Year: 1899

page_text: πιριον
We, JoN SEALY TOWNSEND, Gentleman, HAROLD ALBERT WILSON, Gentleman,
and JOHN ALEXANDER MCCLELLAND, Gentleman, all of Cavendish Laboratory, Cam-
bridge, in the County of Cambridge, do hereby declare the nature of this inven-
tion to be as follows:-
This invention relates to electrical measuring instruments, and has special
reference to electrostatic voltmeters.
Instruments of this description as hitherto made have the following disadvan-
tages: the deflection of the moving part is usually proportional to the square of
the voltage, and thus the scale is crowded at one part and too open at another;
the angular deflection of the moving part is limited to 90° or less; and the
constant of the instrument is fixed, or, at any rate, cannot be varied without
mechanical alteration of the moving part, say by the addition of weights to it.
In electrostatic voltmeters according to this invention these disadvantages are
obviated and the instruments produced can therefore be read with a greater mean
accuracy all over their scales, are capable of considerably greater angular deflee-
tions, and can be arranged so that by a simple alteration of the electrical con-
nections of the parts the constant of the instrument may be varied.
In carrying out this invention the parts which re-act when charged to produce
the deflection hereinafter called the attracting parts are so shaped that through-
out the greater part of the range of the instrument the angular deflection of the
movable part is approximately directly proportional to the difference of potential
between the attracting parts. Further, the formation of the attracting parts is
such that an angular deflection of considerably more than 90° can be obtained.
The improved voltmeters have some or all of the attracting parts-preferably
the cells or boxes into which the movable portion enters insulated from one
another, the separate parts being connected, singly or in sets, to any convenient
form of commutating or connecting device. By this means the number of active
portions may be varied, and thus any given angular deflection may represent two or
more definite voltages, that is to say, the instrument may have more than one
constant.
The following is a description, by way of example only, of one construction
of a multi-cellular electrostatic voltmeter according to this invention:-
The cells are made so that their shape in plan is approximately semi-circular,
and the moving portions or vanes are in the form of plates having one edge
approximately straight, while the other is curved in a cam-like fashion, the
particular shape of the curve determining to a large extent the law of the
instrument. The semi-circular cells are insulated from one another and are joined
in groups to the blocks of a commutating device, which is furnished with a
movable plate or equivalent, carrying contacts which alter the electrical con-
nections of the cells in a pre-arranged manner, and thus vary the constant of the
voltmeter. The insulated cells are preferably so. arranged that however they

page_text: may be grouped there is no twist or other force, except in the nature of a turning
moment upon the needle.
BOULT & WADE,
Agents for the Applicants.
Improvements in or relating to Electrical Measuring Instruments.
We, JOHN SEALY TOWNSEND, Gentleman, HAROLD ALBERT WILSON, Gentleman,
and JOHN ALEXANDER MCCLELLAND, Gentleman, all of Cavendish Laboratory, Cam-
bridge, in the County of Cambridge, 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:―
This invention relates to electrical measuring instruments, and has special
reference to electrostatic voltmeters.
In electrostatic voltmeters according to this invention some or all of the
attracting parts, that is the parts which re-act when charged to produce the deflec-
tion preferably the cells or boxes into which the movable portion enters-are
insulated from one another, the separated parts being connected, singly or in sets,
to any convenient form of commutating or connecting device. By this means the
number of active portions may be varied and thus any given angular deflection
may represent two or more definite voltages, that is to say the instrument may
have more than one constant.
Another feature of the improved voltmeters is that the vanes of the needles and
the cells or boxes into which those vanes enter are so sliaped and arranged that
a large deflection is obtained. Further the formation of the vanes and cells is
such that throughout the greater part of the range of the instrument the angular
deflection of the movable part is approximately directly proportional to the
difference of potential between the attracting parts.
The following is a description, by way of example only, of one construction
of a multi-cellular electrostatic voltmeter according to this invention:
The cells are made so that their shape in plan is approximately semi-circular
and the moving portions or vanes are in the form of plates having one edge
approximately straight, while the other is curved in a cam-like fashion, the
particular shape of the curve determining to a large extent the law of the
instrument. The semi-circular cells are insulated from one another and are joined
in groups to the blocks of a commutating device, which is furnished with a
movable plate or equivalent, carrying contacts which alter the electrical con-
nections of the cells in a pre-arranged manner, and thus vary the constant of the
voltmeter. The insulated cells are preferably so arranged that however they
may be grouped there is no twist or other force, except in the nature of a turning
moment upon the needle.
In the accompanying drawings, which illustrate diagrammatically various
portions of one construction of multi-cellular electrostatic voltmeter according to
this invention,
Figure 1 is a plan showing the shape and relative position of the attracting
.parts.
Figure 2 is a central vertical section on the line 2-2 of Figure 1, showing also
.the electrical connections of the cells.
Figure 3 is a plan showing the disposition of the vanes upon the spindle.
Figure 4 is a sectional elevation of the commutating device, and
Figures 5 and 6 are plans of a portion of the same showing it in two positions.
Like letters indicate like parts throughout the drawings.

page_text: With reference first to Figures 1 and 2 A is a central spindle pivotted or
suspended in any convenient way and carrying upon it a number of shaped flat
vanes A A A A+ A A A A8. "The cells into which the vanes move are of semi-
circular shape in plan and are formed of a number of metallic plates B mounted
upon insulating rods C which pass through holes C in the plates B. Each plate B
has a small area cut away at its centre through which the spindle A passes.
The
plates Bare kept apart at fixed distances by washers or distance pieces D and D.
The washers are of metal and serve to connect the plates B on either side of
them. These washers are, for the sake of clearness, shaded in Figure 2.
The
washers Dunshaded in Figure 2-are of insulating material say ebonite and
thus serve to insulate from each other the plates on either side of them.
The cells or boxes, that is the spaces between the plates B, are for convenience
of reference numbered B1 to B316. The cells 39 B10 B3 B4 B 336 B5 B16 are con-
nected together and to the base E of the instrument. The cells B B B 13 BB
and 138 are in metallic connection with a spring F forming part of a commutating
device hereinafter described. These cells are insulated from the rest of the
apparatus. The cells B and B are also insulated from the rest of the apparatus
and are in metallic connection with a second spring F
Each of the vanes A A-A8 is shaped as shown in Figure 1, this shape being
calculated so that when the vane is used as shown, in conjunction with fat semi-
circular cells the deflection is approximately proportional to the difference of
potential between the attracting parts. If it is desired that the instrument shall
have a straight line law" after the deflection reaches any given point, this
may be brought about by slightly altering the shape of the vanes. The cells B¹
B2B16 are made of semicircular shape in plan in order that a large angular
displacement of the needle may be obtained.
Figure 1 shows. one vane A¹ only, its position relatively to the cells being the
position of no deflection. In the figure the edges of two cells B B are repre-
sented by dotted lines, the cell B would be made of the same potential as the
vane A The small arrow shows the direction in which the vane would be
attracted into the cell B¹.
The shaped vanes A¹ AAs are arranged symmetrically upon the spindle A,
that is four of them, vir: A A A A are arranged at 180° to the other four, ris:
A A A Aº.
The commutating device F, Figures 4, 5, and 6, comprises a disc 13 of insulating
material say ebonite, having two arc-shaped contact plates F and secured to
its periphery. The contact plate is connected by a metal strap F to a bottom
pivot 17 which works in a support 18 which is in electrical connection with the
base of the instrument. The contact plate 15 is connected by a
metal strap F to a spindle 10 central with the disc and capable
of rotation within a metal tube which is fixed in an insulating plate F
The tube F is connected as by a wire F to a terminal G. A milled head F1 of
insulating material is secured to the top of the spindle F10 so that the disc F
may be rotated.
When it is desired to measure the difference of potential between two conductors,
one of them is joined by any convenient means to the base E of the instrument and
the other to the terminal G.
As herein before described certain of the insulated cells are joined to contact
springs FF. These contact springs are shown diagrammatically in Figures 5
and in the positions which they occupy with regard to tlie disc E and the
contact plates 1 F upon it. It will be seen that in Figure 5 both the springs F
and are in contact with the contact plate F, that is they are both in connection
with the terminal G. In this position therefore eight cells rir: B B B B B
BBB are joined to the base and the remaining eight cells ris: B B Bu
B13 B13 B B B are connected to the terminal G, all the cells being thus used
to measure a difference of potential between the base. E and the terminal G.
Suppose now the commutator F to be turned into the position indicated in Figure 6

page_text: the spring F now makes contact with the plate F that is to say
it is connected through the support F8 to the base E, and the spring a
is connected through the plate to the terminal G. In this position the
cells B B B B12 B1 and B8 which are permanently connected to the spring Fl
will be at the same potential as the cells. B B10 B3 B B and 1316 so that the six
vanes A A A A A³ and As will not be acted upon by an electric force. The
cells B and B connected through the spring F to the terminal G attract the
vanes A and A', so that in the position indicated in Figure 6, only two vanes
exert a force which tends to turn the spindle.
The deflection produced by a difference of potential when the commutator is in
the position shown in Figure 5 is equal to the deflection produced by twice that
potential difference when the commutator is in the position shown in Figure 6.
The particular instrument described above is merely by way of example in
order to illustrate one method of varying the constant of an electrostatic voltmeter
by altering the electrical connections of its cells. Various modifications may be
made without departing from the spirit of this invention, for example different
sized vanes may be carried on the same spindle, the commutator being arranged
so as to bring into action the cells into which either the large or the small vanes
are attracted. Again the cells in the one instrument may be made of various
widths the commutator determining which cells are brought into action.
The number of constants for one instrument is not limited to two; obviously
the cells may be joined up so that the commutator may have three or more effective
positions. It is however found in practice that it is preferable not to have more
than three constants for the one instrument.
Having now particularly described and ascertained the nature of our said
invention, and in what manner the same is to be performed, we declare that what
we claim is:-
1. An electrostatic voltmeter in which one or both of the parts which re-act
to produce the deflection is divided into separate portions insulated from one
another so that their electrical connections may be varied.
2. A multi-cellular electrostatic voltmeter having the cells or boxes in which
the movable portion operates insulated from one another.
3. In a multi-cellular electrostatic voltmeter the combination with a spindle
of a series of shaped vanes such as A¹ substantially as described.
4. In a multi-cellular electrostatic voltmeter the combination with cells or
boxes insulated from one another and connected to a commutating device of a
spindle carrying a series of shaped vanes.
5. An electrostatic voltmeter having flat cells so arranged that the flat vanes
which operate in the cells are capable of deflection through more than 90°.
6. In a multi-cellular electrostatic voltmeter the combination and arrangement
of vanes and cells substantially as described and illustrated in Figures 1, 2 and 3
of the accompanying drawings.
Dated this 30th day of December 1899
BOULT, WADE & KILBURN,
Agents for the Applicants.