Improvements in Apparatus for Measuring the Frequency of Alternating or Pulsating Electric Currents, or of other Periodic Disturbances.
Year: 1895

page_text: Date of Application, 18th June, 1895
Complete Specification Left, 18th Mar., 1896-Accepted, 13th June, 1896
PROVISIONAL SPECIFICATION.
Improvements in Apparatus for Measuring the Frequency of
Alternating or Pulsating Electric Currents, or of other Periodic
Disturbances.
I, ALBERT CAMPBELL of 34 St. George's Square, Regent's Park, London,
N.W., Electrician, do hereby declare the nature of this invention to be as
follows:-
A piece of elastic material, which I shall call for convenience the "vibrator," is
mounted in such a way that by varying the relative positions of the vibrator &
part of the mounting the size can be varied of a portion of the vibrator which is
free to vibrate. This variation in size of the part free to vibrate is shown on a
scale by means of a pointer connected, either directly or, more usually, through
magnifying gear, with the vibrator. The scale may be marked to read frequency
directly. The whole or part of the vibrator is of magnetic material. One or
more electro-magnets are arranged in proximity to the vibrator & can be excited
by being put in connection with the electric circuit whose frequency of alternation
or pulsation is to be measured.
To work the instrument, the size of the part free to vibrate is continuously
varied until by the action of the intermittent magnetic attraction a state of proper
vibration is reached. This state may usually be perceived by the sound given ont.
In some cases I arrange that the vibrator when in proper vibration shall make
contact in an electric circuit and so put into action an indicating or controlling
part. The latter may control an automatic arrangement varying the size of the
vibrating part. When the state of proper vibration is reached the frequency may
be read off on the scale.
In some cases, chiefly where the variations in the frequency are not large, I
modify the above arrangement in the following manner. Instead of one vibrating
part whose size can be varied I employ a number of vibrating parts of fixed sizes,
each one being a little smaller than those before it. These are turned so as to
respond to vibrations of certain frequencies throughout the range to be observed.
Thus a particular frequency will set one or more vibrating & will be indicated as
described above.
One of the simplest forms of the first arrangement consists of a thin strip of steel
which slides through guides closely bolding it. The free end projecting from the
guides is near an electro-magnet & its length can be varied by a rack & pinion
or a screw & nut at the other end of the strip. A pointer on the axle of the
pinion or on the screw or nut shows, with magnification, the length of the
vibrating part protruded, and thence shows the frequency on a suitably marked
scale.
In some cases I calebrate the scales by means of standard tuning-forks.
When the frequency of a periodic disturbance, which is not electrical, such as a
reciprocating motion or the rotation of a shaft, is to be measured, I connect the
moving part to a small alternator or to a commutator which makes & breaks, or
reverses, an auxiliary electric circuit, the frequency of breaking or of reversal
being equal to, or some multiple or sub-multiple of, the frequency of reciprocation
or of revolution. This auxiliary electric circuit may be led to places at any required
listance and connected to one or more electrical frequency indicators such as are

page_text: described above. This combination affords an exceedingly simple method of
indicating at distant places the speed of engines or other machinery in motion.
Dated this 17th day of June 1895.
Improvements in Apparatus for Measuring the Frequency of
Alternating or Pulsating Electric Currents, or of other Periodic
Disturbances.
I, ALBERT CAMPBELL of 15 Rothwell Street, Regent's Park, London, N.W.,
late of 34 St. George's Square, Regent's Park, London, N.W., Electrician, 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:-
If a piece of elastic material (wholly or partly magnetic, or its equivalent),
tuned to vibrate with a particular frequency, be brought near an electro-magnet
excited by a varying current, the piece will be set into vibration if the variation of
the current is such as to produce resonance. I shall designate the piece of elastic
material the "vibrator." The electro-magnet usually has a well-laminated core,
but in some cases (e.g. when large currents are employed) it may be coreless, or in
fact merely a conductor carrying the current.
More than one electro-magnet may
be used. The vibrator may be placed so as to form the core or part of the core of
an electro-magnet and magnetic material or other electro-magnet or electro-
magnets may be placed near it; or an electro-magnet with elastic leads may be
mounted on the vibrator. These conditions are applicable to most of the arrange-
ments described below, but for clearness I shall only indicate below the simplest
arrangement of vibrator.
In some cases, usually where the variations in the frequency to be measured are
not large, I employ one or more vibrators each tuned to respond to a different
frequency, indicated by a number near it. The one which vibrates most strongly
indicates by its number the approximate frequency of the current exciting the electro-
magnet or electro-magnets. This arrangement is shown in Figures 6 & 7 where
A, A, A, A are four strips of steel and B is an electro-magnet. The four parts
like that marked C will be described later on.
The magnet is not shown in most of the other figures as it occupies a position
similar to that in Figs. 6 & 7.
More commonly I employ a vibrator which can be tuned to respond to any
frequency within a given range. Two cases here arise.
Case I. when the vibrator has a free end. The vibrator may be a rod, wire,
strip, or plate. Here I effect the tuning by making the vibrator slide through a
clamp in such a way that the length of the free end can be varied until resonance
is obtained.
Case II. In this case the vibrator has neither end free. As in Case I. I vary
the size of the vibrator until resonance is obtained, but sometimes this variation is
very small. The variation of size is produced by varying the tension applied to
the vibrator; it is well known that within proper limits the strain produced is
almost exactly proportional to the stress applied; & different amounts of strain
correspond to different frequencies.
In both Case I. & Case II. we may have driving gear to produce the
variation of size & shape, and indicating gear to indicate that variation.
I will now proceed to describe the arrangements that may be used in each case.
In Figs. 1, 2, and 3 D is the vibrator consisting of a strip of steel or other
elastic magnetic material or of non-magnetic material carrying a piece of soft iron
at its end. D can slide through the clamp E. In Figure 1. the vibrator is pushed

page_text: out by hand or otherwise until it resounds properly and then the frequency is read
off directly by the position of the pointer G on the scale F which is fastened to
the vibrator.
In Fig. 2 the variation of D's length is magnified by a rack attached to D
working in a pinion H which carries a pointer over a scale as shown. The rack
may be driven by the pinion H, a milled head being attached to the axis of the
latter. Here the driving gear is part & parcel with the indicating gear.
In Fig. 3 the driving gear is a screw J working in a nut K, the readings being
taken on a divided circle L which turns with the screw.
Any of these may be modified by having the vibrator fixed to the body of the
instrument and the clamp moved by the rackwork, screw, &c. Other arrangements
may be used to magnify the relative motion of the vibrator and its mounting, such
as those well known in aneroid barometers (e.g. levers, cord on wheel, magnifying
spring, &c.). The driving mechanism may include the indicating mechanism, as in
Figs. 2 and 3, or the latter may be distinct as in Figs. 9 & 10 where there is a
separate rack and pinion for each.
Figs. 9 and 10 show the essential parts of such an instrument. In the side view
in Fig. 10 the electric circuit (including M & R) is omitted for clearness. The
back is removed in Fig. 9 and the side in Fig. 10.
R is a non-inductive resistance, M is the electro-magnet, its core of insulated
iron wires being spread out to approach the vibrator V which is free to slide
through the clamp N. The vibrator is connected by the block Q to a slider P
which runs in the guides S S and which can be moved by means of the milled
head W acting through the pinion U and the rack T. The rack X gears into a
pinion Y whose axis carries a pointer showing on the scale Z the position of the
vibrator relative to the clamp, and hence the frequency. In cases where the
pointer goes more than once round the whole scale for the range of the instrument,
an additional pinion larger than Y may be geared into X and carry a small
pointer moving over a small auxiliary scale.
In all the last named arrangements the vibrator has to be adjusted until the
proper state of resonance is attained. I use several ways of finding when this
state has been reached. The most usual way is to alter the adjustment till the
sound given out is a maximum.
Another way is to have the vibrator suitably marked by projections, holes, or
otherwise and to observe by eye or with a microscope when it attains its maximum
amplitude of vibration; or the vibrator may have a mirror attached to it by
means of which a ray of light may be thrown on a scale in the well known manner.
For the same purpose, especially in the case of lower frequencies where the note
is not so distinct, I sometimes employ an arrangement which I shall refer to as a
"rattler." This consists of a part capable of oscillating (or vibrating) which can
be adjusted so as to be set in motion by the vibrator. The motion of the rattler or
the sound produced by it (sometimes rattling or jarring) may be used to indicate
the vibration of the vibrator. Fig. 8 shows a rattler in conjunction with a strip
vibrator. a is a spring and ba milled head by which it can be turned round an
axis so as to bring the point d (weighted or otherwise) into such a position as to be
set vibrating by the vibration of V. I sometimes arrange the rattler that it shall
strike a bell or other auxiliary sounder. It may also be arranged so as to make or
break one or more contacts in an auxiliary electric circuit or circuits containing
electric bells, glow lamps, ammeters, relays, or other electric indicating apparatus.
In Fig. 8e e represent mercury cups at which contacts are made. These
auxiliary circuits, which may in some cases be in parallel with the magnet circuit
in the instrument, may actuate automatic controlling or adjusting mechanism to
regulate the frequency, speed, &c. Sometimes the making and breaking of the
auxiliary circuit or circuits is performed by contact pieces connected directly to
the vibrator. The movements of the rattler may be observed by a lens or mirror
as described above in the case of the vibrator. To lessen the length of the
vibrator required it may be weighted at the end.

page_text: Fig. 5 shows the arrangement which I employ in Case II. mentioned above. A
steel wire (or strip) f, preferably gilded, is attached at k to a spring g which may
be of various forms. The other end of the wire f is attached to a rack i gearing
into a pinion which carries a pointer k over a scale. Sometimes I attach a pointer m
at instead. The driving and indicating gears may also be separate as in former
cases and the rack and pinion arrangements may be replaced by a screw and nut or
a worm & wheel. Sometimes I introduce a bridge at n for the wire to slide
-over. p is a rattler which can be turned round an axis at q so as to come into
contact with the wire when the latter vibrates. The electro-magnet is fixed so
that one pole is near the middle of the wire.
When the frequency of a periodic disturbance which is not electrical such as a
reciprocating motion or the rotation of a shaft is to be measured, I connect to the
moving part a contact-maker or commutator which makes and breakes or reverses
an auxiliary electric circuit the frequency of breaking or of reversal being equal
to, or some multiple or sub-multiple of, the frequency of reciprocation or of
revolution. To lessen sparking a condenser may be added in the usual manner.
A small alternator may be used instead of a mere commutator.
The auxiliary electric circuit is connected to one or more electric frequency
indicators such as are described above. This combination affords means of
indicating the speed of moving machinery &c. at places distant from that
machinery.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is:
1. An arrangement consisting of one or more electro-magnets (or their equivalent),
a clamp, and a vibrator, with mechanism by which the size of the free part of the
vibrator can be varied and the frequency indicated, substantia}
as described.
2. An arrangement consisting of an electro-magnet, a wire or strip, and a spring,
with mechanism by which the size and tension of the wire or strip may be varied
and the frequency indicated, substantially as described.
3. An arrangement consisting of a number of vibrators tuned to different
definite frequencies with one or more electro-magnets and indicating arrangements
substantially as described.
4. The use in connection with instruments containing vibrators (e.g. those in
Claims 1, 2, & 3) of an auxiliary vibrating part, designated a "rattler" above, set
in motion by the primary vibrator in order to indicate or detect the state of
vibration of the latter, substantially as described.
5. The use, in connection with the arrangements in Claims 1, 2, & 3, of
auxiliary electric circuits made and broken by the primary vibrator or by the
auxiliary vibrator mentioned in Claim 4., substantially as described.
6. The use of frequency indicating apparatus as above described combined with
an electric circuit or circuits made intermittent by a contact breaker or
commutator or an alternator for the purpose of indicating speed, substantially as
described.
Dated this 17th day of March 1896.
ALBERT CAMPBELL.