IMPROVEMENTS IN INSTRUMENTS CALLED " AMMETERS," VOLTMETERS," "POWERMETERS," AND OHMMETERS
Year: 1883

page_text: PROVISIONAL SPECIFICATION left by Frederik Vilhelm Andersen at the
Office of the Commissioners of Patents on the 4th December 1883.
" is
FREDERIK VILHELM ANDERSEN of Greenwich in the County of Kent, Electrical
Engineer "IMPROVEMENTS IN INSTRUMENTS CALLED " AMMETERS," VOLTMETERS,"
"POWERMETERS," AND OHMMETERS,"
"
The object of this invention is to construct an instrument or instruments for
measuring the strength of a current of electricity in "Ampêres," the electromotive
force in "Volts," the product of Ampêres and Volts in "Watts" and the resistance
in "Ohms."
It is a principle of electro magnetism that a straight bar magnet (steel magnet
or electro magnet) tends to revolve on its axis if a current of electricity flows
through one of its ends in a direction parallel to the axis of the bar, and that this
tendency to revolve is magnified if another current flows through the other end of
the bar magnet also parallel to the axis of the same and in opposite direction to the
first.
"
t
On this principle I have constructed a universal electricity-meter, that is to say an
instrument which measures "Ampêres," "Volts," "Watts" and Ohms," after
having by experiments discovered two, as far as I am aware, hitherto unknown
facts namely:
:-
1) that the tendency to revolve on the part of the bar-magnet is obtained not only
if currents flow through the bar itself as described above, but also if currents are
being passed through fixed conductors placed parallel with the axis of the bar
magnet, this being then made in the shape of a cylindrical tube inside which
the said conductors are placed without being mechanically connected with the
same.
2) that the tendency to revolve on the part of the bar magnet made of soft iron
and magnetised by means of currents of electricity passing through magnetising
solenoids is obtained on the principle described above (that is to say the passing
through the two ends in opposite directions) not only if the magnetising solenoids
are fixed to the soft iron bar but also if these solenoids are fixed independent of
the bar and without being mechanically connected with the same.
I will here describe the main parts of the instrument which I have constructed
on the above described principle developed according to the two facts discovered
ho ma

page_text: a, I provide a straight cylindrical iron tube which has a large lateral oval
opening cut out at its centre. This tube is suspended with its axis in a vertical
line by means of a metallic wire placed in the axis of the tube and fixed to the same.
b, I also provide one or more fixed conductors of copper or brass placed so as not
to touch the said iron tube and arranged so as to form circuits through the two
ends of the said tube. This may be obtained by carrying the said conductors into
the opening of the iron tube through the large oval opening cut out at its centre
and letting them pass out of the tube at its two ends. These circuits through
which electrical currents always are made to pass in opposite directions according
to the principle described in the first part of this Specification, will hereafter be
called the deflecting circuits of the instrument.
c, There are also one or more straight cylindrical solenoids or coils of conducting
wire placed round the said iron tube concentric and parallel with the same. The
inside diameters of these coils are larger than the outside diameter of the said iron
tube and the coils are fixed to the frame of the instrument in such a way that they
do not touch the iron tube. The circuit formed by the wires of these coils will
bereafter be called the magnetising circuit of the instrument.
d. There is also a pointer fixed to the outside surface of the suspended iron tube
at right angles to the axis of the same and a scale divided into degrees of a circle
and fixed to the frame of the instrument in a plane parallel to the pointer so as to
show the degrees of deflection or oscillation performed by the said iron tube and
the pointer.
To use the instrument for electrical measurements a current of electricity is made
to pass through the magnetising circuit described under the head c. this current
having the effect of maguetising the suspended iron tube or to call forth a
magnetic south pole in one end of the tube and a magnetic north pole in the
other end of the same tube. At the same time, parts of the same electrical
current or other currents are made to pass through one or both of the
deflecting circuits described under the head b these currents having the effect of
producing in the suspended iron tube a tendency for this tube to revolve on its
axis. Now, the tube being suspended in the metal wire is free to move for part of
a revolution, its revolving motion being limited by the conductors passing through
the lateral opening counteracted by the resistance exerted against torsion by the
suspending wire. The tube will therefore when the currents are flowing in its
circuits, oscillate to a number of degrees or angle of a circle at which the described
electro magnetic action balances the mechanical counteraction of the suspending
wire, this oscillation being accompanied by corresponding deflections of the pointer
over the scale. If the currents are kept flowing through the circuits of the
instrument for some time, then the oscillation will stop and the tube and the pointer
come to rest at a certain deflection while when the currents cease to flow the metal
wire will relieve itself of torsion bringing the tube and the pointer back to the
normal or zero position. The amount of deflection obtained in each case can be
taken as measures of the electro magnetic forces set up in the circuits of the
instrument.
When the instrument has to act as an Ammeter, then the magnetising circuit as
well as the deflecting circuits are formed of thick conductors and the whole current
the strength of which is to be measured in Ampères passes the different circuits in
two branches, each branch passing through one deflecting circuit and half the length
of the magnetising circuit in series.
When the instrument has to act as a Voltmeter then the circuits are all formed
of coils of thin conducting wire introducing at the same time a great length of wire
and high resistance.
When used as a Powermeter the instrument has the magnetising circuit formed
of fine conducting wire, through which a weak current, derived in shunt off the
electrical circuit of which the Volt Ampêres or Watts are to be measured magnetises
the iron tube while the main current of the same circuit acts in the deflecting
circuits, these being constructed as for the Ammeter.

page_text: When lastly used as an Ohmmeter the combination will be the same as described
above for the Ammeter with one or more additional deflecting circuits formed of
coils of fine wire. The main current passes through the complete Ammeter-
combination and a weak current derived from two points in an electrical circuit,
the resistance between which two points is to be indicated by the instrument,
passes through the added fine wire deflecting circuits.
Now the same instrument can be made so as to contain deflecting circuits made
of thick conductors for strong currents and other deflecting circuits made of fine
conductors and of high resistance for weak currents and also so as to contain a
magnetising circuit formed of thick conductors and another magnetising circuit
formed of fine conductors and thus by means of a combination of more terminals
fixed to the base of the instrument and to be used differently for different purposes
the saine instrument can be made to contain or combine all the four above mentioned
instruments in one so that merely by making use of the respective terminals for
each case the same instrument will serve as "Ammeter," "Voltmeter," "Powermeter"
or "Ohmmeter" respectively and forming a universal electricity-meter.
Although one instrument can be made so as to contain all the four instruments
I may also make instruments to serve for one purpose only, one instrument to
serve as an Ammeter only, another to serve as a Voltmeter only and so on.
Regarding the practical construction of my invention I also remark that I do not
limit myself to make use of the principle in exactly the same details given above which
serve merely for an illustration of the principle. For instance: the iron tube may
have two lateral slots instead of one cut out at the centre, the conductors forming
the deflecting circuits may be substituted by a single conductor in the shape of a
tube placed inside the movable iron tube and parallel with the same.
I may also construct the instruments with only one deflecting circuit namely a
deflecting circuit formed by means of a single straight conductor through one end
of the suspended iron tube, while the other end of the same tube is split into a
number of narrow strips which are bent outwards and arranged in a plane
perpendicular to the axis of the tube by this arrangement the lateral slot is
dispensed with.
The suspending of the iron tube may be made by other means than the metal
wire mentioned and the counteracting force be obtained in another way than as
torsion for instance by means of a helical or spiral spring or by some application of
the power of gravity. It is not necessary that the iron tube should be placed in a
vertical position. Instead of introducing the conductors for the deflecting circuits
through a slot cut out in the iron tube, a connection through this tube might be
obtained by means of mercury contacts whereby the tube would be free to move
round the whole circle.