Improvements in Instruments for the Measurement of Electric Currents and Electromotive Force.
Year: 1889

page_text: Date of Application, 23rd Mar., 1889
Complete Specification Left, 23rd ec., 1889-Accepted, 25th Jan.. 1890
PROVISIONAL SPECIFICATION.
Improvements in Instruments for the Measurement of Electric
Currents and Electromotive Force.
EMIL HENRI HUNGERBÜHLER and JOSEPH TORR TODMAN, both of 35 Queen
Victoria Street in the City of London Electricians do hereby declare the nature of
this invention to be as follows:-
-
Our Invention consists in Improvements in Instruments for the measurement of
Electric Currents and Electromotive force. Our object being to construct such
instruments in a more portable form than those in general use, and to remedy some of
their defects. Within a case of metal or other suitable material preferably of circular
shape we mount a solenoid, which is wound with relatively thick or thin insulated
wire depending upon whether the instrument is to be used for measuring current, or
difference of potential. A pivot carrying a pointer moving over a dial suitably graduated
is mounted centrally, and a volute or concentric hair spring is attached to it and
fastened to the case. Secured to the pivot mounted as described is a right angular
arm which carries or forms part of a segmental taper iron core which moves freely
within the solenoid and is exactly balanced by an adjustable counter balance or
equivalent attached to its axis. Two small buffer springs are mounted at the heavier
end of the core to prevent rupture of the instrument by sudden shock from too heavy
a current. Terminals suitably mounted are provided.
Although we have described our improvements as designed for, and more particu-
larly applicable to portable instruments such are equally suitable for instruments of
any desired size.
Upon connecting the wires conveying a current to the terminals the segmental
taper core mounted as described is sucked into the solenoid and the pointer attached
thereto indicates upon the calibrated dial the value thereof. The volute hair spring
attached to the pivot returns the same to the zero point when no current is flowing;
we employ this form of spring as it is more certain in action than the spiral form
usually employed in instruments of this class.
Dated March 22nd 1000
FRANCIS M. ROGERS,
Agent for Applicants.
COMPLETE SPECIFICATION.
Improvements in Instruments for the Measurement of Electric
Currents and Electromotive Force.
EMIL HENRI HUNGERBÜHLER and JOSEPH TORR TODMAN both of 35° Queen
Victoria Street in the City of London, Electricians do hereby declare the nature of
this invention and in what manner the same is to he performed, to be particularly
described and ascertained in and by the following statement:—
Our Invention consists in "Improvements in instruments for the measurement of
Electric Currents and Electro motive force," our object being to construct such
instruments in a more portable form than those in general use and to remedy some of
their defects. Within a case of metal or other suitable material preferably of circular
shape we mount a solenoid which is wound with relatively thick or thin insulated wire
depending upon whether the instrument is to be used for measuring current or
difference of potential. A pivot carrying a pointer moving over a dial suitably
graduated is mounted centrally, and a volute or concentric hair spring is attached to
it, and fastened to the case. Secured to the pivot mounted as described is a right
angular arm which carries or formis part of a segmental taper iron core which moves

page_text: freely within the solenoid, and is exactly balanced by an adjustable counterbalance or
equivalent attached to its axis. Two small buffer springs are mounted at the heavier
end of the core to prevent rupture of the instrument by sudden shock from too heavy
a current. Terminals suitably mounted are provided; Although we have described
our improvements as designed for and more particularly applicable to portable instru-
ments such are equally suitable for instruments of any desired size. Upon connecting
the wires conveying a current to the terminals the segmental taper core mounted as
described is sucked into the solenoid and the pointer attached thereto, indicates upon
the calibrated dial the value thereof. The volute hair spring attached to the pivot
returns the same to the zero point when no current is flowing. We employ this form
of spring as it is more certain in action than the spiral form usually employed in
instruments of this class.
To enable the construction and operation of this instrument to be better understood
reference is made to the accompanying drawing in which :
Fig. 1, is a front view of the complete instrument.
Fig. 2, is a front view of instrument the cover being removed so as to shew
interior:
a
1, is the solenoid bobbin, which in this case is wound with thick wire 2; for measure-
ment of currentiasian ammeter. When required for measurement of electro motive
force this solenoid is wound with fine wire the length and resistance of which is
regulated by the range of reading required,the ends of the wire coil 2, are in either
case connected electrically with the terminals or binding screws 3,4. These terminals
or binding screws are constructed preferably as follows, so as to make the instrument
more convenient for the pocket. When out of use binding screw.4, occupies the
position shewn in fig. 1. within the hoop 5, a. screw hole being tapped in the head.of
binding screw 3, to receive it. When in use binding screw 4, is removed therefrom
and screwed into nut 6, which is insulated from the case A. . A pivot 7, carrying.
pointer 8, moving over a calibrated dial 9, is mounted centrally and a volute.or.con-
centric hair spring 10, is attached to it, its other end being fastened to, the case or
bobbin of solenoid. 1. Secured to the pivot 7, in any suitable manner is a right.
angular arm which either carries or forms part (as shewn, in the drawing) of a
segmental taper core of very soft iron 11, which moves freely within the bobbin of
solenoid 1, and is balanced by an adjustable counterbalance 12; attached to pivot. 7.
Two small buffer springs 13, are mounted at the heavy end of core to prevent rupture
or damage of the instrument by sudden shock from too heavy a current. To keep the
pointer 8, steady when the instrument is out of use, a stop 13, is pivoted in the
upper cover carrying glass, as shewn in fig. 1.
The hoop 5, figs. 1 and 2, enables the binding screw 3, to be screwed upon or
unscrewed from the nut 14, for the insertion of the wire. carrying a current see
fig. 2.
The operation of the instrument described is as follows:-
The leads or wires carrying the current are connected to terminals or binding
screws 3, 4 the stop 13, being first turned round sufficiently to release the pointer. 8.
By the action of the current circulating round the wire 2, upon solenoid bobbin 1;
the taper iron core 11, is sucked into the hollow space within the bobbin, to ans
extent depending upon the current flowing, its value in amperès volts or equiva
lent being shewn by the pointer 8, upon calibrated dial: 9.
just
We do not confine our improvements entirely to portable instruments as..
described; the same; devices may be mounted upon instruments- of. the::fixed..type,
and capable of measuring currents of considerable volume.
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 :
↑
.
1st: The combination intor with a portable instrument for measurement...of
current or electromotive force of a taper soft iron core pivoted centrally-so-as to
move freely within the curved bobbin of a solenoid, round the coils of which the

page_text: current to be measured flows, the pointer secured to the pivot with the volute or
concentric spring and counterbalance, and the buffer springs attached to the core
all combined and operating together for the purposes set forth.
2nd. The combination in or with a portable instrument for measurement of
electric current or electro motive force of the particular construction and arrange-
ment of binding screws, or terminals-operating as described.
Dated Deconsher 22-1 1000
FRANCIS M. ROGERS,
Agent.