Year: 1887

page_text: Date of Application, 13th July, 1887
Complete Left, 12th Apr., 1888
Complete Accepted, 1st June, 1888
We, WALTER THOMAS GOOLDEN of 2 Victoria Mansions Westminster in the county
of Middlesex, electrical engineer, and SYDNEY EVERSHED of Kenley in the county of
Surrey, electrician, do hereby declare the nature of this invention to be as follows:-
In voltmeters in which the current in a coil is made a measure of the pressure on a
circuit, the variation in the resistance of the coil, due to varying temperature, causes
errors in the readings of such instruments; pressure regulators are affected by the
same errors.
In the well known Potentiometer which is used to obtain multiples of the
electro-motive-force of a standard cell, errors are caused by both the resistances of the
wires or coils in the instrument, and the electro-motive-force of the standard cell,
varying with the temperature.
The object of our invention is to make the readings or working of voltmeters,
pressure regulators and potentiometers independent of temperature, and we effect this
by winding the coils of such instruments with two or more wires having different
resistance temperature-coefficients (herein called the coefficients).
Thus according to our invention we wind the coil of a voltmeter or a pressure-
regulating device, partly with a wire having a small coefficient and partly with a
compensating wire having a large coefficient; the latter wire being coupled in shunt
to a portion of the former wire in such a way as to cause the current to flow in
opposite directions in the two wires. The resultant magnetic field of the combination
coil will then be equal to the difference of the fields due to the two wires, and, by
observing certain proportions between the resistances and number of turns of the two
wires and the resistance of the shunted portion of the wire having the small coefficient,

page_text: this difference may be made constant for constant pressure on the terminals of the
coil, throughout a large range of temperature.
In a potentiometer the pressure on the terminals when the current in the standard-
cell circuit is zero, is equal to the product of the electro motive-force of the cell,
and the ratio of the resistances of the two coils or wires used; and we make one or
both coils or wires partly of wire having a small coefficient and partly of wire having
a large coefficient, joined in series or in parallel to the first wire, of such resistances
as to give the ratio as a whole a virtual coefficient equal, but of opposite sign, to that
of the standard cell, so that the indications of the potentiometer are not affected by
temperature.

page_text: COMPLETE SPECIFICATION.
Compensating Electric Measuring Instruments for Temperature.
WALTER THOMAS GOOLDEN, of 2 Victoria Mansions, Westminster in the county of
Middlesex, electrical engineer, and SYDNEY EVERSHED, of Kenley in the county of
Surrey, electrician 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 :-
In voltmeters in which the current in a coil is made a measure of the pressure on a
circuit, the variation in the resistance of the coil due to varying temperature causes
In the
errors in the readings; pressure-regulators are effected by the same cause.
well known potentiometer which is used to obtain multiples of the electromotive force
of a standard cell, errors are caused by both the resistance of the wires or coils in
the instrument, and the electromotive force of the standard cell, varying with the
temperature.
The object of our invention is to make the readings or working of voltmeters,
pressure regulators etc., and of potentiometers, independent of temperature; and we
effect this by winding the coils of such instruments with two or more wires having
different temperature-resistance coefficients, herein call the coefficients.
That part of our invention which relates to voltmeters, pressure regulators, etc., is
applicable to (1) voltmeters as indicated in the first paragraph of this specification,
(2) regulators of electrical pressure, (3) regulators the action of which depends on
electrical pressure, and (4) the pressure circuits or coils of wattmeters, ohmmeters, etc;
and in this specification the term "pressure-apparatus" is used to signify any or all of
these apparatus.
In patent No. 3942, 1885 (Swinburne and Evershed) three methods of com-
persating voltmeters are described, namely: (1) arranging a resistance, having a
small coefficient, in series with a voltmeter, and a resistance, having a large coefficient,
in shunt to it; (2) arranging a resistance of large coefficient in shunt to one coil of a
dynamometer, and (3) winding a wire of large coefficient backwards round the coil of
a voltmeter and connecting it to the terminals of the instrument.
According to the present invention we wind the coil of a pressure-apparatus with
two wires having different coefficients and couple the wire of larger coefficient in
shunt to a portion only of the wire of smaller coefficient, in such a manner as to cause
the current to flow in opposite directions in the two wires, as indicated diagram-
matically in Fig. I of the drawings attached, where A and B are two portions of the
wire of small coefficient, herein called the working circuit, and C is the wire of large
coefficient, herein called the compensating circuit. The two circuits are wound so that
an average ampère-turn on C has an equal magnetic effect so far as the working of
the pressure-apparatus is concerned, to that of an average ampère-turn on A and B.
The whole current between the terminals of the pressure-apparatus, divides into two
portions, namely that in A, herein called the working current, and the remainder
in (, herein called the compensating current. The magnetic effect of the whole coil A, B,

page_text: and C, is proportional to the difference between the ampère-turns on the working
circuit and the ampère-turns on the compensating circuit; and by observing certain
proportions between the resistances, coefficients, and number of turns on A, B, and C
this difference, and consequently the magnetic effect of the whole coil is made
constant for constant pressure on the terminals throughout a wide range of tem-
perature. The proper proportions are either calculated or determined by experiment.
The method we prefer to adopt in practice, is as follows:-We make the number
of turns on equal to those on B; it is then obvious that the compensating current
has no magnetic effect on the pressure-apparatus since it makes an equal number of
turns forwards and backwards. If by virtue of position a turn on C has a greater or
less effect than a turn on B, the number of turns on C is diminished or increased
until the magnetic effect of the compensating current is zero. This adjustment being
made, the only magnetic effect of the whole coil is that due to the working current
and in order that the pressure-apparatus shall be independent of temperature the sole
condition is that the working current must be constant with constant pressure on the
terminals at varying temperatures. We calculate the proportions of the resistances
of A, B, and C by means of the following formula :—
in which denotes the resistance of that portion of the working circuit shunted by
the compensating circuit; C denotes the resistance of the compensating circuit;
R denotes the resistance of the whole of the working circuit; b denotes the coefficient
of the compensating circuit; and a denotes the coefficient of the working circuit.
A, and B together with C, may be used as separate working coils of the pressure-
apparatus, or the whole coil A, B, and C, may be used as one coil.
A may form one coil of a dynamometer, and B together with C the other coil; for
since the ampère-turns on each are constant, their product, on which the reading of a
dynamometer depends, is constant.
In order to compensate for the heating of the coils due to the power spent in the
pressure apparatus, we wind A, B, and C so that the heating shall affect them equally;
for the formula given is true so long as A, B, and C are at the same temperature;
thus we either wind the working and compensating circuits side by side, or in
alternate layers, or divide the bobbin into several sections and distribute the two
circuits equally among the sections.
The working coil of a pressure-apparatus is often wound with wire of high
conductivity, and a resistance formed of wire having a small coefficient is arranged in
series with it. The compensation of such apparatus according to our invention is
illustrated in Fig. II, in which W represents the working coil, S the series
resistance, and C the compensating circuit. In practice the working coil is usually
wound with copper, and we prefer to wind the compensating circuit with copper also,
and use platinoid, or platinum silver, for the series resistance. After winding the
coils we determine the resistance of that portion of S which must be shunted by C, by
calculation, or by experiment.
In a potentiometer the pressure on the terminals when the current in the cell
circuit is zero, is equal to the product of the electromotive force of the standard cell
and the ratio of the resistances of the two coils or wires used; and in applying our
invention to a potentiometer we form one or both coils or wires partly of a metal
having a small coefficient and partly of a metal having a large coefficient coupled in
series or in parallel to the first coil or wire, of such resistances as to give the ratio
coils as a whole a virtual coefficient numerically equal but of opposite sign to that of
the standard cell so that the indications of the potentiometer are not affected by
temperature.
Fig. III, illustrates the method we prefer to adopt in compensating a potentiometer
for temperature. B is the potentiometer resistance wire, on a portion of which,

page_text: denoted by A, the standard cell E and galvanometer G are arranged as a derived
circuit in the usual manner, and in order to render the arrangement independent of
temperature we form a part of B of a compensating wire having a large coefficient,
the remainder of B having a small coefficient; the compensating wire is placed in the
portion A or in the remaining portion of B according as the coefficient of the
standard cell is positive or negative. In Fig. III we have assumed the coefficient of
the cell to be negative as is generally the case, and C represents the compensating
wire the resistance of which we determine by the following formula :-
in which denotes the resistance of the compensating wire; R denotes the resistance
of the whole of B, including a; c denotes the coefficient of the standard cell ;
b denotes the coefficient of the compensating wire; and a denotes the coefficient of
the remainder of B.
When, as is sometimes the case, the resistance B is divided into a number of
sections to enable different multiples of the electromotive force of the cell to be
obtained by using one or more sections; we carry out our invention by introducing
into each section of B a portion of compensating wire of sufficient resistance to make
the above formula true for any number of sections which may be used.
true
It will be understood from the foregoing description of our invention that we
assume the variation, of resistance in the case of metal wires and of electromotive
force in the case of a standard cell, due to varying temperature to be constant
throughout a wide range of temperature. Although this assumption is not strictly
leads to sufficiently accurate results for the purposes of our invention since the
temperature errors to be corrected by compensation are never very large. If however
a coefficient is not sensibly constant we base our calculations on its average value
throughout the range of temperature for which the pressure-apparatus or the
potentiometer is to be compensated.
In the drawings attached to this specification; coils wires or circuits having a small
coefficient and those having a large coefficient are indicated by fine lines and by thick
lines respectively.
.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
1. Compensating the temperature errors in pressure-apparatus by means of a
compensating coil, wire, or circuit, arranged in shunt to a portion of the working coil,
wire, or circuit; substantially as described.
2. Neutralizing the magnetic effect of the compensating current, substantially as
and for the purposes set forth.
3. The employment of the shunted portion of the working circuit as one coil of a
dynamometer, and the remainder of the working circuit together with the com-
pensating circuit as the other coil.
4. Compensating the temperature errors in potentiometers by means of wires
having different coefficients; substantially as described.
1121 1
L
11000
WALTER T. GOOLDEN.
SYDNEY EVERSHED.