Improvements in Electrical M. asuring Instruments.
Year: 1898

page_text: Date of Application, 8th Feb., 1898
Improvements in Electrical M. asuring Instruments.
I, ARTHUR CECIL HEAP, of "The Firs," Penn, Bucks, Electrical Engineer, do
hereby declare the nature of this invention to be as follows:-
This invention relates to the construction of electrical measuring instruments of
the electro-dynamometer type in such a manner that the range over which a single
instrument will measure is materially increased.
As made at present an electro-dynamometer has two essential parts; one consists
of two or more coils of wire suitably wound, and known as the field coils, and the
other consists of a similar coil also suitably wound and known as the swinging coil.
The field coils are fixed on the base of the instrument and the swinging coil is
pivotted in such a manner that it is free to turn on its axis in the space between
the two field coils.
When an electric current is passed through the coils, the swinging coil is caused
to turn by the action of the electro-dynamic force set up in the coils. The amount
of such movement for a given current passing in the coils is controlled by means
of springs or gravity and after calibration with a suitable standard is a measure of
the currents passing through the instrument. By means of a pointer, or mirror,
or otherwise, this movement can be read off on an index.
In an instrument as above described all the current to be measured must be
passed through the coils, and it is therefore only possible with one instrument to
measure such currents as its coils are capable of carrying without overheating.
Its use is consequently much restricted.
The object of this invention is to construct an instrument which shall measure
currents independently of the wires forming its field and swinging coils, thus
enabling a given instrument to measure a far greater range of current.
My invention consists in employing along with an instrument substantially as
above described and which I will call the indicating part of my instrument-
a standard resistance through which the main part of the current passes and the
ohmic value of which, I arrange according to the amount of the current which is
to be measured. Only a small portion of the current to be measured passes through
the indicating part of my instrument and I connect these two parts, viz.
the indicating part and the resistance part electrically as shunt to one another.
I supply several standard resistances having different current carrying capacities,
to work with the same indicating portion and by this means a single instrument
is capable of measuring a far greater range of currents than would otherwise be
the case.
My invention is applicable either to continuous or to alternating current meters,
and the instrument may be arranged either as an amperemeter or as a watt-
meter.
When the instrument is to be used as an amperemeter I connect the fixed and
moving coils electrically either in series or in parallel according to the purpose for

page_text: which the instrument is required, and these are connected as a shunt to the above
described standard resistance.
When the instrument is to be used as a wattmeter the fixed coils only are con-
nected in series or in parallel according to requirements and as a shunt to the
standard resistance; the pivotted coil has then a comparatively high resistance
placed in series with it and is connected across the source of electro-motive-force
at which the power is to be measured.
In order that changes of temperature may not appreciably affect the indications
of the instrument I arrange that the ohmic resistance of the standard and of the
coils is such that I am able to insert a comparatively high resistance made of
material having a low temperature resistance coefficient in series with the coils
and I also make my standard resistance of the same material.
When the instrument is to be used for the measurement of alternating electric
currents I wind the above series resistance non-inductively and I arrange that the
self-induction of the coils is small in comparison with the total ohmic resistance
of the coil circuit I also construct the standard resistance non-inductively.
By means of a suitable switching arrangement to the pivotted coil I connect it
either in series or in parallel with the fixed coils, or together with a high resistance
in series with it, to the source of electro-motive-force; the instrument can then he
used either as an amperemeter or as a watt-meter.
Dated the Ol 1
SYDNEY E. PAGE, Wh. Sch., Assoc. Memb. Inst. C.E.,
18, New Bridge Street, Blackfriars, E.C., Agent for the Applicant.
Improvements in Electrical Measuring Instruments.
I, ARTHUR CECIL HEAP, of "The Firs," Penn, in the County of Bucks, 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:-
This invention relates to the construction of electrical measuring instruments
of the electro-dynamometer type in such a manner that the range over which a
single instrument will measure is materially increased. As made at present an
electro-dynamometer has two essential parts, one consists of two or more coils of
wire suitably wound and known as the field coils and the other consists of a similar
coil also suitably wound and known as the swinging coil. The field coils are fixed
on the base of the instrument and the swinging coil is pivotted in such a manner
that it is free to turn on its axis in the space between the two field coils.
electric current is passed through the coils, the swinging coil is caused to turn by
the action of the electro-dynamic force set up in the coils. The amount of such
movement for a given current passing in the coils is controlled by means of springs
or gravity, and after calibration with a suitable standard is a measure of the
currents passing through the instrument. By means of a pointer, or mirror, or
otherwise, this movement of the swinging coil can be read off on a scale.
When an
In an instrument as above described all the current to be measured must be
passed through the coils, and it is therefore only possible with one instrument to
measure such currents as its coils are capable of carrying without overheating.
Its use is consequently much restricted.
The object of this invention is to construct an instrument which shall measure
currents independently of the wires forming its field and swinging coils, thus
enabling a given instrument to measure a far greater range of current.

page_text: My invention consists in employing along with an instrument substantially as
above described and which I will call the indicating part of my instrument-
a standard resistance through which the main part of the current passes and the
ohmic value of which I arrange according to the amount of the current which is
to be measured. Only a small portion of the current to be measured passes through
the indicating part of my instrument and I connect these two parts, viz.
the indicating part and the resistance part electrically as shunts to one another.
I supply several standard resistances having different current carrying capacities
and suitable resistances to work with the same indicating portion and by this means
a single instrument is capable of measuring a far greater range of currents than
would otherwise be the case.
My invention is applicable either to continuous or to alternating current meters
and the instrument may be arranged either as an amperemeter or as a watt-
meter.
When the instrument is to be used as an amperemeter I connect the fixed and
moving coils electrically either in series or in parallel according to the purpose for
which the instrument is required, and these are connected as a shunt to the above
described standard resistance.
When the instrument is to be used as a wattmeter the fixed coils only are con-
nected in series or in parallel, according to requirements, and as a shunt to the
standard resistance; the pivotted coil has then a comparatively high resistance
placed in series with it and is connected across the source of electro-motive-force
at which the power is to be measured.
In order that changes of temperature may not appreciably affect the indications
of the instrument I arrange that the ohmic resistance of the standard and of the
coils is such that I am able to insert a comparatively high resistance made of
material having a low temperature resistance coefficient in series with the coils
and I also make my standard resistance of the same material.
When the instrument is to be used for the measurement of alternating electric
currents I wind the above series resistance non-inductively and I arrange that the
self-induction of the coils is small in comparison with the total ohmic resistance
of the coil circuit. I also construct the standard resistance non-inductively.
By means of a suitable switching arrangement to the pivoted coil I connect it
either in series or in parallel with the fixed coils, or together with a high resistance
in series with it, to the source of electro-motive-force the instrument can then be
used either as an amperemeter or as a wattmeter.
In the accompanying drawings:
Fig. 1 is an end elevation, Fig. 2 a side elevation & Fig. 3 a plan view of the
indicating part of my instrument.
FC are the fixed coils and S C the swinging coil pivoted so as to be free to
move between the two fixed coils, the swinging coil S C carries a pointer P which
travels over a scale S and indicates the position of the coil. The coil S C moves
against the action of springs Q.
Fig. 4 is a side elevation of a standard resistance Fig. 5 is a side elevation of
another standard resistance which would have twice the current carrying capacity
of that shown in Fig. 4 and would work with the same indicating part that is to
say if the standard resistance in Fig. 4 is capable of carrying 50 amperes of current,
that in Fig. 5 would carry 100 amperes; and if the standard Fig. 4 was first con-
nected as shown diagrammatically in Fig. 6 to the indicating part and with
50 amperes passing produced the maximum deflection of the coil as shown by the
pointer P on the scale S Fig. 3, then if standard Fig. 5 was connected as shown in
Fig. 6 in place of standard Fig. 4 100 amperes of current would produce the same
deflection.
Fig. 6 is a diagram of connections of the indicating part and the standard resist-
ances when the instrument is to be used as a multiple range amperemeter. FC
FC are the fixed coils, SC is the swinging coil, these are shown connected
electrically in parallel; R is the non-inductive resistance above referred to, which

page_text: is made of some material having a low temperature resistance coefficient. T T₁, are
the terminals of the indicating portion of the instrument; S R, S, R₁,
S, R, are standard resistances having different current carrying capacities. The
total current to be measured passes into the standard resistance through the
cables CC, the indicating part is connected to the standard resistance by means
of leads L L₁, a small portion of the total current therefore passes through the
lead L to the non-inductive resistance R and then splits through the coils F C
SC F C and back to the standard resistance through L
Fig. 7 is a diagram of connections when the instrument is to be used as a
multiple range wattmeter. In this case the fixed coils F C F C only are con-
nected in parallel and in series with the resistance R, these being connected as in
the case of the amperemeter as a shunt to the standard resistances S R S, R, S, R₂
as required, the standard resistance being connected in series with the source of
supply G, the output of which it is required to measure, W W being the load;
the swinging coil S C is connected directly across the terminals of the source G
by means of leads d d d₂, through a non-inductive resistance B, the resistance of
which has different values bb, bb, according to the range of voltage required.
Fig. 8 is a diagram of connections of an instrument indicating part and resist-
ances, which can be used either as a multiple range ammeter or as a multiple range
wattmeter.
By means of a suitable switch P S the connections can be made either as in
Fig. 6 or Fig. 7; thus with a plug connection in a&i, the connections are exactly
as in Fig. 6 and with plugs in 12 & az, a and
being open the connections become
exactly as in Fig. 7.
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:
=
(1) The combination as described of an indicating portion and standard resist-
ance, connected electrically as shunts to one another, the indicating portion taking
only a small proportion of the total current to be measured.
(2) The combination as described of an indicating portion and several standard
resistances having different carrying capacities and ohmic resistance values, all
arranged to work to the same indicating portion.
(3) The combination as described of an indicating part and standard resistances,
the indicating part having a resistance of low temperature resistance coefficient in
series with it.
(4) The combination as described of an indicating part the field coils of which
are connected electrically as shunts to a standard resistance, and the swinging coil
connected through a suitable resistance to the source of electromotive force of
supply.
(5) The combination as described of an indicating part and standard resistance
part, the indicating part being supplied with a suitable switch, such that the swing-
ing coil may be connected electrically in parallel with the fixed coils or may be
entirely separated from them and connected through a suitable resistance directly
to the source of electromotive force of supply.
Dated this Eighth day of November 1908