Year: 1885

page_text: We, OTWAY EDWARD WOODHOUSE, and FREDERICK LAWRENCE RAWSON, both
of No. 11 Queen Victoria Street, in the City of London, and JOHN HUBERT
DAVIES, of 73 Talgarth Road, in the County of Middlesex, and EUGENE JOSEPH
MOYNIHAN, of 31 Weltje Road, Hammersmith, in the County of Middlesex, all
Electrical Engineers, do hereby declare the nature of this invention to be as
follows:-
Our invention relates to improvements in Wheatstone bridges in which the
ratio arms are formed by a stretched wire and their ratio is altered by shifting
the point of contact of the battery lead; which arrangement is commonly called a
metre bridge.
We wind the wire, which forms the ratio arms, called herein the metre wire, in
one groove of a double threaded screw cut on a cylinder of ivory or other suitable
insulating material, in the other groove of which is wound a wire connected to one
pole of a battery and called the battery wire. The ends of the metre and battery
wires are connected in the ordinary way.
Connection is made between the metre
and battery wires by a forked spring, rubbing on both wires, and fixed to a ring
screwing up and down on the cylinder. In some cases we use this arrangement in
combination with an ordinary Wheatstone's plug bridge, in which case the infinity
plug hole is placed between the adjustable arm of the plug bridge and the block to
which the known resistances in the metre bridge can be connected. The infinity
plug hole and the plug-holes in the metre bridge have only one plug, fitting them
all, and differ in size from those in the plug bridge so that when the Wheatstone's
plug bridge is used, the known resistances of the metre bridge must be unconnected
and when the metre bridge is used the infinity plug-hole of the Wheatstone's plug
bridge must be unplugged. We make the connections so that the same terminals
serve for both bridges. To economise space, we use for the galvanometer and
battery circuits contact keys which consist of a metallic rod, sliding, and free to
turn, in a metallic sleeve. This rod is furnished at the top with a head larger than
the bush and slides through a hole in a lever which projects beyond the head and
is pressed down on to the top of the bush by a spiral spring placed between the
head and lever, and surrounding the sliding rod. The levers of both contact keys
are connected by an insulated connecting rod. In the head of the sliding rod
is fixed a contact pin, which passes through a hole in the lever clear of the bush.
מ

page_text: This pin, when the head is depressed, makes contact with either of two contact
studs one being connected to the metre, and the other to the Wheatstone's plug
bridge, the insulated connecting rod insuring that both are in a position to make
contact with either the plug or the metre bridge studs. In some cases we place a
galvanometer or battery, or both, and the known resistance coils of the, metre
bridge within the threaded cylinder and the metal connecting blocks on the top of
the cylinder.
When we want to make connection between a heavy cable and the ordinary
terminals, we employ a piece of flat copper strip with a slot in one end, which
passes under the clamping nut of the ordinary terminal of the bridge. The other
end has fixed to it a Woodhouse & Rawson's split terminal which easily receives
the cable.
200K
FELL & WILDING,
Agents for the Applicants.
COMPLETE SPECIFICATION.
Improvements in Apparatus for Measuring Electric Resistances.
יד. . .
We, OTWAY EDWARD WOODHOUSE and FREDERICK LAWRENCE RAWSON, both.
of No. 11 Queen Victoria Street, in the City of London, and JOHN HUBERT
DAVIES, of 73 Talgarth Road, in the County of Middlesex, and EUGENE JOSEPH 2
MOYNIHAN, of 31 Weltje Road, Hammersmith, in the County of Middlesex, all
Electrical Engineers, do hereby declare the nature of this invention and in what
manner the same is to be performed to be particularly described and ascertained
in and by the following statement:-
Our invention relates to improvements in Wheatstone bridges in which the
ratio arms are formed by a stretched wire and this ratio is altered by shifting
the point of contact of the wire, which makes connection, to one of the terminals of
the battery or galvanometer, which arrangement is commonly called a metre-
bridge. We wind the wire which forms the ratio arms of the bridge called herein
the metre wire, which may however be of any convenient length, in one groove of
a double threaded screw, cut on a cylinder of ivory or other suitable insulating
material mounted on or forming one with an insulating base and another wire
which is connected to one terminal of the battery or galvanometer preferably the
former, and called herein the battery wire" in the other groove of the said screw.
Connection is made between the two wires by a 'metallic spring rubbing on both
wires or carrying metallic rollers which run on both wires or rubbing on one wire
and carrying a metallic roller running on the other. This spring is fastened to a
ring-put in any Buitable way which screws up
screws up and down the insulating cylinder
"
"
:

page_text: and has graduations on it, showing parts of a turn or half turn, the number of
turns or half turns being shown by a vertical scale close to the ring. The ends of
the metre wire pass over projections or metallic contact pieces let into the screw
thread and are fastened to them in any suitable manner preferably by tacking with
solder and a screw entering the metallic piece. These two metallic pieces are con-
nected to terminals in the ordinary way. The resistance coils with which we
supply our metre bridge may be four in number and we permanently connect them
up between the metal block at one end of the "metre wire" and separate plug
blocks which can be individually connected to a terminal block, the resistance coil
BO connected forming the third or adjustable arm of the bridge as will be well
understood. One end or in some cases both ends of the battery wire or the screwed
cylinder are fastened to a rod or other suitable piece of metal which is connected
preferably through a contact key to a terminal on the insulating base. There may
be any number of complete turns or half turns of the metre wire on the insulating
threaded cylinder preferably ten. In measuring resistance a battery and galvano-
meter are connected in the ordinary way and one of the resistance coils in the
adjustable arm plugged; the ring-nut carrying the contact spring is then screwed
up or down until no deflection is obtained on the galvanometer. The ratio of the
two arms of the bridge formed by the metre wire is then found by reading.the
graduations on the ring and vertical scale and the resistance calculated by a well
known formula. In some cases we use this metre bridge in combination with an
ordinary Wheatstone plug bridge and we then place the infinity plug hole of the
plug bridge between the metallic block to which any of the four known resistances
of the metre bridge may be connected, and the end block in the adjustable
resistance arm of the plug bridge. There is only one plug fitting the infinity plug
hole and the four holes in the metre bridge blocks, these holes being of a size
different from those in the plug bridge to ensure that when one bridge is in use,
the other must be necessarily disconnected. We make the connections in this
combination so that the same terminals serve for both bridges, thus uniting
them in one instrument. When the metre bridge is in use, the plug herein-
above mentioned is used to connect one of the four known resistances and the
infinity plug hole is consequently unplugged. When the plug bridge is in
use, this plug must be in the infinity plug hole. To economise space, we use a
special form of contact key. When used with our metre bridge, it consists of a
metallic rod sliding vertically, but not free to turn, in a sleeve fixed in the
threaded cylinder, and normally held up by a spiral spring placed suitably,
preferably between the top of the sleeve and the head fixed to the sliding rod.
This head is larger than the sleeve and carries near its edge a metallic pin, pro-
jecting downwards. When the head is depressed against the force of the spring,
this pin makes contact with a contact stud fixed in the insulating cylinder and
forming one terminal of the contact key, the sleeve forming the other terminal.
When used with our combination plug and metre bridge, the sliding rods in the
contact keys are capable of rotation, as well as vertical motion, and the pins in
their heads slide through holes in levers turning about the sliding rods, and held
down by the spiral springs above mentioned. The extremities of these levers are
joined by a connecting rod of insulating material, and their angular motion is
limited by two stops. When the levers are moved to the right, and the contact
keys depressed, the circuits completed are those belonging to one bridge; and
when they are turned to the left, to the other bridge. By means of a spring they
are prevented in a way which will be understood from the drawings from being
left in an intermediate position. In some cases in making our metre bridge, we
place a galvanometer, or battery, or both, within, and the terminals and contact
keys or connecting blocks or both on top of the insulated threaded cylinder.
When it is desired to measure the resistance of heavy cable, we clamp it in
large terminals which are fixed on one end of pieces of stout copper strip, the other
ends having slots cut in them, enabling them to be clamped underneath the ordinary
terminal nuts of the bridge.

page_text: In order that our invention may be the better understood, we now proceed to
describe the same in relation to the drawings hereunto annexed. The numerals
and capital letters on the drawings are those which are actually engraved on the
instruments, and the small letters which indicate smaller parts in the different
figures are the reference letters for this specification.
Figure 1 is a general plan of our combined metre bridge and Wheatstone plug
bridge.
Fig. 2 is a detailed plan of the movable contact keys j and j¹.
Figure 3 is a vertical section through one of them.
Figure 4 is a detailed elevation of our metre bridge (as in Figure 1) in a compact
form for use without a plug bridge.
Figure 5 is a plan of the same.
In figure 1 a is the insulated threaded cylinder (seen more clearly in detail in
figure 4) b is the ring which screws up and down, carrying within it the contact
spring c, which presses on the battery wire and the roller d, which runs on the
metre wire. The ring is graduated on the outside to show the parts or half turns
made, and the vertical scale x shows the number of half turns; f is the projection
⚫ on the piece of metal, i, let into the cylinder over which one end of the metre wire
passes, being fastened beneath a screw which enters the said metallic piece. The
other end is fastened similarly to another piece of metal underneath the cylinder,
into which screws the metallic rod g shown by a dotted circle. The battery wire
is connected to the rod h; j and j¹ are the battery and galvanometer contact
keys, m n and m n¹ are metallic studs fixed in the ebonite slab o, on which all
the work of the bridge is planted; t¹¹ are the blocks, of the plug bridge to
which the proportioned coils are connected; t t. are those to which the coils of
the adjustable arm are connected; u and u u¹ are the blocks connecting the
known coils of the metre bridge; w₁ w₁ w, w₁ are terminals. The connections
shewn by the dotted lines are as follows; from w, to g, h to n¹, j¹ to wμ i through
the resistance coils r r to u u, i to n, j to w,, m¹ to l, m to k.
In figures 2 and 3 7 7¹ are the sliding rods 55 the metallic sleeves in which
they slide and turn w, a pin limiting the upward motion
levers turning
about 1x, the insulating rod connecting & the spiral spring which holds up the
sliding rod, e a metallic connection between ' and the contact pins xx¹¹.
and contact studs fastened in the ebonite plate o, p is a spring in tension
between K and S which is a pin fixed in the ebonite T T¹ are stops limiting the
motion of T¹.
In figures 4 and 5, a is the double threaded insulating cylinder 6 the ring
screwing thereon carrying in a slot within it the spring c which makes contact
with the battery wire and carries the roller d running on the metre wire f and g
the metallic pieces to which the metre wire is fastened and a the vertical scale.
The battery wire is carried through the small hole h and connected within the
cylinder through the battery contact to the battery terminal.
Figure 6 is a plan and figure 7 an elevation of the terminal for attaching heavy
cable previously described.
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 :—
1st. The combination of a double threaded cylinder of insulating material
carrying in its two parallel threads the resistance or 'metre' wire, forming the
ratio arms of a metre bridge and the battery wire respectively, with a ring-nut
carrying any suitable metallic contact, and provided with a graduated scale on the
ring-nut and external vertical scale, to measure the angular movements of the said
ring-nut, and constituing a so-called metre-bridge to test electric resistances,
substantially as described.
2nd. The combination in such a metre-bridge of such a double threaded cylinder
and ring-nut carrying contacts with switch keys, plug blocks and resistance coils,

page_text: a battery and galvanometer, or with one or more of them, in one instrument, as
and for the purposes, substantially as described.
3rd. The combination of a resistance metre bridge as claimed in claim 1 with a
Wheatstone plug-bridge and alternative switch keys in one instrument the infinity
plug hole and metre bridge resistance plug hole being provided with only a single
plug, and of a different size to the other plug holes of the Wheatstone plug bridge,
as and for the purposes substantially as described.
4th. The construction of the switch keys, consisting of a spring push with a
contact pin under the push-head capable also of angular movement if required,
making contact with one or more insulated rods or bars under the push-head,
substantially as described.
5th. The combination of two or more such switch keys as claimed in claim 4
and constructed so as to be capable of angular movement on their axis, with a
connecting link and spring attached thereto, causing such two or more linked
switch keys to move angularly simultaneously, and preventing them from resting
without completion of the angular movement substantially as described.
Dated.cals 10th day of September 1885.
FELL & WILDING,
1, Queen Victoria Street, London, E.C.,
Agents for the Applicants.