Improvements in Electric Supply Meters
Year: 1891

page_text: Date of Application, 14th Mar., 1891
Complete Specification Left, 10th Nov., 1891-Accepted, 12th Dec., 1891
PROVISIONAL SPECIFICATION.
Improvements in Electric Supply Meters
1. JOHN PERRY, Professor of Engineering, Fellow of the Royal Society, of
31 Brunswick Square, London, W.C. du inreby declare the nature of this inven-
tion to be as follows:-
In my Specification No. 873 of 1890 I describe a way of carrying out a principle
first enunciated in my Patent Specification No. 2642 of 1882. This principle is
that an electric motor either with permanent field magnets or shunt electro
magnets resisted in its motion mainly by Foucault currents gives a good supply
meter. In Specification 873 of 189) I described the armature of the electric
motor as consisting of metal forming a surface of revolution capable of rotating
about its axis which is vertical, bounded by two horizontal circular ring mercury
troughs so that current passing from one trough to the other through the armature
Thus
passes in the direction of generating lines in the surface of revolution.
there is the same kind of current all the way round. My present invention is an
improvement on the various forms described in that Specification. I have found
that when a solid dips into mercury there is a frictional resistance to motion, which
It is rather
is quite unlike the fluid resistance which everybody imagines it to be.
like the friction of one solid rubbing on another. To diminish it as much as
possible now take care that my armature shall be completely immersed in one of
the mercury troughs, only the spindle part of it emerging from this trough and
hence the frictional loss of energy in one revolution at this emerging part is small.
The spindle must now be larger, however, as it must convey the current & hence I
usually have it wholly or partly of copper. My second mercury trough is either
rotating, carried by the spindle & has a fixed conductor dipping into it as near the
axis of revolution as possible or it is a fixed mercury trough surrounding the
spindle & from the spindle a conducting part or lip overhangs into the trough.
In my Patent Specification No. 7219 of 1890 I have described another way of
getting over this difficulty due to quasi solid friction. But there I was compelled
to convey only part of my current by the conducting armature, the rest going by
In my present
the mercury as there were not two distinct bodies of mercury.
invention one body of mercury merely conveys current from a fixed conductor
to the moving armature, the other body of mercury takes away current and gives
it to another fixed conductor. And to be quite sure that there shall be almost no
forces acting on the mercury because of its conveying current, I usually coat my
armature with an insulating varnish or other covering except just at those places
where current is received & given out, that is, at the lips, or, as one of the lips is
now not necessarily a vertical adjunct to the armature; the edge of the armature
or a circular belt near the edge is left bare of varnish. This description will be
more readily understood if my Patent Specifications No. 873 of 1890 and No. 7219
of 1890 are read along with it as this improvement relates to all conducting
armatures there described.
A flat disc receiving current at its bare outer edge, immersed in mercury between
two flat magnetic poles (with or without discontinuities in the polar surfaces, to
produce Foucault current friction as described in the above Specifications) is the
form of armature which, at present, I consider to be best. In Fig. 3 of my Patent
Specification No. 7219 of 1890, if instead of allowing the mercury to be continuous
from d to we have an outer free surface at d and an inner free surface at & we
have a good form of my present invention.

page_text: If the iron of my electromagnet is well divided, these supply meters will register
alternating currents as well as continuous currents.
1. 1801
JOHN PERRY.
COMPLETE SPECIFICATION.
Improvements in Electric Supply Meters.
1, JOHN PERRY, Professor of Engineering, Fellow of the Royal Society of
31 Brunswick Square London W.C. do hereby declare the nature of this inven-
tion and in what manner the same is to be performed, to be particularly described
and ascertained in and by the following statement:―
In my Specification No. 873 of 1890 I describe a way of carrying out a principle
first enunciated in my Patent Specification No. 2642 of 1882. The principle is
that an electric motor, either with permanent field magnets or shunt electro-
magnets, resisted in its motion mainly by Foucault currents gives a good supply
meter. In Specification 873 of 1890 I described the armature of the electric
motor as consisting of metal forming a surface of revolution capable of rotating
about its axis which is vertical bounded by two horizontal circular ring mercury
troughs so that current passing from one trough to the other through the
armature passes in the direction of generating lines in the surface of revolution.
Thus there is the same kind of current all the way round. My present invention is
an improvement on the various forms described in that Specification. I have
found that when a solid dips into mercury there is a frictional resistance to motion
which is quite unlike the fluid resistance which everybody imagines it to be. It is
rather like the friction of one solid rubbing on another. To diminish it as much
as possible now take care that my amature shall be completely immersed in one
of the mercury troughs, only the spindle part of it, of a part of small diameter,
emerging from this trough and hence the frictional loss of energy in one revolution
at this emerging part is small. The spindle must now be larger, however, as it
must convey the current & hence that it may not be too large I usually have it
wholly or partly of copper. My second mercury trough is either rotating, carried
by the spindle & has a fixed conductor dipping into it in the axis of revolution or
as near the axis as possible or it is a fixed mercury trough surrounding the spindle
& from the spindle a conducting part or lip overhangs into the trough.
In my Patent Specification No. 7219 of 1890 I have described another way of
getting over this difficulty due to quasi-solid friction.
But there I was compelled to convey only part of my current by the conducting
armature, another portion going by the mercury, as there were not two distinct
bodies of mercury.
In my present invention one body of mercury merely conveys current from a
fixed conductor which may be in any part of the mercury & of any shape, to the
moving armature: the other body of mercury takes away current & gives it to
another fixed conductor. And to be quite sure that there shall be almost no forces
acting on the mercury because of its conveying current which ought to be passing
through the armature, I usually coat my armature with an insulating varnish or
other covering, except just at those places where current is received & given out,
that is, at the lips; or as one of the lips is now not necessarily a vertical adjunct
to the armature, the edge of the armature or a circular belt near the edge is left
bare of varnish. If current passes down through the mercury before entering at
the lip of the armature the mercury tends to move in an opposite direction to the
motion of the armature & so retards it & sometimes I prefer this to be the case.
This description will be more readily understood if my Patent Specifications
No. 873 of 1890 and No. 7219 of 1890 are read along with it as this improvement
relates to all conducting armatures there described & the improvement consists in

page_text: doing away with the quasi-solid friction experienced at the surfaces of the mercury
cups in the instruments described in No. 873 of 1890.
A flat disc receiving current at its bare outer edge, immersed in mercury between
two flat magnetic poles (with or without discontinuities in the polar surfaces to
produce Foucault current friction as described in the above Specifications) is one
form of the armature. The current may be supplied to the mercury & outer lip of
the disc by an outer ring conductor or by a conductor entering near the centre.
In Fig. 3 of my Specification No. 7219 of 1890 if instead of allowing the
mercury to be continuous from d to we have an outer free surface at d & an inner
free surface at we have a good form of my present invention. If the iron of my
electromagnet is well divided these supply meters will register alternating currents
as well as continuous currents.
I have experimented with many forms of my invention, with plane, conical &
other polar surfaces. The form which now seems best is shown in Figures 1,
2 & 3.
Fig. is a section through the axis N N, P M S is a tubular magnet wound
with wire W, through which a nearly constant current passes, say, under the
constant voltage of the supply leads. If the iron is nearly saturated, inagnetically,
a slight change of veltage produces practically no change in the constant of the
instrument. The central parts M of the disc Pare preferably of wrought iron.
The pole piece S of the tubular part N, and polepiece N may be of a cast or
malleable cast iron. In Fig. 3 the pole pieces N & S are of wrought iron there
being a joint between N & the tubular part N. It is best to have all the iron
wrought iron. The cylindric polar surfaces N & S are not continuous; as shown
in Fig. 2 & described in my previous Patents 873 of 1890 & 7219 of 1890 these
surfaces are made discontinuous to produce a Foucault current resistance to motion
of the armature. The armature is a hollow cylinder of copper fastened as
shown to the spindle D & the worm F drives the counting wheels which record
the number of revolutions. The thickness of the copper cylinder is about half the
thickness of the space between the projections on N & S. L is a cover of wood or
vulcanized fibre. A is a ring of copper fastened to & fastening together S & N, a
leather washer being used so as to produce a mercury tight joint & mercury fills
the
space inside & outside C¹ up to the level K. The spindle and armature except
at its lower edge, are coated with insulating material. Current supplied to A passes
by the mercury to C & then to the spindle D.
C
A mercury cup revolving on the end of the spindle gives current through the
mercury to the fixed central conductor J which serves as a pivot & is adjustable &
current may be taken away by the metal frame H. The supports G & G¹are
shown insulated from H at their upper ends they may be made of iron or brass or
any strong material.
The lower pivot is shewn at V; the fixed parts of both
pivots may be of steel. The part of the pivot V which moves is sometimes
insulated from the rest of the armature, but I find this not very important as the
leakage is always small. I sometimes let current enter the mercury by a copper
ring, not underneath as shewn in the figure at A but at the upper part. The
present form works better.
In large instruments I sometimes insert a continuous ring of iron at the top or
bottom of S or of N or of both, so that at one part of the polar surfaces there shall
be less Foucault current effect than elsewhere & when this is the case, slightly
lowering or raising the armature alters the constant by a small amount, which may
be useful in adjustment. The raising and lowering of J by a metallic thermometer
may be made to produce this adjustment automatically to destroy effects due to
change of temperature.
An automatic diminution of the resistance of the branch containing the field
magnet winding will produce the same effect. The larger the instrument the
better it works.
If a specimen be made of the proportions shewn, the vertical height from P to H

page_text: being about one foot, the instrument will act well up to about 40 amperes. The
spindle D may be somewhat smaller just about K than elsewhere.
When I use no
gaps or discontinuities in the polar surfaces N or S I allow the spindle to drive an
auxiliary mass of copper in an auxiliary discontinuous field.
In the following claims, I shall use the term "two cup meter" to mean any
supply meter in which a conducting armature shaped like a surface of revolution
(disc, cylinder, cone &c.) receives & gives electricity by two bodies of mercury or
other conducting liquid.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what 1
claim is :-
"
1. In a two cup meter the immersion of the armature in one of the bodies of
mercury so that only a part of small diameter emerges from the surface of the
mercury.
2. In a "two cup meter," carrying the second cup or body of mercury on the
armature or spindle of the armature.
3. In a
66
two cup meter" coating the armature, except near the bounding edge
or at other definite places with an insulating coating so that a covering bath of
mercury acts really as if it were only a circular mercury trough.
4. The supply meter as described & shewn in Figures 1, 2 & 3.
Dated this 2nd day of November 1891.