Improvements in Electric Measuring Instruments.
Year: 1897

page_text: Date of Application, 28th Sept., 1897-Accepted; 20th Nov., 1897
COMPLETE SPECIFICATION.
Improvements in Electric 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.
of Swampscott, in the County of Essex, State of Massachusetts, United States of
America) 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 voltmeters and according to same a fixed coil is located
at a suitable angle, and a movable coil is placed within the fixed coil, at an angle
thereto; the movable coil being connected in series with the fixed coil and with
a resistance.
The construction is hereinafter fully set forth in reference to the accompanying
drawings in which
Fig. 1 is a transverse section through a voltmeter constructed in accordance
with this invenion, and
Fig. 2 is a plan thereof.
1 indicates the base of the instrument, of insulating material. To the base 1
is secured by screws 2, or other suitable means, the main frame 3 of the instru-
ment. In a suitable recess 4 in the main frame 3 is mounted a metallic frame 5
having the arms or brackets 6. Mounted in the frame 5 and in one of the
brackets 6 is a vertical rotary shaft 7 on which is mounted at an angle thereto
the movable coil 8. The movable coil is supported by a mica ring 9 secured to
Mounted at an angle
a bent strip 10 of aluminium fastened to the shaft 7.
and
enclosing the movable coil 8 is the fixed coil 11 secured by screws 12 to the
brackets 6. Mounted in a suitable recess 13 in the main frame 3 are resistance
spools 14 wound with a high resistance wire having a negligible temperature co-
efficient, such as manganene or German silver. The coils 8 and 11 are wound
with copper wire and the external resistance being of manganene, any substantial
heating effect is thereby removed from the coils 8 and 11. The coils 8 and 11
are connected in series with the resistance 14, and with each other. The ends of
the shaft 7 fare supported in adjustable bearings 16. Spiral springs 17 mounted
on the upper and lower ends of shaft 7 and connected to brackets 18 on frame 5
20 is the cap
and upper bracket 6, tend to bring the index 19, on shaft 7, to zero.
or cover for the upper end of shaft 7, secured to upper bracket 6 by screw 21. The
scale 22 is mounted on a support 23 secured to brackets 24 fastened to frame 5.
Beneath the support 23 is located the damper 25, consisting of a thin
aluminium sheet fastened to an aluminium wire '26, branching from the rear part
of the index 19, and secured thereto and to the shaft 7. The damper 25 may be
secured to the wire 26 in any suitable way, and as here shown by passing the
outer end of the wire in and out of slits or openings 27, in the sheet 26, and com-
pressing the parts together. 28 are the leads to the movable coil 8, flexibly con-
nected thereto and supported by a fibre insulation 29, as shown. 30, 30 are posts
connected to an outside circuit, the leads 28 being connected to said posts. 31 in-
.

page_text: dicates the switch. The connections to the circuit and through the coils and
resistance are clearly indicated by dotted lines.
Having now particularly described and ascertained the nature of the said in-
vention (as communicated to us from abroad) and in what manner the same is
to be performed, we declare that what we claim is :-
1
1. In an electric measuring instrument, a coil mounted at an angle on a shaft,
a second coil mounted at an angle to the first coil and its shaft and encircling the
same, the said coil being in series with the first coil, an indicator and scale for
reading the movements of the shaft and movable coil, and means for returning
the instrument to zero and opposing the movements of the movable coil under
the action of the current in said coils.
2. In an electrical measuring instrument, a coil mounted at an angle on a
shaft, a second coil mounted at an angle to the first coil and its shaft and en-
circling the same, the said coil being in series with the first coil, a high resist-
ance in series with said coils, an indicator and scale for reading the movements of
the shaft and movable coil, and means for returning the instrument to zero, and
opposing the movements of the movable coil under the action of the current in
said coils.
3. In an electrical measuring instrument, a coil mounted at an angle on a shaft,
a second coil mounted at an angle to the first coil and its shaft and encircling the
same, the said coil being in series with the first coil, a high resistance in series
with said coils, an indicator and scale for reading the movements of the shaft
and movable coil, a damper and means for returning the instrument to zero and
opposing the movements of the movable coil under the action of the current in
said coils.