An Improved Apparatus for Measuring the Resistance and Insulation of Electric Conductors.
Year: 1890

page_text: Date of Application, 22nd Nov., 1890
Complete Specification Left, 13th July, 1891-Accepted, 12th Sept., 1891
PROVISIONAL SPECIFICATION.
An Improved Apparatus for Measuring the Resistance and
Insulation of Electric Conductors.
We WILLIAM ARTHUR PRICE and WILLIAM ERNEST GRAY, both of
Silvertown in the County of Essex, Electricians, do hereby declare the nature of
this invention to be as follows:-
The object of this invention is to provide a compact and portable apparatus for
imaking reliable and complete tests, both for resistance and insulation, upon electrical
installations and circuits generally.
In place of the detached galvanometer hitherto employed, we now propose to
place it in the resistance box, and to provide an adjustable magnet which shall
control the galvanometer needle, and facilitate the setting of the same to zero.
Instead of an astatic galvanometer, we use one fitted with a single ordinary
compass needle carrying an index hand or pointer. A bar magnet mounted in the
side of the containing box, serves to control the needle, which, when adjusted
roughly to north and south, by shifting the box for the purpose, may be brought
to zero, by adjusting either the north or the south pole of the magnet in relation
to the north pole of the needle. This adaptation of the magnet to the galvanometer
also enables the electrician to increase or diminish the intensity of the field in
which the needle swings, by placing, at his option, the north or the south pole of
the magnet uppermost.
The conductor of the electrical circuit to be tested is connected to the combined
instrument in the usual way, and the instrument is provided with the necessary
shifting plugs for changing the connections of the resistance' coils in the ordinary
manner.
Dated this 21st day of November 1900
NEWTON & SON,
Agents for the Applicants.
COMPLETE SPECIFICATION.
An Improved Apparatus for Measuring the Resistance and
Insulation of Electric Conductors.
We WILLIAM ARTHUR PRICE and WILLIAM ERNEST GRAY, both of
Silvertown, in the County of Essex, Electricians, 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:—
The object of this invention is to provide a compact and portable apparatus for
making reliable and complete tests, both for resistance and insulation, upon
electrical installations and circuits generally.
In place of the detached galvanometer hitherto employed in connection with
portable testing apparatus, we now propose to insert it in the resistance box, and
to provide an adjustable magnet which shall control the galvanometer needle, and
facilitate the setting of the same to zero.
Instead of an astatic galvanometer, we use one fitted with a single ordinary
compass needle, carrying the index hand or pointer. A bar magnet mounted in
the side of the containing box, serves to control the needle, which, when adjusted
roughly to north and south, by shifting the box for the purpose, may be brought
to zero, by adjusting either the north or the south pole of the magnet to the north
pole of the needle.

page_text: In order to explain more clearly the nature of our invention, we have shewn in
the accompanying drawing our improved resistance box in plan view at Fig. 1,
arranged for testing the resistance of a cable.
Fig. 2 is an elevation of the box, showing the position of the controlling
magnet.
As the nature of this apparatus and the mode of working it, is well known to all
practical electricians, it will only be necessary to refer to the principal parts of
the instrument, and shew its connection with the battery and the wire to be tested,
to make the character and merits of our invention clear.
A is the ordinary Wheatstone bridge, in which the current from the battery is
divided, one portion going to the cable to be tested, and the other through the
dials B, C, back to the battery. D is the key for passing a portion of the divided
current through the galvanometer E, the coil of which is connected with the
block e on one side of the galvanometer, and with the block e¹ on the other side,
which blocks may be considered as the terminals of the galvanometer coil.
F, F are the ends of the cable to be tested, the same being secured to the
terminals The terminal connects with the Wheatstone bridge, and the
terminal with the battery socket g. G G¹ are the leads from the battery,
the plug of one being in the socket g, and the plug of the other (connected, say, to
the positive pole of the battery) fitting the socket g', which socket connects with the
centre block a of the Wheatstone bridge. The current admitted to the gal-
vanometer E by the depression of the key D, after actuating the needle, as usual,
passes off by the block ¹ to the cable, and through the cable back to the battery.
H is a bar magnet recessed into the side of the box, and carried by a centre
pivot pin, on which it is free to turn. This magnet is placed opposite the north
pole of the galvanometer needle, and by its attraction or repulsion, it serves to
set the pointer accurately to zero, and give it a tendency to retain that position.
This adaptation of the magnet to the galvanometer also enables the electrician
to increase or diminish the intensity of the field in which the needle swings, by
placing, at his option, the north or the south pole of the magnet uppermost, the north
pole, when uppermost, serving to decrease the intensity of the magnetic field, and the
south pole, when brought uppermost, producing the opposite effect.
For testing the insulation of a cable, it will only be necessary to readjust the
resistance box in the manner well known to electricians, and the readings of the
instrument may then be taken as usual.
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 :-
The arrangement of portable testing apparatus above described, in which the
galvanometer is controlled by the action of an axially adjustable bar magnet.
Dated this 9th 1an of Tulu 1001
NEWTON & SON,
Agents for the Applicants.