IMPROVED INSTRUMENTS FOR DETERMINING OR MEASURING ELECTRIC CURRENTS AND ELECTRO-MOTIVE FORCE
Year: 1885

page_text: Currents and Electromotive Force.
I OCTAVIUS MARCH, of 53 Grafton Road, West Kensington Park, London, W. in
the County of Middlesex, Electrical Engineer, do hereby declare the nature of my
Invention for IMPROVED INSTRUMENTS FOR DETERMINING OR MEASURING ELECTRIC
CURRENTS AND ELECTRO-MOTIVE FORCE, to be as follows:-
The improvements referred to in the Title of my Invention include two main
types or descriptions namely, under the first head "Ammeters," and under the
second head "Voltineters."
The primary object of my invention is to produce instruments for measuring
electric currents which shall not only bo direct reading but also have a wide range
of reading; be casy of calibration and inexpensive to manufacture.
In the case of Ammeters I also so construct them in accordance with my
Invention, that they shall possess the further advantage of having, practically,
no resistance. The method of construction which I adopt is substantially as
follows-
Upon the upper surface of a bedplate of any suitable material, I cut a longi-
tudinal groove in which I place a rod of copper, having binding screws at either
end; and, at one end of said bed plate, above same, I arrange a magnetic needle
suitably suspended poised or pivotted and having adapted thereto a dial plate with
a suitable number of divisions formed radially thereon-I adapt to a slide over the
copper rod aforesaid a magnetic bar which is capable of being moved to and fro in
a longitudinal direction, and in a line parallel with the copper rod above referred
to, so that said magnetic bar can be placed at any distance from the magnetic
needle within the limits of the base or bed plate aforesaid-Now, on the current
being passed through the copper rod aforesaid (and the magnet having been
previously caused to recede as far as possible from the needle) the magnetic needle
will assume a position approximately at right angles thereto The magnet is then
advanced towards the needle until the deflection is reduced to a given number of
degrees, and, the value of the current passing through the copper rod aforesaid
will be indicated upon a scale formed upon the bedplate, by a pointer or index
attached to the sliding frame of the magnet-The various angles at which the
eedle would be brought to rest and the corresponding scales upon the bedplate
Грилл Са

page_text: will be determined by the range which the instrument constructed according to my
Invention is intended to have.
In order to ascertain at any time if the instrument above referred to is in
calibration I adopt the following means; That is to say. When the instrument
has been graduated, it is placed in such a position relatively to the Earth's
magnetic meridian that the needle stands at right angles to the length of the base
(the magnet having first been removed). The magnot is then placed in its slide
and made to approach towards the needle until it comes to rest at angle of 45°, the
position of the index or pointer is then marked. By repeating this operation at
any time, error arising from loss of power by the magnet is at once detected if the
magnet when placed in its marked position fails to bring the needle to its correct
place; and, such loss when it occurs can be speedily rectified by rubbing the
magnet upon another of sufficient strength and in such a manner as to make up or
restore the loss which may have occurred to the first named magnet.
With an instrument constructed as above described, a range of, reading of, from
1 to 50 ampères is readily obtainable. Where however a still greater range than
that aforesaid is required, I necessarily modify the arrangement adopted as regards
its details but without departing from the main or essential features distinguishing
the first named arrangement above described, and, said modified arrangement
I purpose describing fully in the Complete Specification of my present Invention.
I construct a " Voltmeter according to my present Invention in a manner
similar generally to that described above and adopted in the case of "Ammeters
but instead of using the copper rod hereinbefore referred to, I substitute therefor
a suitably constructed and applied coil of fine wire of a suitable length and
possessing a suitable resistance."
"
As a modification additional to either of the two types or classes of instruments
above described, I also construct a combined Voltmeter, and Ammeter by including
the copper rod and coil respectively, aforesaid, in one instrument.
Instead also of placing the instruments aforesaid in a horizontal position, 1
may place them in a vertical position. In which latter case, I employ a suitably
pivotted needle, and may sometimes bend the copper rod hereinbefore referred to
so as to allow of its passing under and returning over the needle any desired
number of times. I also sometimes use an astatic pair, instead of a single needle.
. 1005

page_text: Currents and Electro-motive Force.
I OCTAVIUS MARCH of N° 53 Gratton Road, West Kensington Park, London, W.
in the County of Middlesex, Electrical Engineer, 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 improvements referred to in the title of my Invention include two main
types or descriptions, namely, under the first head, "Ammeters," and under the
second head" Voltmeters."
The primary object of my Invention is to produce instruments for measuring
electric currents which shall not only be direct reading, but also have a wide range
of reading; be easy of calibration and inexpensive to manufacture.
In the case of "Ammeters," I also so construct them in accordance with my
Invention, that they shall possess the further advantage of having, practically, no
resistance. The method of construction which I adopt is substantially as follows.
Upon the upper surface of a bedplate of any suitable material, I cut a longitudinal
groove in which I place a rod of copper or other suitable material, having binding
screws at either end; and at one end of said bedplate, above same, I arrange a
magnetic needle suitably suspended, poised or pivotted and having adapted thereto
a dial plate with a suitable number of divisions formed radially thereon. I adapt
to a slido over the copper rod aforesaid a magnetic bar which is capable of being
moved to and fro in a longitudinal direction, and in a line parallel with the copper
rod above referred to, so that said magnetic bar can be placed at any distance from
the magnetic needle within the limits of the base or bedplate aforesaid. Now, on
the current being passed through the copper rod aforesaid (and the magnet having
been previously caused to recede as far as possible from the needle) the magnetic
needle will assume a position approximately at right angles thereto.
is then advanced towards the needle until the deflection is reduced to a given
The magnet
number of degrees, and, the value of the current passing through the copper rod
aforesaid will be indicated upon a scale formed upon the bedplate by a pointer or
index attached to the sliding frame of the magnet. The various angles at which
the needle would be brought to rest and the corresponding scale upon the bedplate
will be determined by the range which the instrument constructed according to my
Invention is intended to have.
In order to ascertain at any time if the instrument above referred to is in
calibration I adopt the following means; That is to say, When the instrument
bas been graduated, it is placed in such a position relatively to the Earth's
magnetic meridian that the needle stands at right angles to the length of the base
(the magnet having first been removed). The magnet is then placed in the slide
and made to approach towards the needle until it comes to rest at one of the
divisions on the dial plate, usually the one forming an angle of 45°; the position
of the index or pointer is then marked. By repeating this operation at any time,
error arising from loss of power by the magnet is at once detected, if the magnet

page_text: when placed in its marked position fails to bring the needle to its correct place;
and, such loss when it occurs can be speedily rectified by rubbing the magnet upon
another of sufficient strength, and in such a manner as to make up or restore the
loss which may have occurred to the first named magnet
With an instrument constructed as above described, a range of reading of from
1 to 50 Ampères is readily obtainable. Where however a still greater range than
that aforesaid is required, I necessarily modify the arrangement adopted as regards
its details but without departing from the main or essential features. In such case
(namely where a considerably greater range is required) I proceed as follows,
I construct an instrument with two bed plates one over the other so connected
together with suitable hinges that the upper one may be raised from the lower ono
without losing its parallel position; the lower bed plate contains the bar of
copper or other suitable material and necessary binding screws, while the upper
bed plate contains the pivotted needle, magnetic bar slide, and scale. By this
means the measurement of much larger currents is practicable without increasing
the length of the instrument; as, by raising the needle from the bar conducting
the current, tho influence of such current upon the needle is reduced while the
power of the controlling magnetic bar is not interfered with. I find in practice
that it is convenient so to arrange the distance to which the upper bed plate is
raised that the readings of the scale (which is adjusted to its normal position) may
be multiplied by ten to give the correct reading in its raised position; that is, to
such a distance that the influence which the current passing through the copper
bar has upon the pivotted needle is reduced to one tenth.
I construct a "Voltmeter" according to my present Invention in a manner
similar generally, to that described above and adopted in the case of "Ammeters
but instead of using the copper rod hereinbefore referred to, I substitute therefor
a suitably constructed and applied coil of fine wire of a suitable length and
possessing a suitable resistance..
As a modification additional to either of the two types or classes of instruments
above described, I also construct a combined "Voltmeter" and "Ammeter," by
including the copper rod and coil respectively, aforesaid, in one instrument.
Instead also of placing the instruments aforesaid in a horizontal position, I may
place them in a vertical position. In which latter case I employ a suitably
pivotted needle, and may sometimes bend the copper rod hereinbefore referred to,
BO as to allow of its passing under and returning over the needle any desired
number of times. I also sometimes use an Astatic pair, instead of a single, needle.
Having now particularly described and ascertained the nature of my said
Invention and in what manner the same is to be performed I declare that what
I claim is
The improved instruments for determining or measuring Electric currents and
Electro-motive force substantially as herein described and set forth.
100