Electric Resistance Meter and Rheostat.
Year: 1888

page_text: Date of Application, 10th Sept., 1888
Complete Specification Left, 11th June, 1889-Accepted, 3rd Aug., 1889
PROVISIONAL SPECIFICATION.
An Electric Resistance Meter and Rheostat.
I URBAIN EUGENE GUERIN of No. 95 Boulevard Beaumarchais Paris in the
Republic of France, Electrical Engineer, do hereby declare the nature of this invention
to be as follows:-
It is,
This invention relates to an instrument for measuring electric resistances.
like other such known instruments for this purpose based on the principle of the
Wheatstone Bridge, but it is so arranged as to be very sensitive, capable of being
readily and rapidly applied, and suitable for exact determination of the resistanco of
carth contacts, lightning or other conductors notwithstanding passage of earth currents
through the branches of the bridge. The instrument can also be used as a rheostat.
In order to illustrate the mode of obtaining great sensitiveness, I refer to the
diagram Fig. 5 illustrating a Wheatstone Bridge in which X is the resistance to be
measured, R the resistance box, G the galvanometer, P the battery and I the contact key.
In order that the galvanometer shall not be affected the ratio must be equal
to
B. C
C. D
*
A. B.
A. D.
If at the same time A. B+ A D = BC + CD, X must be equal to R and
AB to BC. The value of X may vary, R correspondly varying, whilst A.;B and
BC remain unchanged. If for instance, A. B and B. C were in one case each 1 ohm,
while X and Rare cach 10 ohms, and if in another case X and R were each 100 ohms,
the current in ABC would still find the same resistance 2 ohms, whilst that in
A. DC would find 20 ohms in the former, and 200 ohms in the latter case. As in derived
circuits the intensities are inversely as the resistances, the quantity passing A B C
would in the former case be 10 times that passing A DC, under which conditions
the galvanometer would work satisfactorily. But in the latter case, when the
quantity passing ABC is 100 times that passing A. DC, the action on the galvanometer
very feeble, and therefore variations of a few ohms more or less could scarcely be
detected. I have therefore found it necessary to vary the resistance of the
branches A B and BC, still however maintaining a constant ratio of AB to A D
and B (to CD as represented in Fig. 6, when 1 and r indicate resistances introduced
in A. B and B. C, these being always proportional to R however it may be varied so
201
that always
and r¹ + X = r + R when XR;-R being a case of resis-
X R
tances consisting of coils connected in series, and are each a similar case of the same
number of coils, each having the constant ratio, such as 1 to 10, to each of the coils of R.
The values of and have to vary simultaneously with that of R, and for effecting
this automatically, the instrument according to my invention is specially adapted, as
I will describe referring to the drawings which illustrate one example of such an
instrument adapted for a maximum resistance of 150 ohms. In the diagram Fig. 7, 8
resistance coils R of 1, 224, 10 20, 40, 80 ohms respectively are introduced in the
branch C. D. 16 others are arranged in two groups each of 8, rand having propor-
tional values such as 0.1, 0.2, 0.2, 0.4 also 1, 2, 4 and 8 ohms in the branches A B
and. BC. The coils of 1, 2, 2 and 4 ohms are coupled to those of 0.1, 0.2, 0.2 and 0.4
and those of 10, 20, 40, 80, with those of 1, 2, 4 and 8, the whole forming 8 groups
of 3 coils in proportion as indicated by the dotted lines in the plau Fig. 3. In Fig. 4
is shown a perspective of one of the groups consisting of 3 coils of Rr and having
their ends fixed to 3 parallel conductors corresponding with the branches D. C, B. C
and B. A of the bridge as indicated in Fig. 8. Their ends m are connected to contact
""

page_text: springs C, cand c¹ Fig. 4 respectively, and the other ends n to adjustable screws V, v, a
with which the springs may make contact. The spring C, c, c¹ are fixed to an
insulating block B and the screws V, v, are in insulated pieces as shewn more fully
in Fig. I which is a front view with the side of the casing removed and in Fig. 2,
which is an end view with the end of the casing removed.
The springs C&c. bear against ebonite rolls g-on levers L pivotted on pins A on
angle brackets E, and the levers are pressed by springs so that studs e projecting from
them bear against toothed discs D; the number and length of the teeth of each disc
varies according to the intended effect of the lever L which bears against it, in intro-
dacing or cutting out resistances. The discs are fixed on spindles K which can be
turned by a handle M, so that the discs moving the levers L make and break
contacts for the several sets of resistances. The casing of the instrument contains
in its upper part the counter mechanism under the base of which are fixed the
resistance coils. R. 7, and a galvanometer G is fitted to slide out or in, being
connected by a flexible conductor; there is also a clockwork I which can be started
by a push p. By the posts n no o¹ the instrument is connected to the resistance
to be measured and to a battery; by connecting to the posts u u, the instrument
can be used as a rheostat. The counter separates the resistance coils R into two
series, the one including the unit coils on the right these being of 1, 2, 2
and 4 ohms making up together 9, and the other on the left consisting of the
resistances 10, 20, 40 and 80 making up 150 ohms. Each series consists of
4 groups each of 3 coils R, r; thus in the unit series the 1st group has 1 ohm
and the coils R, 701 01 the second has 2 ohms and the coils R2, 10-2
and so on; in the 10 series, the 1st group has 10 ohms and the coils R10 7, "the
2nd has 20 and the coils R, 72, 72 and so on. To save space the levers L are
arranged on each side of the spindles K each of which carries a disc O graduated
in equal divisions which can be seen through a glass d in the cover.
0.2
A roller H pressing against a star wheel J of 10 teeth ensures the turning of the
spindle K through 1/10th of a revolution. When the studs e are in the hollows of
the discs D, the corresponding resistance coils are in circuit, when they ride over the
protuberances of the discs, their respective coils are cut out of circuit. Each of the
dises D is toothed differently to suit the group of coils which it controls, as will be
understood by the following example. When the disc O shows 0 or zero all the levers L
are on protuberances of their discs, no resistances being introduced into the circuit.
On turning the spindle 1/10th, 1 ohm is introduced by the drop of lever L; for
2 ohms L, is raised and L, is dropped, for 3 ohms both L and L, are dropped, and so
on until for 9 ohms all the levers L to L, are dropped. In a similar way, the series
of resistances advancing by tens are introduced, these being indicated on the disc 01
which has 16 divisions. The spindle K¹ for the tens is worked from the unit spindle K
by carrying gear such as is used in counters, each revolution of K causing movement
of K through one division. The spindle K¹ may however be turned independently
by applying the handle M to its end. Obviously the range of tho instrument may.be
extended to include a greater number or value of resistances, and by the addition of
known resistances in the circuit, the instrument may be used for great resistances.
Thus by adding a group of coils R, rr of 160, 16 and 16 ohms respectively, the in-
strument arranged itself for 150 ohms can be made to measure up to 310 ohms and so on.
In applying the instrument to measure resistance of earth contacts, lightning or
other conductors, I employ, instead of the usual contact key, the clockwork I which can
be started by the push p. There are two interrupters S, S₁ the one in the earth or
other circuit, the other in the battery circuit, worked by the two toothed cams N so as
io cause openings and closings of the two circuits so rapid as to prevent polorisation.
Besides these parts there is a reversing key so that observations may be made with
currents in both directions. When the instrument is used as a rheostat only the
branch B C (Fig. 7) of the bridge is employed, this being connected to the posts u u¹
Fig. 3.-

page_text: Obviously the instrument may be variously arranged to operate as above described
for measuring any numbers or fractions of ohms and may be applied in connection with
ampère meters, voltameters, rheostats and other instruments.
Dated this 10th day of January 18ee
ABEL & IMRAY,
Agents for the Applicant.
.to
CD.
If at the same time A B + AD = BC +, CD, X must be equal to R and A B to B C.
The value of X may vary, R correspondly varying, whilst AB and BC remain
unchanged. If, for instance, A B and BC were in one case each 1 ohm, while. X
and R are each 10 ohms, and if in another case X and R were each 100 olims, the
current in A B C would still find the same resistance 2 ohms, whilst that.in A DO
would find 20 ohms in the former, and 200 ohms in the latter case. As in derived
circuits the intensities are inversely as the resistances, the quantity passing A B C
would in the former case be 10 times that passing A DC, under which conditions the
galvanometer would work satisfactorily. But in the latter case, when the quantity
passing A B C is 100 times that passing A DC, the action on the galvanometer is very
feeble, and therefore variations of a few ohms more or less could scarcely be detected.
.I have therefore found it necessary to vary the resistance of the branches A B and BC,
still however maintaining a constant ratio of A B to AD and BC to CD as represented
in Fig. 6, where and r indicate resistances introduced in A B and B C, these being
201 r
always proportional to R however it may be varied, so that always
+X+R, when X = R.
✗ R
and
R being a case of resistances consisting of coils connected in series, and are
each a similar case of the same number of coils, each having the constant ratio, such
as 1 to 10, to each of the coils of R.
The values of r and have to vary simultaneously with that of R and for effecting
this automatically, the instrument according to my invention is specially adapted, as
I will describe referring to the drawings which illustrate one example of such an
instrument adapted for a maximum resistance of 150 ohms.
In the diagram Fig. 7, 8 resistance coils R of 1, 2, 2, 4, 10, 20, 40, 80 ohms
respectively are introduced in the branch CD. 16 others are arranged in two groups
each of 8, and having proportional values such as 0.1, 0.2, &c. (1.2, 0.4, also 1, 2, 4

page_text: and 8 ohms in the branches A B and B C. The coils of 1, 2, 2 and 4 ohms are coupled
to those of 0.1, 0.2 and 0.4, and those of 10, 20, 40, 80 with those of 1, 2, 4 and 8, the
whole forming 8 groups of 3 coils in proportion as indicated by the dotted lines in
the plan Fig. 3. In Fig. 4 is shewn a perspective of one of the groups consisting of
3 coils of R, and having their ends fixed to 3 parallel conductors corresponding
with the branchés DC, BC and BA of the bridge as indicated in Fig. 8. Their
ends m are connected to contact springs Cc and c¹ (Fig. 4) respectively, and the other
ends n to adjustable screws V with which the springs may make contact. The
springs Cc care fixed to an insulating block B and the screws Vvvare in insulated
pieces as shewn more fully in Fig. 1 which is a front view with the side of the
casing removed, and in Fig. 2 which is an end view with the end of the casing
removed.
с
The spring Ccc bear against ebonite rolls y on levers L pivotted on pins A on
angle brackets E, and the levers are pressed by springs so that studs e projecting from
them bear against toothed discs D; the number and length of the teeth of each dise vary
according to the intended effect of the lever L which bears against it, in introducing or
cutting out resistances. The discs are fixed on spindles K which can be turned by a
handle M so that the discs nioving the levers L make and break contacts for the several
sets of resistances.
The casing of the instrument contains in its upper part the counter mechanism
under the base of which are fixed the resistance coils R, and a galvanometer G is
fitted to slide out or in, being connected by a flexible conductor; there is also a
clockwork I which can be started by a push p. By the posts n no o¹ the instrument
is connected to the resistance to be measured and to a battery; by connecting to the
posts u u¹, the instrument can be used as a rheostat.
-
The counter separates the resistance coils R into two series, the one including the
unit coils on the right these being of 1, 2, 2 and 4 ohms making up together 9, and the
other on the left consisting of the resistances 10, 20, 40 and 80 making up together
150 ohms. Each series consists of 4 groups each of 3 coils Rr; thus in the unit
series the 1st group has 1 ohm and the coils R, -1, the 2nd has 2 ohms and
the coils R, 0.21 110
0.2 and so on; in the 10 series, the 1st group has 10 ohms and
the coils R011, the 2nd has 20 ohms and the coils R20 722 and so on.
0.1
To save space, the levers Laro arranged on each side of the spindles K, each of which
carries a disc O graduated in equal divisions which can be seen through a glass d in
the cover.
A roller H pressing against a star wheel J of ten teeth ensures the turning
of the spindle K through 1/10th of a revolution. When the studs e are in the
hollows of the discs D, the corresponding resistance coils are in circuit, when they
ride over the protuberances of the discs their respective coils are cut out of circuit.
Each of the discs D is toothed differently to suit the group of coils which it controls,
as will be understood by the following example:
When the disc O shows 0 or zero all the levers Lare on protuberances of their
discs, no resistance being introduced into the circuit. On turning the spindle 1/10th,
1 ohm is introduced by the drop of lever L₁, for 2 ohms L₁ is raised and L, is dropped,
for 3 ohms both L₁ and L₂ are dropped and so on until for 9 ohms all the levers I
to Lare dropped.
In a similar way the series of resistances advancing by tens are introduced, these
being indicated on the disc O¹ which has 16 divisions.
The spindle K¹ for the tens is worked from the unit spindle K by carrying gear such
as is used in counters, each revolution of K causing movement of K¹ through one
division. The spindle K₁ may however be turned independently by applying the
handle M to its end.
Obviously the range of the instrument may be extended.to include.a,greater number
or value of resistances, and by the addition of known resistances in the circuit the
instrument may be used for great resistances.
Thus by adding a group of coils R, 1 of 160, 16 and 16 ohms-respectively the
instrument arranged itself for. 150 ohms can be made.to measure up to 310 ohms, and
so on.

page_text: In applying the instrument to measure resistance of earth contacts, lightning or
other conductors, I employ, instead of the usual contact key, the clockwork I which
can be started by the push p. There are two interrupters S S' the one in the earth or
other circuit, the other in the battery circuit, worked by the two toothed cams N so as
to cause openings and closings of the two circuits so rapid as to prevent polarisation.
Besides these parts there is a reversing key so that observations may be made with
currents in both directions. When the instrument is used as a rheostat only the
branch B C (Fig. 7) of the bridge is employed, this being connected to the posts u u¹
Fig. 3.
Obviously the instrument may be variously arranged to operate as above described
for measuring any numbors or fractions of ohms, and may be applied in connection
with ampère meters, voltameters, rheostats and other instruments.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what I
claim is --
1. An electric resistance meter wherein the resistances in the three branches of the
bridge are varied simultaneously, maintaining their constant proportion, substantially
as described.
2. In a resistance meter of the kind referred to, avoiding the influence of oarth
currents by rapidly opening and closing repeatedly the circuits of the battery and of
the resistances, substantially as described.
ABEL & IMRAY,
Agents for the Applicant.