Method of and Apparatus for Directly Indicating the Value of Electrical Resistances
Year: 1895

page_text: Date of Application, 3rd May, 1895
Complete Specification Left, 21st Jan 1896-Accepted, 22nd Feb
1896
[Communicated from abroad by Messrs SIEMENS & HALSKE, of Berlin, in the
Geiman Empire, Llectical Engineers]
Method of and Apparatus for Directly Indicating the Value of
Electrical Resistances
We, SI MENS BROTHERS & CO LIMITED, of 12, Queen Annes Gate,
Westminster, in the County of Middlesex, Electrical Fngineers, do hereby
aeclare the nature of this invention to be as follows
No apparatus has been constructed up to the present time whereby the value of
a resistance required to be measured can be read off from an indicator, if any
electromotive forces whatever are simultaneously combined with the resistance,
and wherein no battery (introduced for the purpose of the measurement), has
exercised an influence over the indication
The present invention has for its object to enable such an apparatus to be
constructed, ard is based upon the following observation
If a certain electromotive force acts in each branch of the curient-diagram of a
Wheatstones bridge F 1 of the accompanying drawing and the resistances differ
to any optional amount, (no introduction of external ie istances having been
effected,) and if the curient be varied in the one diagonal branch D the relation
of the current-variation in the other fixed diagonal bianch d to that in the first
named vable one is independent of all the electromotive forces, and is only
dependent upon the resistances of the four side branches and of the fixed diagonal
branch
If for example the resistance of the diagonal branch D be varied so that at
first a current J exists therein, and afterwards the current J', while in the diagonal
branch d the collesponding curients and ¹ exist, then, if w₁ w² w³ 20 are the
resistances of the side bianches, and w the re istance of the fixed digon il branch d,
the said clation will be
be observed, and if the resistances w w¹ u² w³ wo are 1nown, with the exception of
one, for instance, u', then w¹ can be determined by the aid of the above equation
independently of the electromotive forces, from the ascertained value of

page_text: motive forces except those in the branch D, and if this branch containing the
battery be simply opened and closed, then
If now for example w¹ be the unknown resistance, and if the resistances ww²
wow be known and constant, the scale of the instrument can be so ginduated that
the value of 20 can be directly read off therefiom This deflection is then
independent of all the electromotive forces
For producing the current differences - ¹or J-J₁ and supplying them to the
galvanometer there ne employed, generally speal ing, two induction apparatus, as
indicated at Fig 3, the pumary windings P, p of which are combined respectively
in the bianches D d and whose secondai y windings Ss are combined respectively
with the directing coils and with the deflecting coils a a, to form circuits
There then exist in the two secondary circuits of the induction apparatus,
currents which are proportional to the differences of the currents in the primary
circuits
If no great accuracy is required, the induction apparatus in D can be omitted
and the directing coils can be duectly connected with D
If
If electromotive forces exist in the side bianches as well as in the diagonal
branch D, then an terupter is introduced into D by means of which this bianch
an either be opened and closed on a resistance can be put in or out of circuit
this interuption is only effected once, then the ballistic deflection in the instrument
will be proportional to
If this interruption be repeated in regular sequence, then a constant deflection
will be obtained which is a measure of that proportion
Assuming the before mentioned subsidiary forces to be neglected, it will then be
immaterial at what speed the interrupter works, starting from a certain limit
If a galvanometer be used as indicator, then cue must be taken that the current 4

page_text: impulses have one and the same direction in the galvanometer, by providing a
second current interrupter working synchronously with the first one
If no electromotive forces are present beyond those in D the interrupter and the
induction apparatus are dispensed with the current is then led ducctly through
the deflecting coils, and the current through the directing coils
If there exist alternating currents in the side branches, then, for the indication
of the resistance of one of these side branches the same method is employed as
for the cast when no electromotive forces act, that is to say, there are introduced
into the one diagonal branch battery and the directing coils of the galvanometer,
and into the other branch the deflecting coils of the galvanometer
The application of this method extends over the entire field of measurement of
electrical resistances
In electrical installations it is especially a question of the continuous indicition,
during the working, of the total insulation, the insulation of the separate
conductors in the so called two-three &c wire systems, and the localisation of
a fault, and this is required both for continuous and for alternating curient
installations
For the indication of the total in ulation of a continuous current installation we
employ preferably the arrangement shewn at Fig 4
}
Any point of the installation (in Fig 4 a three-wie system with insulatio
faults fff³ is assumed) is connected with the indicating apparatus, the
insulation resistance of the installation forms the branch 1 of the bridge diagram
point W is connected with earth
The variable diagonal branch D contains firstly the contact C which is opened
and closed at regular intervals, and by means of which the resistance U, which
may even be infinitely great, is put in and out of circuit, secondly the battery B,
which in certain cases is omitted, and thirdly the primary coil P of an induction
apparatus, whose secondary coil S acts on the directing coils r r of the galvanometer
The fixed diagonal branch d contains the primary coil p of a second induction
apparatus whose secondary coil is combined in one and the same circuit with the
periodically operating contact c and the deflecting coils a a of the galvanometei
The contact is so aanged that only the induced currents produced in s at the
opening or at the closing of the cont ict C are passed into the deflecting coils
The scale of the galvanometer is so divided that the insulation resistance of the
installation can be directly read off
For indicating the faults in the separate conductors of a continuous current
installation we employ preferably the arrangement shewn at Fig 5
The two diagonal branches remain the same as in the insulation indicator, the
end W of branch D is put to earth, X is connected to one conductor, Y with the
contiguous conductor
The deflection of the galvanometer shews a certain relation of resistance which
is not simply definable if the several pairs of conductors I II, II III, III I
are consecutively introduced, and the respective deflections at read off then from
these and from the value of the total insulation the faults of the sepaint
conductors can be calculated or read off from prepared tables
For indicating the locality of a fault in a continuous current installation, w
employ in particular the arrangement at Fig 6
The two diagonal branches remain as before W is put to earth X and Y ar
connected for example by feeders with the points V V₁ of a distributing conductor
through which a curient flows, between which points is situated the fault F
The galvanometer branch is connected with the said points for example by pilot
wires
The deflection of the galvanometer shews the proportion of the resistances V F
V₁ F, the scale is so divided that the deflection will indicate directly the position
of the fault between the points V V¹
If a fault occurs in the installation, this is at once indicated by the apparatus is
connected up for the insulation test By switching over, the connections are then

page_text: changed for indicating the particular conductor on which the fault exists, and by
a farther switching over for localizing the fault
In order to indicate with alternating curient installations the total insulation,
the conductor faults, and the locality of the faults, the same connections as for
continuous urient installations are made out the diagonal branches are altered,
the induction apparatus and the periodical contacts c c are dispensed with, the
branch D only has a permanently connected bittery B and the directing coils r?,
the branch d has the deflecting coils a ant Fig 7
If there are no electromotive forces tive in the silo bianches then, as shewn
at Fig 8, the diagonal branches D d are arranged as foi alternating current
installations the deflection of the galvanometer then gives directly the resistance
of the able side branch, for example of 1
This latter arrangement may serve for transferring the indications of any
instrument to a distant locality
For example the pointer H Fig 9 of the instrument is made to slide with a
contact piece along a wire or over contact plates between which resistances w are
introduced, and the wires are led from those parts to a bridge apparatus with
battery and galvanometer situated at the distant point, the deflection of the latter
will then give directly the amount of the resistance introduced at 1, or the position
of the pointer, independently of the strength of the battery B
Dated this 3rd day of May 1895
ABEL & IMRAY,
Agents for the Applicants
wak Apparatus for Directly indicating
Electrical Resistances
ьце value от
We, SILMFAS BROTHERS & CO LIMITED of 12 Queen Anne's Gate, Westminster
in the County of Middlesex, Electrical Engineers, 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
This invention relates to methods for measuring electrical resistances containing
electromotive forces
Methods are known by which an electrical resistance can be measured whether it
is by itself a seat of an electromotive force or not But the execution of all known
methods of this hind includes the adjustment of a number of known resistances
according to a fixed rule
Other methods for measuring electrical resistances not including electiomotive
forces are known, in which the adjustment of known resistances is superfluous, and
in which the measurement consists in simply reading the deflection of a simple
instrument However, with these method, the exactness of measurement depends
upon the constancy of the battery or other source of electromotive force
employed
This invention relates to a method and apparatus for measuring electrical
resistance by the simple reading of an instrument and without any adjustment of
rheosats, the exactness of the measurement being independent of variations of the
electromctive force employed, and the method being likewise applicable whether
the resistance to be measured is itself a source of electromotive force, or not
Referring to the diawings accompanying the Provisional Specification let there
be a system of resistances as in Figure 1 like in the Wheatstone bridge, consisting
of 4 branches, 1, 2, 3, 4 and 2 diagonals d, D,—these resistances not being adjusted
according to any fixed rule, as in the Wheatstone bridge, but having any values,
and elcctiomotive forces of any amount acting in all the branches
If, in this

page_text: system, the current flowing in the diagonal D is varied at will by varving the
resistance or the electromotive force of this branch, the currents in all other
branches being consequently varied, the quotient of the variation of the current
in D divided by the variation of the current in d is independent of all the electio
motive forces in the system and depends only on the values of the resistances of
the different branches, the varying diagonal branch excepted
2
If I designates the current in D and the current in d, and if the equation of
the systems are laid down according to the rules of Kuchhoff so as to deduce th
expressions of the currents J, flowing in the diagonal, it is seen that each of
these currents depends on all the resistances and on all the electromotive forces in
the system
If the current J be now varied to J¹ by changing the resistance or the electro-
motive force or both in the diagonal D, the current 1, in the aiagonal d, will also
change its value to ', and the expressions for the currents J, , will readily be
found by putting the new values of the resistance and the electromotive force in the
branch Dinto the expressions of J¹ and ¹ 1 he expressions of J¹ and ¹ depend
also on all the resistances and electiomotive forces
But if the differences J-J¹ and be taken and the latter be divided by
the former, this quotient will depend neither on any electromotive force, noi on the
resistance of the diagonal D but only on the resistances of the side branches and of
the diagonal d
The expression for this quotient is the following
the resistances in the side branches 1, 2, 3, 4 being designated by w', w³, w³, w' and
the resistance of the diagonal d, which is not vaned, by w Neither the electro-
motive forces, nor the resistance of the varving diagonal D appears in the
expression
Consequently if the value of the ratio
is observed in any way, and if one of the resistances, for instance w¹, is unknown,
its value can be determined To the known resistances other values may be given
to obtain greater sensibility, but their values must always be known
If no electromotive forces e pre.ent except that in the varying diagonal D,
and if the variation of this diagonal is got simply by opening and closing it
This equation is a special case of equation (1) and holds good, though the
current J may not be varied at all and the diagonal D is not opened
2
2-21
This equation is a special case of equation (1) and holds good, though the
current J may not be varied at all and the diagonal D is not opened
2
For indicating the ratio of 1-11 there may be employed a galvanometer or
electro-dynamometer provided with two fixed coils arranged in such a way that the

page_text: field created by excitation of the one cuts at right angles the field created by the
excitation of the other
Thus one pan of coils diagrammatically represented by rrin Figure 2 is used
to give the needle ns (if a galvanometer is used) a fixed direction, whereas the
other pair diagrammatically represented by a a is used to cause a deflection of
the needle I or this purpose the coils are made such that their directing
influence on the needle is practically infinitely great as compared with the magnetic
field of the earth or other directing influences that may come into play
Consequently if the directing coils are excited by a current, the strength of
which is proportional to J. 11 and the deflecting coils a a by a current the strength
-', the deflection will merely depend upon the value
of which is proportional to
of the quotient
-
If, for the magnetic needle, ns of the galvanometer, be substituted swinging
coil traversed by a curent, it is connected in series or in parallel with one of the
fixed coils or sets of coils If the two currents travcising the fixed coils are 2- - z¹
and JJ respectively, and the swinging coil is connected with the first of the two,
the force exerted by the first coil will be proportional to the value of the
expression (21) and the force exerted by the other will be proportional
(J― J¹) + (22) Consequently the deflection caused by the united action of
both fixed coils oi sets of fixed coils will depend on the value of
corresponding to the deflection of the galv nometer needle, as stated above
Now assuming w' to be the unknown resistance and further assuming 20, 202, 203, 204
to be known and invariable, it is evident that the instrument can be graduated so as
to allow the value of w¹ to be read directly
In order to excite the coils
connected
for me,
and a a according to the above rules, they may be
as shewn in Figure 3, with the secondary coils S and s of two trans-
the primary coils Pand p of which are inserted in the diagonals D and d
of the bridge As is well known, the current induced in a secondary coil in a
given time is proportional to the difference between the current flowing in the
primary coil at the beginning and the current flowing in the primary coil at the end
of the time
Consequently, if the current J in the diagonal D is by any means changed to the
value Jand in the same time the current in the diagonal d to the value 2',
the electric impulse induced during this time in the coil S will be proportional to
the difference JJ' and the impulse induced during this time in the coils will be
proportional to the difference, and if the coils rraie connected to S, the
coils a a to s, and an instrument is constructed by combining the coils r r, a a and
needle or a swinging coil, as above set forth in reference to Figure 2, the move
ment of the needle or of the swinging coil caused by the change of current in D will
be proportional to the quotient
If rough measurements are considered sufficient, the transformer in the branch D
can be dispensed with and the galvanometer colls inserted directly into the 4
diagonal D
In case other electromotive forces are present in the lateral branches of the
bridge besides the one acting in the diagonal D, a make and break switch is inscited

page_text: in the diagonal D, as diagrammatically represented by C m Figure 4, by which
the diagonal D can be opened and closed oi a te istance U Figure 4 can be included
or excluded
If this interruption takes place only once, a bullistic deflection of the galvanometer
will follow which will be proportional to the value of the quotient
If however the make and break is operated continuously a constant deflection of
the galvanometer is obtained which constitutes a measure of the value of the said
quotient In that case, if the frequency of the periodical interruptions is increased
above a certain limit the rate of this frequency becomes practically negligible
If a galvanometer is used, the deflection of the needle will alter its direction and
value according as the current impulses flowing through the two sets of coils a a
and
rie synchronous o ne subject to a gieater or less difference of phase
In this case suitable means should be adopted to ensure the syncliionism of the
impulses in both sets of coils
If alternating currents are flowing through one or more of the lateral
branches 1, 2, 3, 4, of the bridge, the connections employed for measuring the
16sistance of one of these lateral bianches are the ame as if no electromotive forces
are present, that is to say, the directing coils rr and a battery B are inserted
directly in the one diagonal D, the deflecting coils a a in the other
If this method be employed for insulation measurements during the regular working
of electric light and power installations, three problems will have to be treated in
the first place, namely, the measurement of the total insulation resistance of the
installation, or of the resultant leakage, the measurement of the insulation
resistance of every single branch of a two-wire system and the finding of the
position of a fault or leak In all these cases the method is substantially the same,
though the connections employed in every case have to be slightly varied in order
to be adapted to the special requirements
The treatment of special cases, given as examples, illustrates the practical
applicability of the general method forming the subject of this invention
For measuring the total insulation resistance of continous curient installation
without interrupting its regular working, the connections diagrammatically
represented in Figure 4 may be employed
The installation is assumed to be constructed upon the plan generally known as
a three wire system I, II, III, with the dynamo machines, this example being
chosen because this system is most frequently employed in such installations
From what follows it will be readily understood that the same method and
connections are also applicable to a two we or a multiple wire system
I he total insulation resistance which may be termed the "resultant leak" this
expression meaning the resistance of all leaks present in the installation at the time
of measuring arranged in parallel between the mass of conductors constituting the
installation and earth, is represented by the zigzag lines f¹ƒ ƒ³, converging into
an arrow head which is to be understood as representing an earth-connection in
this and the following diagrams
Point W of the bidge is connected with earth, point X of the bridge is
connected with any suitable point of the working installation
In this case the resultant leak of the installation constitutes the latter branch 1
of the budge The diagonal D contains a make and-break switch C which is arranged
in any known way suitable for causing periodical interruptions by alternately
including and excluding the resistance U, which may have any suitable value or
may be made infinitely great There is also inserted in the diagonal D the
battery B and the primary coil P of a transformer, the secondary coil S of which
is connected with the duecting coils rr of the galvanometer represented in
Figure 2 The other diagonal a contains the primary coil p of a transformer, the

page_text: secondary coils of which is connected with the deflecting coils a a of the galvano-
meter In the secondary circuit of this transformer a second make and break
switch c is inserted, which is arranged is such a way as to operate in synchronism
with the switch C so that only currents of the same direction pass through the
coils a a and rr If the galvanometer has been suitably graduated, the total
insulation resistance can be read directly, expressed in any desired units
In order to find the value of the resultant leak of any one of the branches of a
similar installation the connections diagrammatically represented in igure o are
preferably employ ed The diagonals D and d remain the same as in the
preceding case, with the difference that the end of the diagonal D is connected to
earth as indicated by W Point X is connected with one branch of the installation,
point Y with another The deflection of the galvanometer, is then measure of
the value of a certain relation of resistances which is not easily defined by a few
words
However, if one after another different pairs of branches of the installation
are connected according to the rule given, that is to say, bist the branches, I and II
then the branches II and III and finally the branches III and I and the correspond-
ing deflections of the galvanometer are observed, it is possible from these dates, and,
from the value of the total insulation resistance to calculate the desired values of
the leak of every single branch, or these latter can be found by reference to a
table calculated beforehand
In order to find the position of a leak in continuous current in tallation
the connections diagrammatically represented in Figure 6 a preferably
employed
The diagonals D and d again remain the same as in the preceding case, the
W end of branch D again being put to earth
The points X and Y are connected to two points V and V between which the
leak oi fult F is supposed to be situated, in the mains or feeders of the
installation For carrying the diagonal d up to such a point the test wires
belonging to the same conductors may be used but special wires may be employed
for these connections
The deflection of the galvanometer will be a measure of the value of the ratio
between the resistance VF and V H 2 it can be graduated in such way that the
position of the needle corresponds with the position of the leak between the
points V and V1
If the bridge connection is mounted in such a way as to remain constantly
connected with the installation it will be readily understood, that it can be easily
arranged in such a manner that it will instantly indicate a leakage of the insulation
and then by operating a switch, fist the leakage of every branch of the insulation
can be read and then the position of the leak determined
Io determining the value of the resultant total leakage, of the leak ige of one
branch and the position of a leak in alternating current installations the same
connections are employed as those described for continuous current install itions,
with the role exception that the arrangement of the diagonals of the bridge may
be simplibed
The
The transformers and the make and break switches can be dispensed with
diagonal I need only contain a battery B, and the directing coils rr of the
galvanometer, in the diagonal d only the deflecting coils a a are inserted as shewn
in Figure 7
In case no electromotive forces whatever are present in the lateral branches this
san e arrangement can be employed The deflection of the galvanometer will then
be a direct measure of the variable resistance of a lateral branch, for instance of
the branch 1 I his case is illustrated by Figure 8
Figure 9 illustrates an airangement by which the method can be employed for
the purpose of indicating at a distance the exact position of a clock hand or similar
apparatus The hand H is so arranged as to connect the point W of the bridge with
various points of the rheostat w, the resistance of which is by this means and by
the conductors inserted between the points W and X of the bridge

page_text: Thus the deflection of the galvanometer becomes direct mea-ure of the
resistance, inserted between Zand X and if suitably graduated, will thereby
ndicate the exact position of the hand independently of the strength of the
battery B
Having now particularly described and ascertained the nature of the said inven-
ion and in what manner the same is to be performed we declare that what we
laim is
-
1 A method for measuring an electrical resistance combined with unknown
clectromotive forces acting therein, consisting in placing the resistance to be
measured in one of the lateral branches of Wheatstone-bridge and by varying
by any suitable known means the strength of the current flowing through one of the
diagonals of the bridge and observing the deflection of a suitable instrument so
arranged as to indicate the relation between the artificial variation of the current
flowing in the one diagonal of the bridge and the variation ensuing in consequence
thereof in the current flowing in the other diagonal of the bridge, which deflection
will be a direct measure of the resistances to be determined, substantially as
described and illustrated by the accompanying diagrams
2 For the purpose of determining the value of an electrical resistance combined
with unknown electromotive forces, the combination with a Wheatstone budge
connection, the resistance to be measured forming a lateral bianch, thereof, of
suitable means for artificially varying the current in one of the diagonals, and of a
galvanometer or electrodynamometer consisting of needle or swinging coil
influenced by two fixed coils or ets of coils the magnetic field of one of which is
excited by the current variations in the one diagonal of the bridge, that of the
other by the current variations in the other diagonal of the bridge, the deflection
of the needle consequently being a direct measure of the ratio between these
curient variations, substantially as described and illustrated
3 In combination with a Wheatstone bridge connection, a pan of suitable
tiansformers the primary coils of which are inserted in the diagonals of the bridge,
while their secondary coils are connected with coils or sets of coils arranged so as
to create two magnetic fields cutting each other at right angles and influencing a
galvanometer needle or a swinging coil arranged between then fixed coils, or sets of
coils, so that the deflection of the needle or swinging coil is a measure of the ratio
of the simultaneous curent variations, as and for the purpose set forth
4 In combination with a Wheatstone-bridge connection, a pair of coils or set of
coils arranged so as to create two magnetic fields cutting each other at right angles
and influencing a galvanometer needle or swinging coil arranged between these
coils or sets of coils which are inserted in the diagonals of the bridge connection so
that the deflection of the needle or swinging coil is a direct measure of the
resistance of one of the lateral branches of the budge connection, in case no
alternating currents are flowing therein, substantially as and for the purpose
set forth
Dated the 91st day of January 1896
ABEL & IMRAY,
Agents for the Applicants