Improvements in Electro-static Measuring Instruments,
Year: 1898

page_text: Date of Application, 20th Sept., 1898-Accepted, 12th Nov., 1898
COMPLETE SPECIFICATION.
Improvements in Electro-static Measuring Instruments,
We, THE BRITISH THOMSON-HOUSTON COMPANY, LIMITED, of 83, Cannon Street,
in the City of London, Electrical Engineers, do hereby declare the nature of this
invention (which has been communicated to us from abroad by Elihu Thomson,
residing at Swampscott, County of Essex, State of Massachusetts, United States of
America, Electrician) and in what manner the same is to be performed. to be
particularly described and ascertained in and by the following statement:-
The present invention relates to electro-static measuring instruments designed
to measure high potentials; it relates more particularly to instruments employed
on alternating current circuits, and is adapted to indicate as high voltages as
20,000 volts, for example.
The invention has for its object to provide a shield for the operating parts of the
instrument, which is located between said operating parts and the surrounding case,
thereby preventing the static condition of the case from affecting the indications
of the instrument.
The invention provides certain damping devices for use in an electro-static
indicating instrument.
The invention also relates to certain novel features in the construction, to be
more fully described and claimed hereinafter.
In the accompanying drawings attached to and made a part of this specification,
Fig. 1 is a sectional view of an instrument made in accordance with the present
invention, Fig. 2 is a plan view of the instrument with the surrounding casing
removed, Fig. 3 is an isometrical view with the casing removed, and Fig. 4 is a
modification of one of the vanes.
The base B sustains the several parts of the instrument, and is provided with
lugs B¹ for securing it to a support. Mounted upon the base is a circular
auxiliary base R of insulating material, having a shoulder near its outer periphery
forming a support for the circular metal shield G. The shield may be con-
structed of perforated metal or wire gauze, or of any conducting material, the
structure of which virtually surrounds the working parts of the instrument.
Extending across the top of the shield is a metal piece A in which is mounted a
jewel P forming the upper bearing of the shaft X, and in the insulating base
is mounted a jewel P¹ forming the lower bearing.
Mounted on the insulating base R and concentric with the shaft X is a stationary
electro-static inductor H having an upwardly extending part or quadrant h
mounted in a support Q, and a downwardly extending part or quadrant h¹, mounted
in a groove in the base, the two being connected by strips 3. Situated within
the inductor H and concentric therewith is a second electro-static inductor F
having an upwardly extending part or quadrant f and a downwardly extending
part or quadrant fi, the two parts being connected by strips f. Both inductors
are supported in a similar manner, and corresponding parts are placed opposite.
Price 8d b

page_text: The inductors F and H are electrically connected and a wire extends therefrom
to binding post M; this wire is sustained in air, and is sufficiently insulated from
all parts of the instrument to stand the maximum voltage without leakage.
and vane
Mounted on the shaft X for oscillating movement between the stationary
inductors are thin sheets or vanes of aluminum E, E¹ made in the form of a
segment of a cylinder; vane E working between the upwardly extending parts h, f
E between the downwardly extending parts h, f, of the inductors.
These vanes or sheets may if desired be perforated as shown in Fig. 4, to reduce
the weight, without materially decreasing the electro-static effect between the
vanes and the surrounding electro-static inductors. The space between the vanes E
and E and the outer and inner inductors F and H is made sufficient to insulate for
the potential at which the instrument is to be used.
Secured to the insulating base is a frame Y surrounding the shaft and support-
ing the outer ends of the spiral springs V, the inner ends of which are attached
to the shaft; the tension of the spring is arranged to turn the needle I to zero
when no deflecting force exists. Connecting the binding posts N and the frame Y
is a wire b which through the shaft and springs, connects the vanes E and E' with
the binding post. The shield G is also in electrical connection with the binding
post N.
A series of magnets L, L, preferably permanent, is arranged at intervals with
their free pole extending upward, so that the vane E in moving will cut the line
of force. This induces current in the vane and prevents two violent oscillations
of the needle when actuated by the electro-static field or by the springs. The
magnets L, L need not be insulated from the conductors F and M, but can be
carried or guided by them; or the magnets may serve in part to support the
inductors. A vibrating needle I is mounted on the shaft X and extends through
a slot Z in the shield G and works over a scale plate S which is supported by
insulating brackets D. When the vanes E, E, the needle I and the shield G are
electrified, the scale becomes of the same polarity.
Surrounding the instrument is a case C provided with a window W closed by
glass or other transparent substance. The window is preferably covered on one
or both sides with a fine wire netting electrically connected to the case C and
having an open mesh so as not to obstruct the view of the needle and scale. The
netting may be made in a variety of ways, for example it may be made of fine
wire or of thin strips of semi-conducting material, more or less perforated. This
netting or conducting mesh-work prevents any electrification of the glass, due
to any local action, having any effect upon the needle, by distributing any electro-
static charges or inductively binding them so that they have no value.
The operation of the instrument is as follows: the stationary inductors H and F
being connected to one side of the high potential system through binding post M
and wire, and the moving vanes E, E and shields G being connected by wire b
to the binding post N and opposite side of the system, the electro-static condition
of the circuit at any instant is communicated to the moving vanes and inductors,
and as the vanes at the start are displaced relatively to the stationary inductors,
the electrification of one or both of them causes a tendency of the vanes to move
to a position where their surfaces are directly and completely opposite to the
inductors; this tendency being opposed by spiral springs V. During the move-
ment of the vane E it passes through the magnetic fields of the damping magnets L
and eddy currents are set up in the same which tend to check its two violent
motion. The enclosing cylindrical shield G cuts off all extraneous inductive actions
which might be exerted between the moving vanes and the surrounding case to
an extent to produce errors in the readings. The shield G constitutes an electro-
static diaphragm, and its connection to the binding post to which the moving
vanes are connected ensures its always having a definite electrical relation to the
For example, if by accident the surrounding case should be in leakage
connection with either terminal or should become electrified to a greater or less
extent, it might without the shield act to deflect the needle from its proper reading.
vanes.

page_text: Having now particularly described and ascertained the nature of our said inven-
tion (as communicated to us from abroad) and in what manner the same is to be
performed, we declare that what we claim is:-
1-In a static measuring and indicating instrument, the combination of station-
ary inductors and a vibrating needle the vanes of the needle being segments of a
cylinder, with a permanent magnet whose lines of force cross the path of one of
the vanes of the needle at substantially at right angles thereto.
2 In a static measuring and indicating instrument, the combination of fixed
inductors and a vibrating needle having vanes in close proximity to said inductors,
with an insulating dielectric between said vanes an inductors, and a permanent
magnet whose lines of force across the path of one of the vanes of the vibrating
needle.
3-In a static measuring and indicating instrument, the combination of a vibrat-
ing needle having vanes and fixed inductors in close proximity to said vanes, the
vanes and inductors being cylindrical in form, with an insulating dielectric between
the vanes of said needle and said inductors, and permanent magnets so arranged
that their arms are upon opposite sides of the path of one of the vanes.
4-In a static indicating instrument, the combination of outer and inner station-
ary inductors having upper and lower quadrants, as described, with a needle having
vanes circular in outline, which move in the spaces between the different quadrants
of the inductor, as described.
5 In a measuring and indicating instrument, the combination of a vibrating
needle and stationary inductors separated from each other by an insulating
medium, with a shield enclosing the moving parts of the instrument.
6 In a measuring and indicating instrument, the combination of a vibrating
needle and stationary inductors separated from each other by an air space, and a
metal shield enclosing the moving parts of the instrument to protect them from
extraneous inductive actions.
7-In a static measuring and indicating instrument, the combination of fixed
and movable bodies in inductive relation to each other, a case surrounding the
instrument, and a shield mounted between the surrounding case and the working
parts of the instrument, connected to one side of the system with which the instru-
ment is in circuit.
8-In a static measuring and indicating instrument, the combination of a
vibrating needle vanes for moving the needle stationary inductors separated from
each other by an insulating medium, and a cylindrical metal shield surrounding
the operating parts of the instrument to prevent extraneous inductive actions
from affecting the readings.
9-In a static measuring and indicating instrument, the combination of a
vibrating needle and stationary inductors separated from each other by an insulat-
ing medium, a scale over which the needle moves, a case surrounding the instru-
inent having a glass covered opening and means preventing any electrification of
the glass from affecting the indication of the instrument.
10 In a static measuring and indicating instrument, the combination of a
vibrating needle, and stationary inductors separated from each other by an insulat-
ing medium, a scale over which the needle moves, a case surrounding the instru-
ment, having a glass covered opening, and a metal screen covering the glass pre-
venting any local electrification from affecting the indications of the instrument.
11 In a static measuring and indicating instrument, the combination of a
vibrating needle, vanes for moving the needle, stationary inductors acting upon
the vanes, a scale plate over which the needle moves, a case surrounding the
instrument having a glass covered opening, and a wire screen electrically con-
nected to the case located over the needle.
12. In a static measuring and indicating instrument, the combination of a
stationary inductor mounted concentric with the shaft of the instrument, and
having upwardly and downwardly extending quadrants, a secondary conductor

page_text: similarly shaped mounted within the first, and vanes mounted on the shaft in such
manner that one of them is affected by the upwardly extending quadrant and the
other by the downwardly extending quadrant of both of the inductors.
Dated this 20th day of September 1898.
THE BRITISH THOMSON-HOUSTON CO., LTD,
A. R. MONKS,
Director.
ALFRED CLEMENTS,
Assistant Secretary.