Improvements in Electrical Measuring Instruments.
Year: 1899

page_text: Date of Application (in United Kingdom), 31st Oct., 1899
Complete Specification Left, 30th July, 1900-Accepted, 15th Sept., 1900
Improvements in Electrical Measuring Instruments.
We, HARRY PHILLIPS DAVIS, of 327, Neville Street, Pittsburg, and FRANK
CONRAD, of 709, Whitney Avenue, Wilkinsburg, both in the County of Allegheny
and State of Pennsylvania, United States of America, Electrical Engineers, do
hereby declare the nature of this invention to be as follows:
--
Our invention relates to electrical measuring instruments which are adapted
for measuring direct currents, and comprises an improved instrument of the
type in which the current to be measured passes through a coil which can move
in a magnetic field, its movement being opposed, however, by a restraining
device such as a spiral spring for example.
The improved instrument is illustrated in the accompanying drawing, in
which
Figure 1 is a front elevation, portions being broken away and
Figures 2 and 3 are detail views of the movable members of the instrument.
Figure 4 is a section on the line IV-IV, Figure 1, and
Figure 5 an under plan view partly sectional.
1 is the field magnet which is composed of two permanent magnets 2 and 3,
poles of like polarity being placed opposite each other. Clamped between one
pair of poles of the same polarity is a polar extension 4, the projecting portion
of which extends toward the opposite magnet pole through approximately a semi-
circumference. 5 is a similar extension secured between the other pair of magnet
poles in a plane parallel to the extension 4, from which it is separated by an
air gap 6.
7 is the scale plate supported by brackets 8 and 9, to which is also
secured a rectangular frame 10 which supports the bearing pins 11 and 12. The
movable coil of the instrument is wound upon a bobbin 13, preferably stamped
from sheet aluminium, to which is attached a damper plate 131 and arms 14 and 15
(see Figures 2 and 3) the arm 14 carries a pointer 16 and is furnished with a
hook 141 in which is clamped the insulated outer end of a spiral spring 17, the
inner end of which is secured to the bearing pin 11. The arm 14 also carries a
steel point 19 which has its bearing in a jewel set in the end of the pin 11. The
arm 15 carries a steel point 20 which has its bearings in a jewel set in the end of
pin 12, said arm is also furnished with a hook 211, to which the insulated outer
end of a second spiral spring 22 is clamped, the inner end of the spring being
fastened to the pin 12. The coil 24 which is wound upon the bobbin 13 has its
terminals connected to the outer ends of the springs 17 and 22, and the pins 11
and 12 are connected by wires 27 and 28 to the binding posts 25 and 26 of the
instrument. A current adjusting resistance 31 is included in the conductor 27.

page_text: 32 is a shield made of magnetic material in order to equalise the magnetic field
of the instrument, said shield is constituted by a segment of a hollow cylinder
and is adjustably secured to a stationary part of the instrument.
By forming the bobbin 13 of a single sheet of metal and so fastening the
damper plate 131 thereto as to make the two substantially a single element
electrically, we provide a very desirable damping device which is effective in
operation and at the same time so light and well balanced that there is a minimum
amount of weight on the bearings and consequently a minimum degree of
frictional resistance to the movement of the operating and indicating mechanism.
The shape of the damper plate is made such as to substantially balance the
moving parts upon the bearings, and such as to give the required damping effect
during the entire range of movement of the indicating pointer.
By attaching the inner ends of the spiral springs 17 and 22 to stationary
portions of the instrument, substantially all of the weight of the springs is taken
off the moving members of the instrument, and the bearings are thereby relieved
of the friction due to the weight of the springs as ordinarily supported in this
class of instruments.
We have shewn the field magnet as being composed of two portions; it will be
understood, however, that this magnet can be constituted by a single piece if
desired.
It will be obvious that the instrument above described may be used as a volt
meter as well as an ampere meter, as is the case with all instruments of this
general type.
W. P. THOMPSON & Co.,
322, High Holborn, London, W.C., Patent Agents for the Applicant.
.
Improvements in Electrical Measuring Instruments.
We, HARRY PHILLIPS DAVIS, of 327, Neville Street, Pittsburg, and FRANK
CONRAD, of 709, Whitney Avenue, Wilkinsburg, both in the County of Allegheny
and State of Pennsylvania, United States of America, Electrical Engineers, do
hereby declare the nature of this invention, to be particularly described and
ascertained in and by the following statement:-
Our invention relates to electrical measuring instruments. which are adapted
for measuring direct currents, and comprises an improved instrument of the
type in which the current to be measured passes through a coil which can move
in a magnetic field, its movement being opposed, however, by a restraining
device such as a spiral spring for example. The improved instrument is illus-
trated in the drawing filed with our Provisional Specification in which
Figure 1 is a front elevation, portions being broken away and
Figures 2 and 3 are detail views of the movable members of the instrument.
Figure 4 is a section on the line IV-IV. Figure 1, and
Figure 5 an under plan view partly sectional.
1 is the field magnet which is composed of two permanent magnets 2 and 3,
poles of like polarity being placed opposite each other. Clamped between one
pair of poles of the same polarity is a polar extension 4, the projecting portion
of which extends toward the opposite magnet pole through approximately a semi-
circumference. 5 is a similar extension secured between the other pair of magnet
poles in a plane parallel to the extension 4, from which it is separated by an
air gap 6.
7 is the scale plate supported by brackets 8 and 9, to which is also
secured a rectangular frame 10 which supports the bearing pins 11 and 12. The
movable coil of the instrument is wound upon a bobbin 13, preferably stamped

page_text: from sheet aluminium, to which is attached a damper plate 131 and arms 14 and 15
(see Figures 2 and 3) the arm 14 carries a pointer 16 and is furnished with a
hook 141 in which is clamped the insulated outer end of a spiral spring 17, the
inner end of which is secured to the bearing pin 11. The arm 14 also carries a
steel point 19 which has its bearing in a jewel set in the end of the pin 11. The
arm 15 carries a steel point. 20 which has its bearing in a jewel set in the end of
pin 12, said arm is also furnished with a hook 211, to which the insulated outer
end of a second spiral spring 22 is clamped, the inner end of the spring being
fastened to the pin 12. The coil 24 which is wound upon the bobbin 13 has its
terminals connected to the outer ends of the springs 17 and 22, and the pins 11
and 12 are connected by wires 27 and 28 to the binding posts 25 and 26 of the
instrument. A current adjusting resistance 31 is included in the conductor 27.
32 is a shield made of magnetic material in order to equalise the magnetic field
of the instrument, said shield is constituted by a segment of a hollow cylinder
and is adjustably secured to a stationary part of the instrument.
By forming the bobbin 13 of a single sheet of metal and so fastening the
damper plate 131 thereto as to make the two substantially a single element
electrically, we provide a very desirable damping device which is effective in
operation and at the same time so light and well balanced that there is a minimum
amount of weight on the bearings and consequently a minimum degree of
frictional resistance to the movement of the operating and indicating mechanism.
The shape of the damper plate is made such as to substantially balance the
moving parts upon the bearings, and such as to give the required damping effect
during the entire range of movement of the indicating pointer.
By attaching the inner ends of the spiral springs 17 and 22 to stationary
portions of the instrument, substantially all of the weight of the springs is taken
off the moving members of the instrument, and the bearings are thereby relieved
of the friction due to the weight of the springs as ordinarily supported in this
class of instruments.
We have shewn the field magnet as being composed of two portions; it will be
understood, however, that this magnet can be constituted by a single piece if
desired.
It will be obvious that the instrument above described may be used as a volt
meter as well as an ampere meter, as is the case with all instruments of this
general type.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed, we declare that what we
claim is:-
1. In an electrical measuring instrument of the kind described, a bobbin
combined with a damper plate, said damper plate being located between the
polar extensions of the magnet and the bobbin surrounding one of said extensions,
substantially as described.
2. The combination with a movable actuating coil of an electrical measuring
instrument, of a spiral spring tending to hold the coil in its initial position, the
weight of said spring being supported by a stationary part of the instrument
substantially as described.
3. An electrical measuring instrument constructed substantially as described
with reference to the accompanying drawings.
Dated this 30th day July 1900.
FREDERICK WILLIAM LE TALL,
Chartered Patent Agent,
The Westinghouse Patent Bureau,
Westinghouse Building, Norfolk St., Strand, London, W.C.,