A METHOD OF AND APPARATUS FOR DETERMINING THE TIME CONSTANT OF AN ELECTRICAL CIRCUIT
Year: 1884

page_text: I, THOMAS HOLMES BLAKESLEY of 25 Queen Anne's Gate Westminster in
the County of Middlesex, Civil Engineer do hereby declare the nature of my
invention for "A METHOD OF AND APPARATUS FOR DETERMINING THE TIME
CONSTANT OF AN ELECTRICAL CIRCUIT "to be as follows:-
My invention relates to means of determining the time constant of an electrical
circuit, whether that result from self induction, mutual induction, from connection
with a condenser or from any of these or other causes acting together.
I cause a permanent magnet to revolve rapidly within an annular coil which is in
the plane of the axis of revolution of the magnet and can be turned round that
axis and set at any point indicated on a scale. On the axis of the magnet is
a commutator consisting of two insulated plates against which bear brushes or
rubbers fixed in position and connected to a galvanometer. The annular coil is
connected in the circuit, whose time constant has to be determined, and to the two
plates of the commutator. The revolution of the magnet sets up in the coil
alternating undulating currents which are converted by the commutator so as to
be indicated on the galvanometer. By turning the coil round relatively to the
diametral plane passing through the contacts of the commutator brushes, and
observing the indications on the galvanometer, knowing also the angles which the
plane of the coil makes with the plane of the brush contacts and the speed at
which the magnet revolves, I can compute the time constant of the circuit. It is
generally convenient, for simplifying computation, to turn the coil to such position
that the galvanometer indicates zero. Instead of causing the magnet to revolve, it
may be set in various positions and held stationary while the coil revolves, and the
connections of the circuit and of the galvanometer to the commutator plates and its
brushes may be inverted.
Instead of varying the position of the coil relatively to the brush contacts,
various resistances may be introduced into the circuit, and from the various
indications of the galvanometer resulting from their introduction, the time constant
can be computed.
ABEL & IMRAY,
Agents for the Applicant,
28, Southampton Buildings,
London, W.C.

page_text: I, THOMAS HOLMES BLAKESLEY of 25 Queen Anne's Gate, Westminster in
the county of Middlesex, Civil Engineer, do hereby declare the nature of my
invention for "A METHOD OF AND APPARATUS FOR DETERMINING THE TIME
CONSTANT OF AN ELECTRICAL CIRCUIT" and in what manner the same is to be
performed to be particularly described and ascertained in and by the following
statement-
My invention relates to means of determining the time constant of an electrical
circuit, whether that result from self induction, mutual induction from connection.
with a condenser, or from any of these or other causes acting together.
I cause a permanent magnet to revolve rapidly within an annular coil which is
in the plane of the axis of revolution of the magnet and can be turned round that
axis and set at any point indicated on a scale. On the axis of the magnet is
a commutator consisting of two insulated-plates-against-which-bear-brushes-or-
rubbers fixed in position and connected to a galvanonometer. The annular coil is
connected in the circuit, whose time constant has to be determined, and to the two
plates of the cominutator. The revolution of the magnet sets up in the coil
alternating tindulating currents which are converted by the commutator, so as to
be indicated on the galvanometer. By turning the coil round relatively to the
diametrical plane passing through the contacts of the commutator brushes, and
observing the indications on the galvanometer, knowing also the angles which the
plane of the coil makes with the plane of the brush contacts and the speed at
which the magnet revolves, I can compute the time constant of the circuit. It is
generally convenient for simplifying computation, to turn the coil to such position
that the galvanometer indicates zero. Instead of causing the magnet to revolve, it
may be set in various positions and held stationary while the coil revolves, and the
connections of the circuit and of the galvanometer to the commutator plates and its
brushes may be inverted.
Instead of varying the position of the coil relatively to the brush contacts,
various resistances may be introduced into the circuit, and from the various
indications of the galvanometer resulting from their introduction, the time constant
can be computed.
Fig. 1 of the accompanying drawings is a plan of apparatus according to my
invention, fig. 2 being an elevation of the adjustable commutator brushes A is
a coil within which a magnet B is mounted on an axis C which coincides with a
diameter of the coil and which is caused to revolve rapidly by a band on a pulley D
or otherwise. On the axis are fixed two insulated rings E and F, against which
bear rubbers or brushes ef. Between the rings E F there is also fixed insulated on
the axis a ring G divided at opposite points of its circumference into two distinct
parts, each part having a connection to one of the rings E F and having bearing
against it a brush or rubber H K. These are fixed insulated on a ring L which
can be turned round the axis C, for which purpose, as shewn in fig. 2, it is fitted
in grooves in a casing M. The ring L and the arcs of the casing M aro accurately

page_text: graduated; preferably with vernier divisions. There may be on the axis C several
sets of the rings E F G and their brushes, according to the number of circuits
which it is desired to examine. When one external circuit such as N is to
be examined, one end of it is connected through the coil A to one of the two
brushes ef and the other end is connected to the other of these brushes; the two
brushes HK are connected to a galvanometer. The axis C with the magnet B
being then caused to revolve rapidly, the galvanometer is affected. On then
turning the ring L round, so as to bring the bearing points of the brushes H K to
such a position that the galvanometer gives some known indication or zero, the
angle which this position has to the plane of the coil A can be observed as shewn
by the divisions on L and M, and this angle, the speed of revolution, the resistance
and the galvanometer indication form data by which the time constant of the whole
circuit including the coil A can be computed. By connecting the two ends of the
coil A to the brushes ef and computing for this alone, the effect of the coil A itself
is known and can be eliminated in other cases.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is
1, The herein described method of determining the time constant of an electrical
circuit by ascertaining the position of the phase of the current in the circuit
relatively to the phase of an electromotive force in that or in another circuit.
2, The construction of apparatus for determining time constants in electrical
circuits, substantially as herein described.