Improvements in Electrical Measuring Instruments.
Year: 1899

page_text: Date of Application, 22nd Nov., 1899
Complete Specification Left, 18th June, 1900-Accepted, 6th Oct., 1900
PROVISIONAL SPECIFICATION.
Improvements in Electrical Measuring Instruments.
I, LLEWELYN BIRCHALL ATKINSON, of The Testing Works, Harrowby Lane,
Cardiff, Civil Engineer, do hereby declare the nature of this invention to be as
follows;
-
This invention relates to improvements in electrical measuring instruments.
and has for its object the production of cheap and accurate instruments, for
measurement of electromotive force, current, and power.
This invention consists in constructing a floating body adapted to float and
move in a liquid, and being capable of being acted upon by a coil or coils carry-
ing the electric currents to be measured. Various forms may be used but the
following are some of those best adapted for the purpose. A glass bulb or float
with a counterbalance and stem, as used for the purpose of an hydrometer, has
in it a soft iron wire or hardened steel magnet.
This float is placed in a glass tube closed at the bottom, and preferably at
the top, and surrounded by a coil carrying the current to be measured. The
height at which the float stands is an index of the current being measured. In
certain cases there may be two liquids which do not mix, and the stem passes
in moving out of one liquid into the other, and in this case the float may be
at the top and the stem at the lower part of the instrument, the result being a
rather more stable balance. The reading may be made in various ways but I
prefer to have a line or mark surrounding the float, so that it is in close proximity
to the outer tube, on which, or attached to which, the scale is. In certain cases
where it is desirable to make the movement very slow, I make the float closely
fit the tube only allowing a thin layer of liquid to intervene, and in this case
the liquid may be coloured and the float white, when by giving the latter a
defined edge, the appearance is that of a dark liquid column in the tube, by
which the readings may be effected. The scale afforded by such an instrument
may be made, in the case of an ammeter, nearly proportioned to the current, or
in a voltmeter, where it is necessary or desirable to only measure a short part of
the whole range, this may be effected by either putting the end of the magnetic
wire at such a distance from the end of the coil, that the current must reach a
determined limit before the movement commences; or by so weighing the float
that it rests on the bottom of the containing tube, and only lifts when the
current reaches the determined limit, at which it is desired that the readings
should commence, when the whole travel will be completed with a small additional
current. Since the zero. at which the float will rest, depends on the density of
the liquid, and is therefore affected by the temperature of the liquid, involving
normally a change of zero with change of temperature, I provide the following
means of obviating this difficulty. A bulb or lengthened tube is provided con-
taining sufficient liquid to furnish, by its expansion, a variation in level of the
liquid in the tube, corresponding to, and counterbalancing the variation in the
position of the float, due to change of density. Or where the zero reading can
be taken conveniently before the working reading, I provide means for varying

page_text: the position of the tube relative to the scale and coil, so that the zero is corrected
in this manner. Where the correction is to be made in this way, without a zero
reading being taken, I fix to the scale a thermometer, whose column varies in
height correspondingly to the variation of the level of the float, and a fixed line
being provided on the tube, this line is to be moved to the level of the ther-
mometer column.
In another method of compensation, I saturate the solution with a salt much
more soluble in hot than cold water, so that the amount dissolved increases, and
the density of the solution thereof, as the temperature rises.
Whilst I have described the use of glass tubes and floats, it is understood that
metal or other materials may be substituted, and whilst I have found water, if
pure, and in a clean glass vessel, to be a very suitable liquid, other liquids such
as ether, chloroform, carbon disulphide, tar oils, etc. may be used, either alone,
or in combination with water or one another, or water containing salts, as zinc
sulphate, zinc bromide, etc. to vary its density, may also be used with advantage
in certain cases. The instrument described may be used as a maximum demand
indicator, by making the float closely fit the tube, when the motion may be as
slow as desired; and to record the maximum movement, I provide that the stem
should be so related to the liquid that the maximum movement is shown by a
stain or mark on the stem. Thus if the stem is of glass, the liquid may be
covered with a non-evaporating oil, which wets the glass, or the stem may be
of Semiporous material, and the liquid coloured, and in this case the stem may
be removable so as to form a permanent record of the movement.
Dat
00
1
Improvements in Electrical Measuring Instruments.
I, LLEWELYN BIRCHALL ATKINSON, of The Testing Works, Harrowby Lane,
Cardiff, Civil Engineer, do hereby declare the nature of this invention and in
what manner the same is to be performed to be particularly described and ascer-
tained in and by the following statement:-
This invention relates to electrical measuring instruments of a known principle
for the measurement of electromotive force or current, in which a
in sensitive and static equilibrium, in a liquid, is attracted and moved by the
floating body
electric current to be measured, traversing a coil or coils surrounding the said
floating body; and consists of improvements whereby the sensitiveness of the
indication is increased by a combination of liquids and correctness is ensured
by automatic and hand compensation being introduced for correction of readings
caused by variation of external temperature.
The device is exceedingly sensitive and accurate and can be manufactured and
produced at a trifling cost either as an ammeter, a voltmeter for definite ranges,
or as a maximum current recording instrument.
And in order that my invention may be the better understood I now proceed
to describe practical forms of carrying the same into effect, reference being had
to the drawings hereto annexed and to the letters and figures marked thereon.
Figure 1 shows the inner tube detached, with two internal liquids and the
coil in diagram.
Figure shows the floating body and coil inverted.
"
Figure 3 shows the floating body removed with paper index line.

page_text: Figure 4 shows a modification in which part of the floating body almost fills
the containing tube, and an addition to liquid to maintain uniform density at
varying temperatures.
Figure 5 shows my device with modification to give compensation of liquid
at varying temperatures.
Figure 6 shows my device with attached thermometer and hand adjusted
scale.
For the floating body of my device I use an ordinary hydrometer bulb A with
a long stem a and counter balance a¹ for stability when the bulb is used with
the stem upright. Within this hydrometer bulb is fitted a soft iron or steel or
hardened steel wire B running axially nearly the whole length of the bulb.
This bulb or float is placed in a glass tube C closed at the bottom and at the
top, containing a liquid D with air space above, or completely filled with two
liquids D D of different density, which do not mix, to give greater sensitiveness
to the floating bulb.
About that part of the glass tube C that contains the stem of the float or into
which the stem passes is placed a coil or coils of wire E carrying the current to
be measured.
An index line F is marked on the float A either by engraving, by paint, or
by an impressed line on a waterproof paper F¹ (Figure 3) or in other convenient
manner; or the body of the float A may be made with horizontal defined ends,
as in Figure 4, and either of these ends may be used as an index line.
A graduated and calibrated scale G is applied in front with a central slot, or
at the sides of the tube C, upon which the indication of the index mark F of the
float A may be read.
The float A, when no current is passing remains in sensitive but static equili-
brium of floatation, with its index mark F at zero on the scale G. When the
current passes through the coil E the attraction of the solenoid, so formed,
attracts the soft iron or steel magnet wire B of the float A, and thus disturbs
the normal equilibrium of floatation, and the amount of such disturbance and
movement may be read by the index F upon the scale G.
In order to make the alteration of buoyancy of the bulb A exceptionally sensi-
tive, two liquids are used, which are of different density, and will not mix, as
in Figure 1. Such liquids may be oil and water ether and water and carbon-
disulphide and water.
'
In this case the float A and the coil E may be inverted as in Figure 2 making
the float in stable equilibrium without a counter balance weight."
In certain cases, where it is desirable to make the.movement of the float A
very slow, I may make the float to closely fit the tube as in Figure 4. only
allowing a thin layer of liquid to intervene and in this case the liquid may be
coloured and the float white and opaque, when by giving the body of the latter
a defined and horizontal edge, the appearance is that of a dark liquid column in
the lower part of the tube, with a lighter column above it, the upper edge of
the dark column being the index level for reading on the scale.
The scale afforded by such an instrument may be made, in an ammeter, nearly
proportioned to the current, or in a voltmeter, where it is necessary or desirable
to only measure a short part of the whole range, this may be effected by either
putting the end of the magnetic wire at such a distance from the end of the
coil, that the current reaches a determined limit before the movement com-
mences; or by so weighting the float that it rests upon the bottom of the contain-
ing tube, and only lifts when the current reaches the determined limit.
Since the point of equilibrium at which the float will rest depends on the
density of the liquid and is therefore effected by the temperature of the liquid,
involving normally a change of zero with a change of temperature, I provide
the following means for obviating this difficulty.
I fill the tube as in Figure 4 with a solution of a salt much more soluble in
hot than in cold water, such as ammonium sulphate or ammonium chloride, with

page_text: which the solution is saturated, and of which a residue of undissolved salt H
remains in contact with the water at the bottom of the tube. By this means
the density of the liquid of floatation may be kept constant through all climatic
variations of temperature.
Or, I may provide, as in Figure 5, an extension of the tube, in the form of a
bulb H, or it may be a separate vessel connected with the tube, containing such
a bulk of liquid that the liquid in the bulb or vessel, in expanding, raises the
surface of the liquid in the tube by the amount which the hydrometer falls due
to the variation in density of the liquid.
For the same purpose, I may provide a hand adjustment of the scale to zero
as in Figure 6. In this case I provide a thermometer K adjoining and fixed
to the containing tube C by metal straps L.
The scale plate G is also adapted to slide by a metal strap M upon the 'tube C
and carries an index pointer N which must always be adjusted to the top of the
collumn of inercury in the thermometer K so that the zero of the scale is thereby
adjusted to variations of temperature before the reading is taken.
Though I have described the float as conveniently of glass it is to be understood
that metal or other materials may be substituted, and though I have found water,
if
f pure and in a clean glass vessel, to be a very suitable liquid, other liquids such
as ether, chloroform, carbon-disulphide, tar-oils, and the like, may be used, either
alone, or in combination with water, or with one another.
To adapt my device as a maximum current recorder, I may adapt the stem to
the liquid, so that the maximum movement may be indicated by a mark or
stain on the stem where two liquids are used, and the stem, as the current
increases, enters into a distinct staining or marking liquid. In this case the stem
should be removable from the bulb.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what I
claim is:-
1st. In combination, in an electrical measuring device, an hydrometer bulb
and stem without counter balance; a magnetic metal rod therein; a transparent
containing tube; two liquids therein of different densities and unmixable, the
bulb being in the highest liquid of lighter density, and the stem being disposed
downwards; and a coil carrying the current to be measured surrounding lower
part of containing tube.
2nd. In an electrical current measuring device, consisting of a floating body,
operated by the magnetic attraction of the passing current, means for maintain-
ing the constant density under varying temperature of the supporting liquid,
consisting of a saturated solution of a salt, more soluble in hot than cold water,
and a further supply of said salt, such as ammonium sulphate or chloride, in
contact with said solution.
3rd. In an electrical current measuring device, consisting of a floating body
operated by the magnetic attraction of the passing current, means for hand
adjustment of the indicating scale to compensate for change of temperature, con-
sisting of a thermometer fixed adjacent to the hydrometer containing tube, a
sliding scale upon the hydrometer containing tube, and an index adapted for
adjustment of scale to level of thermometer column.
Dated th 19th low of Tune 1000
FELL & JAMES,
1, Queen Victoria Street, London, E.C., Agents for the Applicant.