IMPROVEMENTS IN THE CONSTRUCTION OF APPARATUS FOR EFFECTING ELECTRICAL MEASUREMENTS."
Year: 1881

page_text: LETTERS PATENT to John Clement Cuff, of Old Broad Street, in the City of
London, Electrician, for an Invention of "IMPROVEMENTS IN THE CONSTRUCTION
OF APPARATUS FOR EFFECTING ELECTRICAL MEASUREMENTS."
PROVISIONAL SPECIFICATION left by the said John Clement Cuff at the
Office of the Commissioners of Patents on the 24th May 1881.
JOHN CLEMENT CUFF, of Old Broad Street, in the City of London, Electrician.
"IMPROVEMENTS IN THE CONSTRUCTION OF APPARATUS FOR EFFECTING ELECTRICAL
MEASUREMENTS."
This Invention relates to what are known as "resistance boxes," the object of
the Invention being to render these boxes more easy to use, to increase their
efficiency, and by simplifying their construction to reduce greatly the cost of
production.
Hitherto in winding resistance coils the wires have been wound on double in
order to obviate inductive effects, but this mode of winding has disadvantages
inasmuch as the ends of the wires are wound on in close proximity, thereby risking
leakage. I now propose to wind the coils with a single wire spirally, and reverse
the direction of the winding in every layer, whilst between each layer of wire is
placed a layer of insulating material. By this mode of winding I am enabled to
keep the end portions of the wires at a distance from each other, thus obviating
leakage. In order to more effectually insulate the bobbins from one another I fit
into the end of each bobbin a hollow plug, which will serve to remove them from
the base plate, or the bobbins may be made with a shoulder or flange for the same
purpose.
Each bobbin is supported by means of a brass rod which passes through and is
suitably fixed in the base plate. The upper end of this rod forms a contact stud,
and the lower end is flattened and bored to receive a cross pin, which retains in
place a block of vulcanite. This block is pressed against the pin by a spiral spring
mounted on the rod and inside the bobbin. The cross pin when inserted in its
place underlies a projection in the vulcanite block, and with it forms a clip to grip
one end of the wire on the bobbin, the other end of the wire being soldered to the
cross pin of an adjacent bobbin.

page_text: By the use of the clip above referred to I am readily enabled to adjust the length
of the wire on each bobbin when in place. I arrange the bobbins in rows
representing units, tens, hundreds, thousands, and so on.
In order to bring the required resistance into circuit I arrange above the base
plate and immediately over the rows of contact studs brass or other suitable bars,
which are held securely in place by strong spiral springs and stirrups or links.
Sliding freely upon each of these bars is a vulcanite block faced on the under-
side with a metal plate. This plate as the block is slidden along makes contact
between it and the contact studs in that particular row.
This arrangement of spring stirrups or links not only secures perfect contact, but
allows of the ready removal of the bars and blocks for cleaning purposes. The
circuit is made through the bars and stirrups with the next row of coils or with a
binding post.
The apparatus as above described may be used simply as a variable resistance,
or it may be with a Wheatstone bridge constructed in the same manner and fitted
in the same box for the purpose of making electrical measurements of cables and
line wires.
The action of the apparatus is the same as that of other forms now in use for
similar purposes, and will not need further description.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said John Clement Cuff in the Great Seal Patent Office on the
24th November 1881.
JOHN CLEMENT CUFF, of Old Broad Street, in the City of London, Electrician.
* IMPROVEMENTS IN THE CONSTRUCTION OF APPARATUS FOR EFFECTING ELECTRICAL
MEASUREMENTS."
This Invention relates to what are known as "resistance boxes," the object being
to render these boxes more easy to use, to increase their efficiency and durability,
and by simplifying their construction to reduce greatly their cost of manufacture.
In the accompanying Drawing Fig. 1 shews in plan view my improved resistance
box constructed with a Wheatstone bridge, the cover of the box being removed to
expose the apparatus to view.
Fig. 2 is a side elevation of the apparatus, the box and cover being shewn in
section, and Fig. 3 is an end view, the box and cover being also in section.
The apparatus as represented is complete in itself, and will require no removal
or addition of any parts for the adjustment of the apparatus on the putting of it
into working order.
Another advantage claimed for the apparatus is that its adjustment to test, for
example, the resistance of a cable may be read off with great facility, as may also
the variations of a battery current submitted to the test of the apparatus.
Referring to the Drawing, A is the base plate formed by preference of a slab
of vulcanite, pendent from which are the resistance bobbins B, B. These bobbins
are shewn as arranged in four rows representing units, tens, hundreds, and
thousands, and forming the resistance box proper, and a fifth row of resistance
coils B¹ is provided for the Wheatstone bridge.
Projecting downwards from the base plate A are rows of brass rods C, C*, the rods C
serving each to carry their respective bobbins B, B¹. The several rods C and C*
are firmly secured to the base plate, and are fitted at their lower ends with blocks
of vulcanite D. These blocks D are secured to their rods by metal pins & which
pass through the block and through an eye in the rod, and extend into a groove
formed lengthwise of the block. A transverse groove is made in these blocks, the
grooves in the block carried by the rods C serving to receive respectively one end
of the overlying coils B, B', which end lies in contact with its pin d, and through
it is brought into metallic connection with the rod C.
To ensure the maintenance of the contact of the coil with the pin da coiled
spring bis introduced into the bobbin, as shewn in the detached view Fig. 4, which
spring bears against the block D, and thus causes it to press the wire in its groove
tightly against the pin d; a counter pressure on the block will provide for the
facile release of the wire, or for its introduction into the transverse groove, a little
play in the pin hole of the block being provided for that purpose.
A similar provision is made for obtaining an elastic pressure of the blocks
carried by the rods C* for the purpose to be presently explained, the coiled spring
being in this instance contained in an empty bobbin, which serves only as a point
of resistance for the coiled spring.
I have said that the pin d makes metallic contact between the wire of the
bobbin which it holds in place and the rod which carries the bobbin ; it is also
connected by means of solder to the wire of the next adjacent bobbin of the row,
and it is by this means that all the bobbins B of each of the four rows are
connected together.
The upper ends of the rods C and C* form contact studs, and each row of these
rods is overlaid by a flat bar of brass or other suitable metal, the ends of which

page_text: rest in transverse notched bars E¹ of vulcanite. E, E, are the bars of the resistanco
box proper, and F is the bar of the Wheatstone bridge. These bars E are held
down by stirrup shaped brass links c, e*, to the lower ends of which are attached
coiled springs el, e, connected to a fixed point on the underside of the base plate,
and serving to put a downward pressure upon the bar.
Mounted on each of these bars E is a sliding block E2 of vulcanite, which is free
to slide on its bar by the pressure of the fingers of the operator, and carries at the
underside of the bar a contact plate of phosphor, bronze, or equivalent material.
These blocks are formed with a knot to facilitate their manipulation, and by sliding
them along their bars any number of the coils underlying the bars may be put into
or thrown out of circuit, as will be hereafter more fully explained. The links e are
severally connected by wires e², e², with one of the pendent rods C, which wires
are inserted in the cross grooves of the blocks D, and are clipped by the coupling
pins d.
The links e thus serve to maintain the electric connection between the rows of
bobbins B. The better to ensure this, these links are provided (see the detached
view, Fig 5) with a platinum contact pin for bearing upon the brass bar E.
When all the vulcanite blocks E' are drawn into contact with the studs C*, the
whole of the coils are out of circuit, and as they are severally moved to the right
band all the coils between the studs C* and the studs in contact with the metallic
facings of the blocks will be in circuit, the remainder (if any) being out of
circuit.
&
The coils it will be seen are numbered from left to right, and as cach coil
represents a given amount of resistance, the total amount of resistance put into the
circuit will be easily read off. G and G¹ are the terminals, and represent the points
of ingress and egress of the current under ordinary circumstances. If, however, it
is desired (for example) to test the locality of a fault" in a cable, I use the
Wheatstone bridge which is permanently coupled up with the resistance apparatus
proper in the same manner as the rows of coils B are connected together. In that
case the terminal G* will be used in place of the terminal G.
Fitted to the bar F which carries the terminal are two sliding blocks of
vulcanite F1, F2, similar in construction to the sliding blocks E on the bars E.
The bar F is held down on the vulcanite notched bars E¹ by links similar to the
links e*, and the sliding blocks F1, F2, are each capable of traversing one half or
nearly so of the length of the bar F for the purpose of bringing the bar into
communication with one or other of the resistance coils B' on either side of the
centre of the bar. The line of coils B' is divided into two sets, the several wires
of the one set being connected through a wire h with a terminal H, and the several
wires of the other set being connected through a wire h¹ with the terminal H¹.
The opposite ends of these coils of wire are in electric communication with their
respective pendent rods C, as explained with reference to the resistance coils B.
The terminal H is connected by a wire h³ with the terminal G, and thus the
battery may be coupled with the resistance box through the terminal G³ or G, as
circumstances may dictate.
For the purpose of bringing the Wheatstone bridge into use it will be necessary
to connect the two terminals H and H¹ by a circuit including a galvanometer, as
indicated by the dotted lines in Fig. 1, and to connect, say, the cable to be tested
with the terminal H¹.
Supposing it is intended to measure the electro motive force of a given electric
battery, I connect one pole of that battery with the terminal G, and the other pole
with one of the terminals G', placing within the circuit a galvanometer. I then
by traversing the sliding blocks E put within the circuit a greater or lesser
number of resistance coils, increasing or diminishing the resistance until the
galvanometer indicates the amount of resistance the battery is capable of working
through.
The positions at which the several sliding blocks E² are arrested will be indicated
by the figures opposite which they stand, and thus the reading off of the amount

page_text: of resistance thrown into the circuit becomes a simple operation. In Fig. 1 the
sliding block on the first bar E from the bridge stands at 4, that of the second bar
at 1, that of the third at 5, and that of the fourth bar at 8. The reading thorefore
of the resistance in this circuit will be 4158 ohms.
Supposing now the apparatus is used to test a fault in a cable, the Wheatstono
bridge will be brought into the battery circuit, as already explained. If the cable
resistance is within the range of the coils in the resistance box, then the sliding
blocks on the bar F will be placed at equal distances from the central terminal G³,
as shewn in the Drawing, the actual amount of resistance will then be ascertained
in the manner above explained.
But if the resistance to be measured exceeds the range of the box, then the
resistance of the bridge on the side to which the unknown resistance is attached
must exceed the resistance of the other side of the bridge to which the resistance
coils are attached. Thus, for example, if the resistance to be measured is about
80,000 ohms, it is clear that as the box only has a total resistance of 9999 ohms
(which may be regarded in practice as 10,000 ohms), the coil in the bridge between
G² and H¹ must be made of greater value than that between G³ and H. Thus, if
the sliding block F' is put to 100 and the sliding block F2 to 1000, then the
reading on the box must be multiplied in the same ratio as that of the coils in the
bridge, or in this case by 10. Thus, if a balance on the galvanometer is obtained
when the reading on the box is 4158, it must in this case be written down as
41,580. By this means a multiplying power of 1000 can be obtained by putting
one of the sliding blocks at the extreme end of the bridge, and thus the box will
measure up to 1000 × 10,000 or up to 10 megolims, that is, to 10 millions of
units.
Again if it is desired to measure a resistance less than one ohm, that being the
lowest resistance coil in the box, the resistance of the bridge on the side to which
the unknown resistance is attached must be made less than the resistance on the
other side of the bridge to which the resistance coils are attached. Thus, for example,
if the resistance to be measured is about the one tenth of an unit (or 1 ohm) 1000
must be put in the bridge between G and H, and 10 between G and H', then
whatever is the reading on the box when a balance is obtained must be divided by
100; thus, if in this case the box reading be 184, it must be written down as 1.84,
and so on.
I will now explain the manner in which I construct my resistance bobbins.
Hitherto in winding resistance coils the wires have been wound on double in order
to obviate inductive effects, but this mode of winding has the disadvantage of not
securing good insulation.
I now propose to wind the coils with a single wire helically and reverse the
direction of the winding in every layer, placing between each layer of wire a layer
of insulating material. By this mode of winding I am enabled to bring out the
ends of the wire at the opposite ends of the bobbin. The mode above described
of coupling the lower end of the bobbin wire with the supporting rod affords an
important incidental advantage, viz., the exact adjustment of the length of the
wire, which as it is brought under the nip of the coupling pin & may be altered
in length by simply sliding the end backwards or forwards under the nip of
the pin.
In order to more effectually insulate the bobbins from one another, I fit into the
end of each bobbin a hollow plug (see the detached view, Fig. 4) which will serve
to keep them clear of the base plate, or the bobbins may be made with a shoulder
for the same purpose.
To prevent the bars E and F from shifting longitudinally when in place, I
groove them transversely at one end to receive the holding down links e*. This
arrangement of links not only secures perfect contact, but allows of ready removal
of the bars and sliding blocks for cleaning purposes.
The base plate A it will be understood is secured by screws to the box, and it is
notched out to permit of hook-shaped plates fitted to the cover dropping down

page_text: into a position to bo slidden under the base plate, and thereby act as hold fasts.
The cover is formed with a hinged portion which overlies the end of the apparatus
where the links e are situated. This hinged portion I fit with a lock for securing
the cover in position. Notches are made in the cover for the several connecting
wires to pass through.
Having now set forth the nature of my Invention of "Improvements in the
Construction of Apparatus for Effecting Electrical Measurements," and explained
the manner of carrying the same into effect, I wish it to be understood that under
the above in part recited Letters Patent I claim,-
-
First. The arrangement of apparatus above described, whereby through the
shifting of a sliding contact plate or its equivalent resistance coils may be thrown
into or out of circuit, for the purpose above set forth.
Secondly. The manner above described of constructing and adjusting resistance
coils.
Thirdly. Arranging resistance coils in groups, and connecting such coils and
groups one with the other, in the manuer and for the purpose above set forth.
Lastly. The arrangement of Wheatstone bridge, as above described.
In witness whereof, I, the said John Clement Cuff, have hereunto set my
hand and scal, the Twenty first day of November, in the year of our Lord
One thousand eight hundred and eighty one.