Improvements in Electric Resistance Boxes or Coils.
Year: 1893

page_text: Date of Application, 10th Jan., 1893-Accepted, 29th July, 1893
COMPLETE SPECIFICATION.
[Communicated from abroad by EDWARD WESTON, of Newark, New Jersey,
United States of America, Electrician.]
Improvements in Electric Resistance Boxes or Coils.
I, HENRY HARRIS LAKE, of the Firm of Haseltine Lake & Co., Patent Agents,
of 45 Southampton Buildings, in the County of Middlesex, 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 :-
The invention relates to resistance boxes or coils and certain improvements
therein.
Figs. 1, 2 and 3 exhibit a form of apparatus in which the resistance in a circuit
may be modified by changing the approximation of a series of suspended plates.
Fig. 4 represents two or more series of resistances and mechanism for changing
the relation of one or more resistances of each series, to a circuit including both
series; the said mechanism being constructed and organized so that when it
establishes circuit through a given resistance of one series it simultaneously and
automatically cuts out of circuit an equal resistance of the other series.
Figs. 5, 6, 7, 8 and 9 represent an improved form of bridge or resistance coil for
making electrical measurements in which equal variations in. resistance can be
obtained by the use of fewer coils than is commonly employed in instruments of
this class and whereby the coils are arranged in more compact form and smaller
compass. Said bridge is also constructed so as to obviate error from leakage of
current in the manner hereafter described.
Referring first to the apparatus illustrated in Fig. 1, which is a transverse
section on the line X X of Fig. 2, Fig. 2 a plan view and Fig. 3 a longitudinal
section on the line Y.Y of Fig. 1, in which figures similar numbers of reference
indicate like parts: The frame consists of the base 1, uprights 2, cross-pieces 3 and
longitudinal upper bars and 5. On bar 4 is an arm 6, to the end of which is
fastened, by screws 7, a brass block, 8. Block 8 has a central aperture and has
secured to it a strip of spring metal, 9, which supports the metal disk 10. The
disk 10 carries an annular plate of carbon, 11. Secured to bar 5, adjacent to arm 6,
is a metal arm, 12, parallel to arm 6, which carries a brass block similar to block 8,
which block carries a spring similar to 9 and a metal disk similar to 10, to which
metal disk is attached a carbon disk similar to 11. The instrument may contain
any number of arms, such as 6 and 12, alternating so that there is produced a series
of annular metal disks concentrically disposed one in rear of the other supported by
springs and mutually insulated. Each disk carries a carbon plate which faces the
adjacent disk. The central openings in the disk are in line. The central openings
in block 8 are also in line and receive a metal rod, 13, enclosed in an insulating
sleeve, 14, and fastened at its ends in the frame of the apparatus. This rod holds
the plates in correct alignment and prevents displacement. 16 is a screw-shaft
revolving in bearings, 15, on the base 1. On this shaft are reverse screw-threads
receiving nuts 17, 18, secured to which are flanged compression-heads, 19 and 20,
the edges of the flanges of which heads bear against the outermost annular disks, 10,
of the series. As the screw-shaft passes through the central openings of the disks
its reverse threads, when a hand-wheel, 21, is turned, causes the nuts 17 and 18, and
hence the heads 19 and 20, to move toward or away from one another; and thus
the disks may he brought into more or less close contact. The separation of the
disks is effected by the elasticity of the spring supports 9. The diameter of the
disk openings being larger than that of the screw-shaft allows of free movement of
the disks. By this device a series of carbon or other plates of high-resisting

page_text: :
.
material may be subjected to a degree of compression which, by the gradual action
of the reverse screws, can be nicely regulated; and thus the amount of resistance
offered by the series of plates can be accurately controlled.
The electrical connections are as follows: On bars 4 and 5 are metal plates, 22
and 23, having projections, 25. These come opposite the inner ends of the short
arms, as 12, while the inner ends of the long arms, as 6, lie between said portions.
Between the extremities of arms 12 and those of projections 25 are holes to receive
metal blocks, 27. Similar plug-holes exist between arms 6 and the body portion of
plates 22 and 23. In plates 22 and 23 are two sets, 24 and 26, of four binding-
screws, Fig. 1. With plugs 27 in place, the current entering at post 24 passes to
plate 22 and to arms 6 or 12 supported by bar 4, thence to the disks carried by said
arms, thence to the adjacent disk carried by arms supported by bar 5, to said arms,
to plate 23 and binding-post 26. The current then passes from one disk to its
neighbour, and then out, the disks being connected in multiple arc; but by suitably.
adjusting the plugs, any number or all of the disks may be connected in series, so
that the resistance of any number of them can be interposed in circuit. In practice,
the plugs are first adjusted to connect the disks as desired in series or otherwise,
and then the screw-shaft is rotated to move the disks into more or less close
contact; and in this way to regulate the resistance offered.
Referring next to Fig. 4, a is a box containing the resistance coils diagram-
matically indicated at b. On it are two sets of contact-plates, c' c² c c and d¹ d'
d³ d. The resistance coils bare interposed between adjacent plates. The plates c
to and coils b constitute one independent set of resistances, and the plates d¹ to d
and their coils b, another set. The resistance coils interposed between the
plates and also between the plates d', are each of a resistance of 1000 ohms ;
those between the plates c³ and the plates d³, are each of a resistance of 100 ohms
those between the plates 3 and the plates d³ are each of a resistance of
10 ohms; and those between the plates c and the plates d', are each of a resistance
of 1 ohm.
;
In each of the series c¹ d¹, c² d², c³ ³, there are ten contact-plates which may be
numbered from 0 to 9 successively, as shown. In the series c and d there are
eleven contact-plates numbered from 0 to 10 successively, as shown. The plates c d
are disposed about the circumference of a circle; and the other series c² d², c³ d³
and cd are similarly disposed. Pivoted at the centre of each circle on the
circumference of which are disposed the plates c² d², c³ d³ and c d, is a bar, f, f³, ƒ^‚
of insulating material, and supported on this bar are diametral arms g³ h², g³ h³,
and 9 h. The arms of each pair as g² h², are thus insulated from one another.
Pivoted at the centre of the circle around the circumference of which are
disposed the plates c¹ d', is a bar f¹ of metal, the extremities of which form
armis g' ' corresponding to the similar arms g² ², &c., as above described. At the
extremity of each arm and bearing upon each series of plates, is a contact
spring, i.
The circuits in the instruments are as follows. The first circuit is from the
binding post 1 to the plate 0 of the series c', thence through the several coils
:(one or more) and plates of said series to the arm g, thence by the flexible
conductor m' to the plate n³, thence to the series of plates 3 and their coils b to the
arm 93; thence by the flexible conductor m³ to the plate n², thence to the series of
plates and their coils to the arm g²; thence by the flexible conductor m² to the
plate n', thence to the series of plates c¹ and their coils 6, and thence to the arm g¹
to the pivot of said arm, and thence to the binding post o.
The second circuit proceeds similarly from the binding post 1¹ to the plate 0
of the series d', and through the several coils (one or more) and plates of said
series, to the arm h, flexible conductor p and plate q³; thence to the coils and
plates of the series ³, arm h³, flexible conductor p³ and plate 92; thence to the
coils and plates of the series d², arm 2, flexible conductor p² and plate q'; thence
to the coils and plates of the series d¹, arm h¹ and binding post o.
The plates q', 92, 93, connect with binding posts r¹, r², Between each pair of

page_text: plates as q, n', are openings to receive metallic plugs of the usual kind, which
establish electrical communication between the said pair of plates. If one circuit.
terminal is connected to the binding post o, and the other be connected to the post r¹,
and the plug be inserted between plates g', n', it will be evident that only the series of
plates cd will be in circuit. If the terminal be connected to post 2 and the plug be
inserted between plates n² 92, then the series of plates c¹ d' and c² d² will be in circuit.
If the terminal be connected to post and the plug be inserted between plates n³ ³
then the series of plates c¹ d', c² d² and c³ ³ will be in circuit. If no plugs be inserted
and one terminal is connected to post o and the other to post 1, then the plates of
series cc2c3 c4 will be in circuit. If no plugs be inserted and one terminal be
connected to post o and the other to post 1', then the plates of series d¹ d² d³ d¹²
will be in circuit.
The foregoing is sufficient to indicate the various changes which may be made in
the instrument.
;
For purposes of illustration in explaining the use of the instrument, assume the
contact arms to be disposed as shown in the drawing. Then the total resistance
offered by series c¹ is 9000 ohms; by series c², 900 ohms; by series c³ 90 ohms
and by series c 9 ohms: or in the aggregate 9999 ohms. If the arm g¹ were
moved to plate 10 of series c, then the total resistance would be one ohm more, or
10,000 ohms.
On the other hand, if all the coils b of series d' d' d³ d' are cut out of circuit, the
aggregate of both resistances is (as desired) 10,000 ohms.
If it be desired to cut out 1000 ohms from one series e¹ c² c3 c4, which, for brevity,
I will hereafter term R, while at the same moment adding 1000 ohms to the
series d' d² d³d, hereafter termed R', clearly, all that is necessary is to move the
arm g' from the plate 9 of series c' to the plate 8. The arm h³ will necessarily
move from the plate 0 of series d¹ to the plate 1.
The other parts remaining as before, the
8999 +1 = 9000 ohms; and the resistance in R¹ will read 1000 ohms.
aggregate resistance will still be 10,000 ohms.
resistance in R will read
And the
If it be desired to remove 100 ohms from R, the arm 92 is moved from the plate 9
of series ³ to plate 8; and simultaneously the arm 2 moves from plate 0 of
series to plate 1, and thereby adds 100 ohms to series R¹. And generally, as will
be evident, the movement of the arms g¹¹ from one plate of series c¹ d¹ to
another adds one or more thousand ohms to R¹ and subtracts an equal amount
from R; and by the movement of the arms g² 2, 93 h³ and 9* *, the hundreds, tens
or unit ohms are added and subtracted in like manner.
Referring next to Figs. 5, 6, 7, 8, 9, Fig. 5 is a diagram of the Wheatstone-
bridge. Fig. 6 shows a diagramatic view of the connections with the resistance
coils. Fig. 7 is a plan view of one set of coils with their contact-plates. Fig. 8 is
a longitudinal section and Fig. 9 is a plan view. In Fig. 5, M, N represent the
arms of the bridge in which are placed fixed resistances. In arm R is the variable
resistance and in X the unknown quantity to be measured. O is the galvanometer
and P the battery in the bridge. Similar parts are correspondingly lettered in
Fig. 6, so that the bridge-connections therein will be easily understood. Beginning
at the contact-plate 31, the arm M meets the arm N extending from contact-
plate 32. From the point of junction of M N, wire 33 goes to binding-post 34.
The battery P connects with binding-posts 34, 35. From binding-post 35 a
wire, 36, containing contact-key 37, connects with plate 38, which connects with a
series of resistance-coils, R, not shown in Fig. 6. The other end of this series of
resistance-coils connects with plate 39, which, by wire 40, connects with binding-
post 42. In wire 40 is a contact-key, 41. Galvanometer O connects with posts 42.
and 43. Posts 44 and 45 connect with unknown resistance X. Post 45 connects,
by wire 46, with wire 36. Post 44 connects, by wire 47, with plate 48 and by
wire 49 with post 43. 50 is the case, having a cover, 51. 52 is a platform of
ebonite on which are fastened the contact-plates 39, 70, 71. Resistance coils, 53,

page_text: are supported on rods, 54, by nuts, 55. Connection between the metal plates to cut
out the coils is effected by plugs, such as 57 which passes through an opening in
the ebonite platform and enters a wedge-shaped aperture between the plates.
Referring now to Fig. 9, the coils 58 are ratio-coils and are connected all at one
end to plate 48 and each at its opposite end to that which is fastened to the bar 48
is fastened to the small contact-plates 59, 60. The first of the series of resistance-
coils in the variable resistance is represented at 61, the second series at 62, the
third at 64 and the fourth at 65. These may represent units, tens, hundreds and
thousands of ohms respectively. The series 61 is supported on the bar 39, the
second series, 62, is supported on the bar 70. Between the bar 39 and the bar 70.
there are five smaller contact-plates, 71, 72, 73, 74, 75. The first coil of series 61
has its terminals connected to plate 70 and plate 71, the second coil is connected
to plates 71 and 72, the third to plates 72 and 73, and so on to the fifth coil, which
has its terminals connected to plates 75 and 39. Suppose that each coil, except
the last of the series which connects plates 39 and 75, to be of one ohm resist-
ance, as marked in Fig. 7, and that the coil thus excepted has five ohms.
resistance. Suppose the current to come in at the arrow 76 of Fig. 7, and go out
at the arrow 77. If a plug is inserted in the hole marked zero and plates 39
and 70 be connected, the current will pass through no coils. If the plug be
placed in the hole marked 1, then the current will go through the coil between
the plates 70 and 71, which is one ohm, and similarly, if the plug be placed in
the holes marked 2, 3, 4, 5, Fig. 7, the current will, in each case, pass through
one more coil, and thus the resistance to be gradually increased from one
to five ohms. To go to six ohms, the plug is placed in the hole marked 6, when
the current will pass through the plate 70 to the plate 74, and thence through
one ohm resistance to plate 75, and thence through five ohms resistance to
plate 39. To obtain seven ohms resistance, the plug is placed in hole 7; and
finally, to make ten ohms resistance all of the holes are left unplugged and the
plug is simply put in a blind hole, which is here marked 10, and which is
merely an opening in the bar 70. This arrangement of contact-plates is repeated
with all the other series of coils, and it allows of obtaining, by the use of only
six coils, all the variations in resistance which commonly require ten coils, with
the consequent economy of expense and greater accuracy in manufacture.
Referring now to Fig. 8, it will be seen that the contact-plates 39, 70, 71, &c.,
are located on the under side of the platform 52, and that both the coils and the
plates are therefore wholly enclosed within the containing case 50. It is found
that when the contact-plates are arranged on the upper side of the ebonite platform,
as is now usually done, that the instrument becomes subject to serious error from
the following causes: First, the sulphur used in rubber or ebonite preparations,
combining with the oxygen of the air, forms an acid film on the upper surface of
the supporting platform which is conducting and which allows the leakage of a
current from one contact-plate to another when the plugs are out. It is impossible
to avoid this as long as the upper surface of the rubber plate is exposed to air and
light; and this leakage is sufficient to disturb the accuracy of measurements unless
great precautions are taken to prevent it. Another difficulty is that the constant
abrasion of the plugs in their seats between the contact-plates gradually wears off
small particles of metal which accumulate in the many angles and at the bottom of
the many channels between the contact-plates, and thus again form a means of
causing leakage of the current. By arranging the contact-plates on the under side
of the ebonite platform, it will be plain that any filings, dust, or foreign matter
will tend to fall out of the channels or angles, and therefore cannot remain_or
accumulate in said. channels. This arrangement of the contact-plates on the under
side of the ebonite platform, which allows of the whole of the operating part of the
instrument being enclosed and protected from light, air and dust, besides avoiding
the difficulty due to the lodging of foreign conducting particles between the plates,
is one of the important features of my invention.

page_text: Having now fully described and ascertained the nature of the said inven-
tion, and in what manner the same is to be performed, as communicated to me
by my foreign correspondent, I declare that what 1 claim is
1. A resistance apparatus containing a series of bodies of conducting material
suspended on springs and arranged in circuit, and provided with a screw or
equivalent means for bringing them into more or less close contact against the
elasticity of the suspending springs, as hereinbefore described and more particularly
as exhibited in Figures 1, 2 and 3.
2. A resistance apparatus containing two or more series of resistances and
mechanism for changing the relation of one or more resistances of each series to a
circuit including both series; the said mechanism being constructed and organized
substantially as illustrated in Fig. 3, so that when it establishes circuit through a
given resistance of one series, it simultaneously and automatically cuts out of
circuit an equal resistance of the other series.
3. The construction and arrangement of the resistance coil or bridge and the
disposition of the contact-plugs and contact-plates therein substantially as described
and as illustrated in Figures 5 to 9.
Dated this 10th day of Tenuar 1902
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.