New or Improved Device for Indicating the Frequency of an Electric Current or Currents, the said Device being applicable for Signalling and Indicating Speeds and the like.
Year: 1898

page_text: Date of Application, 17th Dec., 1898
Complete Specification Left, 18th Sept., 1899-Accepted, 17th Dec., 1899
PROVISIONAL SPECIFICATION.
New or Improved Device for Indicating the Frequency of an Electric
Current or Currents, the said Device being applicable for
Signalling and Indicating Speeds and the like.
I, WILLIAM ERNEST BURNAND, of Club Gardens Walk, Highfield, Sheffield, in
the County of York, Electrical Engineer, do hereby declare the nature of this
invention to be as follows:-
It is well known that if two circuits containing different amounts of self
induction or capacity are connected in parallel to a source of pulsating currents
of electricity, the ratio of the currents in the two circuits will vary with the
frequency of the source of supply even though the tension at their common ter-
minal remains unaltered.
Thus if one circuit, say A, has very little self induction, while the other, say B,
has considerable self induction, the current in A will scarcely alter with a change
in the frequency, while the current in B will increase with diminished frequency
and decrease with increased frequency, the tension meanwhile remaining the
same.
I have invented an instrument whose action is based on this fact for measuring
the frequency of a pulsating current and derivatively for signalling and indi-
cating speeds and the like. For this purpose I arrange the two circuits in such
a way that the currents passing through them exert a magnetic action upon a
movable system whose position thus depends on the frequency.
I shall now proceed to describe one way in which I may carry my invention
into effect, though I do not limit myself to the particular arrangement herein-
after described.
I wind the two circuits in the form of two coils. I arrange that the one
circuit, say A, shall have only as much self induction as is necessarily present in
the coil itself, and I insert into the other circuit say B, an inductive resistance,
with an iron core, having considerable self induction.
I arrange that two cores of iron wire or of other suitable construction, hang
down inside the two coils, which may be placed in a vertical position, and I
suspend the cores from a beam which may be made to swing about a fixed pivot.
I attach to the beam a pointer which indicates on a scale the position of the
beam, which I may adjust by means of weights or any other suitable device.
The action is as follows: When the two circuits are connected in parallel to the
source of electricity, a current passes in each circuit whose strength depends on
the tension and the frequency of the source, and on the resistance and self induc-
tion of the circuit. The currents act upon the two cores, setting the movable
system in a definite position. As long as the frequency and the tension are
unaltered, the currents in the two circuits remain the same. If however the
tension remains the same but the frequency increases, the current in both circuits
will be reduced, but that in B to a much greater extent than that in A. The
result is that the movable system is tilted over and the pointer takes up a new
position corresponding to the increased frequency. I sometimes make the two
Coils act upon a beam of polarised light whose angular deflection is an indication

page_text: of the frequency, or I may make them act upon a mirror that reflects a beam
of light.
Although I have here described one way of carrying out my invention, in
which I use two coils with two separate cores, I desire it to be understood that
I do not confine myself to this particular arrangement but may for instance
employ two coils so set as to act upon a single core.
I also desire it to be understood that while I have in describing one form of
my invention, spoken of the different amounts of self-induction in the two circuits
I may also make use of two circuits which have different degrees of capacity.
In carrying out my invention I use means whereby I ensure that a change in
the tension of the source of supply shall have no influence on the indicator.
For this purpose I may for instance, construct the iron core of the inductive
resistance in two parts, with an air gap between them, so that the variation of
the back tension of self induction is proportional to that of the source of supply
Thus when the latter alters in amount, the current in both circuits increases in
the same proportion, and the indicator is not effected. Or I may for the same
purpose introduce into the circuit A a coil with small self induction with closed
or nearly closed magnetic circuit with iron magnetised nearly to saturation.
The indicator may be connected to a generator producing current for lighting
or other purposes, whose frequency has to be measured. When it is desired to
show at a distance the speed of a shaft or other rotating part, a generator may
be specially constructed, and driven by the shaft in any suitable manner, or I
may mount part of the generator on the shaft, the other part being stationary.
:
may, for instance, mount a disc on the shaft, carrying a number of soft iron
armatures which, as they rotate, pass between the poles of a fixed magnet. A
coil may be wound on the magnet, and connected to the frequency indicator. As
each armature comes between the poles of the magnet, a tension is induced in the
coil, and a current made to pass through the indicator, whose frequency, as
shown on the indicator, is a measure of the speed of the shaft.
The scale may be graduated by experiment and made to read directly in periods
per second or in other convenient unit. In cases where it is desired to use the
indicator for the purpose of sending signals, I arrange to vary the frequency by
any convenient method at the transmitting end, as for instance by using an
induction coil and varying the length of the active portion of the contact spring.
the variation of frequency being shown on the indicator, and serving as a means
of communication.
In using the term "pulsating" I desire it to be understood that I may use any
form of varying current, whether undulating alternating, intermittent or other
wise.
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COMPLETE SPECIFICATION (AMENDED).
New or Improved Device for Indicating the Frequency of an Electric
Current or Currents, the said Device being applicable for
Signalling and Indicating Speeds and the like.
I, WILLIAM ERNEST BURNAND, of Club Gardens Walk, Highfield, Sheffield, in
the County of York, Electrical Engineer, 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.
It is well known that if two circuits containing different amounts of self induc-

page_text: tion or capacity are connected in parallel to a source of pulsating currents of
electricity, the ratio of the currents in the two circuits will vary with the frequency
of the source of supply even though the tension at their common terminal remains
unaltered.
Thus if one circuit, say A, has very little self induction, while the other, say B,
has considerable self induction, the current in A will scarcely alter with a change
in the frequency, while the current in B will increase with diminished frequency
and decrease with increased frequency, the tension meanwhile remaining the same.
I have invented an instrument whose action is based on this fact for measuring
the frequency of a pulsating current and derivatively for signalling and indicat-
ing speeds and the like. For this purpose I arrange the two circuits in such a
way that the currents passing through them exert a magnetic action upon a
movable system whose position thus depends on the frequency.
I shall now proceed to describe one way in which I may carry my invention
into effect, and for that purpose I shall refer to Figure I of the accompanying
drawings.
I wind parts of the two circuits A and B in the form of two coils, 1 and 2. I
arrange that the one circuit, say A, shall have only as much self induction as is
necessarily present in the coil itself, and I insert into the other circuit, say B, an
inductive resistance 3, with an iron core 4, having considerable self induction.
I arrange that two cores, 5 and 6, of iron wire or of other suitable construc-
tion, hang down inside the two coils, 1 and 2, which may be placed in a vertical
position, and I suspend the cores from a beam, 7, which may be made to swing
about a fixed pivot, 8. I aftach to the beam a pointer, 9, which indicates on a
scale the position of the beam, which I may adjust by means of weights or any
other suitable device.
The action is as follows: When the two circuits are connected in parallel to
the source of electricity, a current passes in each circuit whose strength depends
on the tension and the frequency of the source, and on the resistance and self
induction of the circuit. The currents act upon the two cores, setting the movable
system in a definite position. As long as the frequency and the tension are
unaltered, the currents in the two circuits remain the same. If, however, the
tension remains the same but the frequency increases, the current in both circuits
will be reduced, but that in B to a much greater extent than that in A. The
result is that the movable system is tilted over and the pointer takes up a new
position corresponding to the increased frequency.
To ensure that a change in the tension of the source of supply shall not influence
the indicator I construct the iron core of the inductive resistance in two parts, 10,
11, with an air gap, 12, between them, so that the variation of the back tension
of self induction is proportional to that of the source of supply. Thus, when the
latter alters in amount, the current in both circuits increases in the same pro-
portion, and the indicator is not affected. Or I may for the same purpose intro-
duce into the circuit A à coil with small self induction with a closed or nearly
closed magnetic circuit with iron magnetised nearly to saturation.
I sometimes make the two coils act upon a beam of polarised light whose
angular deflection is an indication of the frequency, or I may make them act
upon a mirror that reflects a beam of light.
In Figure II, I show a practical form of my indicator. This differs from
the diagram (Figure 1) mainly in that the beam is dispensed with and that
the coils 1, 2 are placed in alignment, so that instead of having two separate
cores 5 and 6, one for each coil, I use a single armature 13 conveniently made
of the shape shown. 14 is the scale over which the pointer 9 ranges, and 15
and 16 are the terminals for connection with the external circuit.
This construction enables the instrument to be used with currents of wide
variation of frequency and electromotive force. If the instrument be made up
strictly as represented in Figure I the indicator would only be unaffected by
changes in electromotive force when the ampère turns in the two coils were equal,

page_text: DEVICE FOR Imarcating the Frequency of an Licctric Current OT CUTTERS, 100.
so that its range of working would be comparatively limited on a circuit subject
to wide variations of electromotive force.
The indicator may be connected to a generator producing current for lighting
or other purposes, whose frequency has to be measured. When it is desired to
show at a distance the speed of a shaft or other rotating part, a generator may
be specially constructed, and driven by a shaft in any suitable manner, or I may
mount part of the generator on the shaft, the other part being stationary.
I may, for instance, mount a disc on the shaft, carrying a number of soft iron
armatures which, as they rotate, pass between the poles of a fixed magnet. A
coil may be wound on the magnet, and connected to the frequency indicator. As
each armature comes between the poles of the magnet, a tension is induced in the
coil, and a current made to pass through the indicator, whose frequency, as
shown on the indicator, is a measure of the speed of the shaft. Any convenient
form of generator, however, which yields pulsating currents will answer my
purpose.
The scale may be graduated by experiment and made to read directly in periods
per second or in other convenient unit.
In cases where it is desired to use the indicator for the purpose of sending
signals, I arrange to vary the frequency by any convenient method at the trans-
mitting end, as for instance by using an induction coil and varying the length
of the active portion of the contact spring, the variations of frequency being
shown on the indicator, and serving as a means of communication. Such an
arrangement is diagrammatically represented in Figure III in which two stations
(transmitting and receiving) are represented at C and D. 17 and 18 are the
indicators, one at each station, connected in parallel to the circuit as shown, and
the said circuit including the secondaries of the induction coils 19 and 20. The
vibrator 21 of each coil is so constructed that the length of the active portion of
the contact spring may be altered so as to give rise to currents of different
frequencies which being read on the indicators may serve as a means of commu-
nication. When used for telegraphing I prefer, instead of employing a pointer
traversing a scale, to attach a disc to the movable part of the indicator marking
the said disc with characters which may be brought opposite the windows 22 of
the indicators. Such substitution of a disc for a pointer is well known in indica-
tors generally.
In using the term "pulsating" I desire it to be understood that I may use
any form of varying current, whether undulating, alternating, intermittent or
otherwise.
I am aware of the American Patent No. 383670, dated 29th May 1888, granted
to Oliver B. Shallenberger. In view of certain surface resemblances 1 desire it
to be understood that I do not claim anything contained in the specification
accompanying the suid patent of Shallenberger.
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 new or improved device for indicating the frequency of an electric
current or currents, substantially as set forth.
2. The means for indicating speeds substantially as set forth.
3. The means for signalling substantially as set forth.
4. In a device for the purposes specified the employment of a divided magnetic
core with intermediate gap substantially as set forth.
Dated this 14th day of September 1899.