A New or Improved Electrical Resistance Measuring Instrument.
Year: 1898

page_text: Date of Application, 26th Nov., 1898-Accepted, 9th Sept., 1899
COMPLETE SPECIFICATION.
A New or Improved Electrical Resistance Measuring Instrument.
We, GEORGE TILDEN HANCHETT and FREDERICK BRITTAN SAGE, of Times Building,
in the City, County, and State of New York, United States of America, 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:-
This invention relates to electrical resistance measuring instruments.
The object of the invention is to provide a simple form of instrument which shall
be cheap to construct, sufficiently accurate for all practical purposes and in which the
operation of measuring resistances is made very simple. Incidentally in carrying out
our invention, we have devised a scale which indicates directly, the number of ohms
in the measured resistance and thereby eliminates the necessity of performing calcula-
tions after a balance is obtained. The principal feature of our invention is its com-
pactness and the simplicity with which measurement may be made.
In the accompanying drawing :-
Figure 1 is a perspective view of the apparatus.
Figure 2 is a sectional view of the same.
Figure 3 is a diagram of the circuits.
The apparatus, as usual, is contained in a suitable box A having a cover a only one
corner of which is shown by Figure 1. The cover being opened discloses a face-
board B, and beneath this the box is divided into two compartments C and D
respectively, the former containing a battery C¹, and the latter serving as a housing
for a telephone receiver, a circuit closer, and flexible conductors to which they are
connected. For the removal of these devices, the box A has a slide-door a¹ opening
into the compartment D. The flexible cord referred to, passes through an opening in
the partition between the two compartments and thence leads to the proper points
for establishing the circuits hereinafter described. The resistance wire commonly
used with these instruments and termed the "known resistance" is a small coil of
fine wire c, deposited in a cylindrical chamber c¹, formed in the face-board B.
Along the middle of the face-board is a strip e, upon which the operator may rest
his hand while testing. On each side and parallel to this is stretched a high resis-
tance wire f,f. Wire f, is stretched from copper block g, to the copper cross-bar h,
and wire fi, is stretched from the cross-bar h, to the copper-block 2, a continuous
circuit thus being formed from block g, through the wire f, bar h, wire f, to block i.
At one end of the face-board, preferably in line with the strip e, is fixed a copper-
barj, and opposite to it, a plurality of copper blocks k, with sockets between the bar
and blocks for connecting them by means of a plug. Two binding posts m, and n,
are provided between which the circuit or resistance to be measured is to be con-
nected. One of these posts connects with the block g, while the other connects with
the bar j.
The telephone instrument and circuit closer above referred to are indicated by T
and K respectively. The circuit-closer consists of a handle of insulating material
having a metallic point or "toucher" t, at its extremity and two circuit terminals r,

page_text: and respectively which may be electrically connected together by two metallic
springs 8, and 81, attached to a metallic collar s².
The circuits are as follows: the battery C¹ is connected between the blocks g, and i,
its circuit being normally open between the points r, and r¹, on the circuit-closer K,
but closed when the operator presses the springs & and s¹, against r and r¹. From
block g, wires f, and f¹ extend to block i, forming two arms of the bridge, the other
two arms being formed respectively by the known-resistance c, and the unknown-
resistance x, between the points m, and n. The bridge circuit extends from a point
between the resistances c, and x, through the telephone receiver T and through K to
the toucher t.
To measure a resistance or make a test, the unknown resistance or circuit is con-
nected between the binding posts m, and n: then with the telephone at the ear and
the circuit-closer K, in hand, the operator while pressing the springs s, and 81, against
contacts r,, touches the wire f, or f¹, at different points until he finds a point where
the touching is not accompanied by a sound from the telephone. This is an
indication of a balance of resistance between the two sides of the bridge, and since
the resistance off, f¹ and c is known, the value of x, may be determined therefrom
by the usual formula. But when using the special scale we have devised the
position of the toucher on the wire f, or f¹, indicates at once the resistance of x in
ohms.
Referring to the scale employed, the ratio of the portions of the wire on either side
of the toucher is equal to the ratios of the known and unknown resistances. The
known resistance may be 1, 10, 100 or 1000 ohms.
The scale is divided according to the following law :—
and the point corresponding to 50 ohms is 5 inches from the end of the scale.
As before explained the scale is, for convenience, in two parts, one on each side of
the apparatus, the two parts being connected by the copper cross bar h.
The object of the plurality of plugs and the bar j, is to enable the operator to
alter one of the known resistances so that it shall not be too high or too low for the
unknown resistance. The three divisions shown provide for the use of 1 ohm,
10 ohms, or 100 ohms; we are obviously not limited to any particular sub-division of
this resistance, but whatever number of sub-divisions is provided for, a corresponding
number of scale values must be provided, thus three sets of figures may be employed
with each division upon the scale, one set for one ohm of known resistance, another
set for 10 ohms of known resistance, and the third set for use with a known
resistance of 100 ohms. Each set of figures may be differently coloured, as, for
example, one set in red for 1 ohm of known resistance, one set in black for 10 ohms,
and one set in chocolate for 100 ohms.
It is obvious that any other suitable form of indicating instrument may be
substituted for the telephone.

page_text: 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 :-
1. In an electrical resistance measuring instrument, the combination of the circuits
thereof with a circuit-closer for the battery and a circuit-closer for the bridge both
attached to a single movable handle substantially as and for the purpose set forth
and as illustrated by the accompanying drawings.
2. In an electrical resistance measuring instrument of the "slide-wire" type, the
combination with the high resistance stretched wire forming one side of the circuit
of a battery, of a "toucher" and battery circuit closer mounted together and
movable, and an indicator in circuit with the "toucher " substantially as
described.
3. In an electrical resistance measuring instrument the combination of two
metallic blocks or terminals insulated from each other, a metallic bar and two wires
stretched between the respective blocks and the bar, said wires forming in series one
side of the bridge circuit, a movable "toucher" and an indicating instrument in
circuit therewith, substantially as hereinbefore described and as illustrated by the
accompanying drawings.
4. In an electrical resistance measuring instrument the combination of a resistance
wire forming one side of the bridge, a movable indicator circuit closer and a scale
reading directly in ohms, substantially as described and as illustrated by the
accompanying drawings.
5. In an electrical resistance measuring instrument the combination with the
circuits thereof of a bridge circuit-closer and a battery circuit-closer combined
into a single movable device, substantially as illustrated by the accompanying
drawings.
6. An electrical resistance measuring instrument constructed arranged and
operated substantially as herein before described and as illustrated by the accom-
panying drawings.
Dated this 91st day of New Low 1000