Each cell has a circuit from the main circuit, but a common return circuit to
the main circuit may be used for both containing the compensating resistance before
spoken of.
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page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Edward Griffith Brewer in the Great Seal Patent Office on the
25th October 1881.
EDWARD GRIFFITH BREWER, of 34, Chancery Lane, in the County of Middlesex.
"IMPROVEMENTS IN DEVICES FOR MEASURING THE ELECTRIC CURRENT PASSING
THROUGH OR USED UPON A CERTAIN CIRCUIT.". A communication from abroad
by Thomas Alva Edison, of Menlo Park, in the State of New Jersey, United
States of America.
This Invention relates to apparatus for measuring the quantity of electric
current passing through a circuit in a given time, and is one of those devices to
which the name "Vebermeter was given in British Letters Patent, No 4391, of
Oct. 27 1880.
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It has for its object the ensuring of greater accuracy in recording when in various
conditions as to temperature.
This arrangement generally consists of an electro-depositing cell, the anode and
cathode of which are plates the weight of which has been carefully determined.
It is placed in a shunt circuit to that of which the current has to be measured, the
latter containing a resistance, so that a definite proportional part of the current
will be shunted through the cell. After the lapse of a proper interval of time the
cathode and anode plates are weighed and the difference in weight noted,' this
difference showing the amount of current which has passed through the shunt
(or only one may be weighed), and this being proportional to the current on the
inain circuit the latter is easily determined.
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In practical use, however, a rise or fall of temperature would decrease or increase
the resistance of the cell and so allow a larger or a less quantity of current to pass
through the shunt circuit.
To obviate this phenomenon a metallic resistance, preferably of copper, is placed
in the shunt, which increases when the temperature rises, while the resistance of
the cell diminishes..
This resistance, therefore, must be proportioned to that of the cell; for instance,
if the latter contains a 20 per cent. solution of copper sulphate the copper wire
resistance must be three times as great as that of the cell in order that they may
continue to balance and render migatory the effects of a rise
temperature.
and fall of
In practice it may be well to use two cells in one of which the deposition takes
place with greater rapidity than in the other, the former being opened, inspected,
and weighed at proper intervals, while the latter is kept locked, and used as a
"check meter" to ensure absolute correctness in the charges, and to protect the
seller. of electricity from fraud.
Suitable devices for carrying this Invention into effect are shown in the Drawings
in which
Figure 1 is a front elevation of a box or case containing two cells, which
constitute a meter.
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Figure 2 is an elevation of the two cells with diagram of the circuit connections
and resistances.
Figure 3 is a detailed view in section of a portion of a cell, and
Figure 4 is a section of another form of cell which may be used.
A is a box containing the two electro-depositing cells B, C, one of which, B, is
arranged to deposit with greater rapidity than the other, this being easily
accomplished by varying either the size of the plates, their distance apart, the
strength of the solution, or the amount of current shunted through it.
The box has two doors, one of which, D, encloses only the cell C, which is
intended to be kept locked while the outer door E. is opened for inspection of the
cell B.
In Figure 2, 1, 2, are the main conductors, from which a derived or multiple arc
circuit 3, 4, leads into a house in which the meter B, C, is placed for measuring
the current passing through the house.

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Resistances R, R¹, deflect portions of the current into the shunt circuits 5, 6,
and 7, 8. the resistance R₁ being less than R so that a greater current' enters the
cell B than that which passes through C. "
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a, a, are the anode, and c, c, the cathode plates, one of which in each cell is
arranged so as to be withdrawn from the cell, while the other is permanently fixed
therein!
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8, 81, are resistances of fine copper wire placed in the shunt circuits.
In Figure 3 the arrangement for readily removing one of the electrode plates is
shown.
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A projection e with a rounded top extends above the top F of the cell, and the
plate is made with a curved. or hooked portion G which hangs over e and is
secured by a thumb-screw H, which also serves to secure the wire 7. The electrode
passes through an aperture f in the cover of the cell. The other electrode may be
held firmly, connection being made, thereto from the wire 8. by means of a set
screw J. The operation of these devices is as follows:-
1. Current passing through the shunt circuit 7, 8, deposits copper on the cathode c
of the cell B. If the solution in B becomes heated by the temperature of the
room rising its resistance diminishes, but at the same time the resistance is
increased correspondingly, so that the amount of current passing remains the same.
When measurements, are desired the door E is opened to obtain, access to the
cell B, the thumb-screw H is loosened and the plate c raised from the cell and its
increase of weight determined. From this the current passing through the main
line is computed.
If it is desired to substantiate or prove the indications of the cell B the cell C is
examined and one or both of its electrodes weighed, this cell being arranged to
allow of a smaller amount of, deposition than the cell B.
A convenient arrangement for accomplishing this is illustrated in Figure 4.
Here the cylinders a, ., form the anode and c,.c, the cathode, the difference in
diameter of a and c producing the difference in deposition. The cells are so
arranged in branch circuits, as seen in the Figure, that only one shunting
resistance rand' one compensating resistance t need be used,
What is claimed is,--
✓ First. A vebermeter, consisting of two electro-depositing cells, one of which
deposits with greater rapidity than the other, substantially as and for the purpose
described.
Second.The combination with an electro-depositing cell of a resistance, whose
increase compensates for the decrease in resistance of the cell, substantially, as set
forth.
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Third. The combination with the cathode plate of an electro-depositing cell
having a curved or hooked extremity of a projection extending above the
and a set-screw for attaching the cathode, plate to, the projection, substantially as
set forth.
Fourth: The combination in a,vebermeter of two electro depositing cells having
circular cathode plates of different diameters, substantially as and for the purposes
described.
Fifth. The combination in a vebermeter of two electro-depositing cells, one of
which acts as a check to prove the other, substantially as set forth.
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In witness whereof, I, the said Edward Griffith Brewer, bave hereunto
set my hand and seal; this Twenty fourth day of October, in the year
of our Lord One thousand eight hundred and eighty one.
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E. G. BREWER. (L.S.)."
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✓ Redhill Printed for His Majesty's Stationery Office, by Love' & Malcomson, Ltd. i