INSTRUMENTS FOR TESTING ELECTRICAL CABLES
Year: 1884

page_text: PROVISIONAL SPECIFICATION.
I, JOSIAH LATIMER CLARK, of 6 Westminster Chambers in the City of
Westminster, Civil Engineer, do hereby declare the nature of said Invention for
" which
"IMPROVEMENTS IN
invention has been in part communicated to me from abroad by Henry C. Mance
of Kurracheo India, to be as follows:-
INSTRUMENTS FOR TESTING
ELECTRICAL CABLES
Our Improvement consists in the construction of a form of combined electrical
"Bridgo" and of resistance coils specially adapted for measuring in the most
perfect and convenient manner the distance of a fault in a submarine cable or land
lines (by the method known as Manco's method of testing faults). In order to
make this test in the most efficient manner, we construct a Wheatstone bridge
furnished with suitable pairs of resistance coils, usually in the proportions of
10-100 and 1000 ohms and we combine therewith a set of resistance coils of the
ordinary construction, and we arrange a key or handle in such a manner that tho
conducting wires leading to the galvanometer, the cable, and the earth, may be
instantaneously switched or turned from the 100-ohm pair of coils to the 1000 ohm
coils or vice versa, or from the 10 ohms to the 100 or the 1000 ohms, or to any.
other combination that may be found desirable for making the test in question.
1884.
J. HENRY JOHNSON,
47, Lincoln's Inn Fields, London, W.C.,
Agent for the said Josiah Latimer Clark,

page_text: COMPLETE SPECIFICATION.
I JOSIAH LATIMER CLARK of 6 Westminster Chambers in the City of
Westminster Civil Engineer, do hereby declare the nature of the said Invention
for IMPROVEMENTS IN INSTRUMENTS FOR TESTING ELECTRICAL CABLES, (in part
a communication to me from abroad by Henry C. Mance of Karachee India
and in part Invention made by me the said Josiah Latimer Clark) and in what
manner the same is to be performed, to be particularly described and ascertained in
and by the following statement :—
The object of this invention is to provide a better form of apparatus for taking
tests in accordance with "Mance's method for Eliminating the disturbing effects
which polarization and Earth currents produce during Electrical measurement."
In working this method much depends on being able between two tests to
quickly substitute in the testing bridge one set of proportion coils (A. B. fig 3)
of fixed value for another set, also of fixed value, but lesser or greater than the
first, meanwhile rapidly readjusting the resistance in the branch R fig 3 so as to
reproduce balance.
According to this Invention this difficulty is surmounted by using an improved
form of proportion coil box, wherein the different sets of coils can be instan-
taneously switched in and out of circuit by means of a double contact arm
operated by a handle so as to give a rotatory movement to the said arm the
contacts of each set being simultaneously made by the one movement of the
handle By this means the value of the branches A. B. (Fig 3.) in the Testing
Bridge can be instantaneously changed by a simple movement of the handle and
one couple of proportion cuils be substituted for another.
Three pairs of proportion coils are shewn in the drawings, the first having a
resistance of Ten-ohins the second a resistance of one hundred ohms and the third
a resistance of one thousand ohms in each coil. Other resistances may be used if
preferred to suit special circuits or modifications in the formula used in correcting
the tests.
Should other combinations in the proportion coils be desired the arm can bo
placed at zero and the proportion box be used in the ordinary manner by means of
two metal plugs only-or the arm can be constructed in two pieces one of which
being removed the required coil on one side can be connected by a plug and the
coils on the opposite side be thrown in and out of circuit by turning the handle-
or the two halves of the arm can be clamped at any required angle so that coils of
unequal value on either side can be switched in and out of circuit to suit particular
work or formulae used in connection with "Mance's method."
To facilitate the restoration of balance after the proportion coils have been
changed during a test there is added to the bridge a small box of single ohms
which can be thrown in or out of circuit by means of sliding contacts.
DESCDIDTION AND

page_text: this is familiar to every Electrician the details of its construction are not shewn―
In direct connection with it and practically forming part of it is the additional
box B containing any convenient number of coils of small resistance (generally
1 ohm each will be found most convenient) with sliding contacts for rapidly
effecting the finer adjustments-These coils are thrown in or out of circuit by
turning the handle H
The improved proportion box C fig 4. permits of the various pairs of coils being
instantaneously changed by giving a movement of rotation to the handle operating
the double arm It can be used in the ordinary manner with equal or unequal
proportions by placing the handle at zero as in fig 1. and inserting two metal
plugs K at the holes pertaining to the coils it is required to use The proportion -
coils may be short circuited if required by placing these two plugs in the two
extra holes near the terminals e and f-Two stops are provided for limiting the
play of the arm i when working by "Mance's method" these stops can be placed
in holes conveniently placed about the brass plate c.
The Limb or arm i is preferably furnished with platinum contact edges or points
to ensure perfect contact they rubbing on platinum surfaces in the metal blocks a, a,
In fig 1 the coils are drawn outside the box to show dingrammatically the manner
in which the connections are made-One end of each coil is in permanent connec-
tion with its insulated block, and the other end is brought to the common
terminals d¹ and d-tho arm i is in perfect metallic contact with the plate c and
terminal b.
"
At C in fig 4. the arm i is shewn in position for throwing a pair of one
hundred ohm proportion coils into circuit-It is obvious that coils of any required
resistance may be substituted for the pairs of Ten-one hundred and one thousand
ohms.
Fig. 2 is a section of the improved arrangement for manipulating the proportion
coils The arm i is shewn in the same position as in fig. 4.
Having now particularly described and ascertained the nature of our said
Invention and in what manner the same is to be performed we declare that what
we claim is
For use in testing electric cables a proportion box wherein the contacts between
the coils or resistances of one set can be simultaneously made and instantaneously
changed to another set by means of a double arm capable of having a rotatory
movement imparted to it so as to permit of the required tests being taken with the
rapidity and precision necessary for the proper use of the hereinbefore named
Manco's method of testing substantially as hereinbefore described.
Dated this fourth day of November 1884.