IMPROVEMENTS IN APPARATUS FOR INDICATING THE SPEED OF REVOLUTION OF SHAFTS
Year: 1881

page_text: LETTERS PATENT to Philip Cardew, Lieut. in H.M. Corps of Royal Engineers,
and of Brompton Barracks, Chatham, in the County of Kent, for an
Invention of "IMPROVEMENTS IN APPARATUS FOR INDICATING THE SPEED
OF REVOLUTION OF SHAFTS."
PROVISIONAL SPECIFICATION left by the said Philip Cardew at the Office
of the Commissioners of Patents on the 7th December 1881.
PHILIP CARDEW Lieut. in H.M. Corps of Royal Engineers and of Brompton
Barracks Chatham in the County of Kent "IMPROVEMENTS IN APPARATUS FOR
INDICATING THE SPEED OF REVOLUTION OF SHAFTS."
This Invention has for its object the exact indication of the speed of revolution
of shafts of any kind at any distance or distances.
For this purpose I cause the shaft of which the speed is required to be measured
to drive a transmitter in the nature of a dynamo-machine in which the magnetic
field is maintained constant and I measuro the current generated either by
balancing with a constant known current or in other appropriate manner.
The machine I use consists of a transmitting portion and of one or more indi-
cating portions connected by the conducting wires. It requires a few voltaic cells
of suitable nature to work it.
The transmitting portion or transmitter is formed-
(a) Of a coil of fine insulated wire coiled on two bobbins like galvanometer
bobbins.
(b) Of a cylinder of boxwood or other suitable material pivotted so as to be freo
to revolve in the centro of this galvanometer coil and having grooves cut in the
direction of its axis and round its ends in which are coiled one or more sections of
insulated wire tho ends of which are brought to commutator plates insulated on
the axle of the cylinder against which metal brushes press as in dynamo-electric
machines and receive the currents generated by the revolution of the cylinder in
the centre of the fixed coils.
(c) Of a box of soft iron completely enclosing these coils except any necessary
apertures by means of which any magnetic influence from outside is cut off.
Price £1

page_text: (d) Of the means of causing the cylinder to rotate proportionally to the rate
of rotation of the shaft consisting of toothed wheels or pulleys and belts or in
cases where the speed of the shaft is sufficiently high of a steel bar forming a
prolongation of the axle of the cylinder and having a pointed pieco at the end
which impinges on the end of the rotating shaft and takes up rotation from it 5
directly.
In the case of toothed wheel or belt gearing a shaft strongly supported on the
base piece will be necessary to carry the wheel or pulley gearing with the rotating
shaft.
As the indicator will only give speeds of rotation within certain limits it will ]
be necessary where these limits may be exceeded by the rotating shaft to have
two intermediate shafts on the transmitter on which are fixed speed cones of
V shaped pulleys to take an elastic belt also a means of putting them out of
gear with the rotating shaft while the belt is changed from pair to another
of these pulleys. Or one intermediate shaft may be fixed on the base of the
transmitter and the other geared to the rotating shaft at a nearer position.
The base plate of the transmitter to have holes for bolting the machine down
securely.
The indicating portion or indicator is formed-
(a) Of a galvanometer of suitable design with the needle either vertically or
horizontally pivoted and a pointer on the face which has two stops at equal
distances from the zero point one being marked "too fast" and the other "too
slow." The galvanometer will have a powerful controlling magnet to obviate the
necessity of keeping it in the magnetic meridian. It is wound with two coils of
fine insulated wire.
(b) Of a kind of rheostat arranged round the galvanometer and its controlling
magnet in which the resistance is varied by moving an index it will be marked
to varying velocities of rotation in place of the resistance of the coils of the
rheostat.
The proper resistance of each coil will be determined by experiment in the first
instance.
The indicator described above is intended to be fixed in the position where the
exact speed of the engine is required to be known thus in the case of ships it
would be probably on the bridge.
In such a case another pattern of indicator would be required in the engine
room which would consist of a similar galvanometer but without the resistance
coils.
Or in place of the second galvanometer the index of the first one can be made
to complete the circuits of two electric bells when it presses against the stops the
bells being of different tones and placed in different positions.
Where great accuracy is not required a similar galvanometer without the
rheostat coils or stops may be employed the needle being allowed to take up
deflections to each side and the corresponding velocities being marked on the dial
face. In this case the controlling magnet will be an electro-magnet the coil being.
inserted in either the battery circuit or that of the revolving coil as may be most
convenient or instead of a magnet the needle can be kept at zero by another
galvanometer coil wound at right angles to the other two and the whole enclosed
in an iron box to guard against extraneous magnetic influences.
•
This form of indicator will be liable to inaccuracy from changes in the resistance
of the pivots and will not admit of so great a range of speed being measured
without alteration of gearing but it has the advantage that any number of
indicators can be used all shewing the speed.
The connections of the apparatus are as follows:-
-
One pole of the battery is connected to the stationary coils of the transmitter
thence to one coil of each indicator and thenco back to the other pole of the
battery.
Also one brush of the transmitter is connected to the other coils of the indicators

page_text: thence to the varying resistance in the rheostat if used and thence back to the
other brush of the transmitter.
In cases where good earth can be obtained as in an iron ship it may be used
to complete both these circuits thus only two wires in place of four will be
required.
The current from the battery is passed through the indicator coils in such a
direction as to tend to deflect the needles to "too slow" in the first two patterns
and to shew a less velocity in the third that from the revolving coil of the
transmitter so as to tend to deflect the needles to "too fast " or to shew a greater
velocity.
The method of using this instrument is as follows all connections having been
properly made:-
To ascertain the speed of the rotating shaft to be measured observe whether the
needle of the indicator is pointing to "too fast " or to "too slow" and move tho
index of the rheostat correspondingly until the needle remains at zero. For moro
minute variations than are given on the rheostat the reading of the needle on each
side of zero can be taken and the true rate reduced.
To obtain any required speed set the index to that speed the engine driver
will then notice his indicator pointing "too fast" or "too slow" and regulate the
steam accordingly.
This apparatus depends on the principle that the clectro motive force generated
in a coil of wire revolving in a constant magnetic field varies with the velocity of
rotation of the coil.
The constant magnetic field is produced by passing a current from a constant
battery through the stationary coils of the transmitter and excluding extraneous
magnetic influences.
The current produced is kept constant in value for all electro motive forces
acting by varying the resistance in the circuit of the revolving coil. The amount
of resistance interposed affords therefore a measure of the rate of revolution.
The constancy of the current is determined by causing it to balance in effect on
the indicator needles the current passing from the constant battery.
If the speed increases or diminishes the balance is destroyed and the needle
points to "too fast" or "too slow" unless the resistanco is also altered. By using
a suitable battery and coils of high resistance its current will remain constant for
considerable periods of time but if it should alter tho effect will be felt both in the
magnetic field of the transmitter and thence on the current of the revolving coil
and equally in the balancing current and these two effects will neutralize each
other in the case of the balance indicator. In the third pattern indicator the result
would be a less deflection but this is again compensated for by the feebler current
in the controlling coil taking the place of the magnet in the other indicatora.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Philip Cardew in the Great Seal Patent Office on the 7th June
1882.
PHILIP CARDEW Lieut. in H.M. Corps of Royal Engineers and of Brompton
Barracks Chatham in the County of Kent "IMPROVEMENTS IN APPARATUS FOR
INDICATING THE SPEED OF REVOLUTION OF SHAFTS."
This Invention has for its object improvements in apparatus for indicating tho
speed of revolution of shafts of any kind at any distance or distances.
My improved speed measurer consists of a transmitting portion and of one or
more indicating portions connected by conducting wires.
The purpose of the transmitting portion of the machino is to generate an electro-
motive force it should be under such conditions that the force may be proportional
to the velocity of rotation whilst the purpose of the indicating portion is to
appreciate this electro motivo force by measuring the current which it maintains
in a given circuit.
The transmitter which I consider to be the most convenient is a small magneto-
electric machine such as is represented in the annexed Drawings to a scale of one
half the actual size.
Figure 1 is a plan Figure 2 is a side elevation and Figure 3 is an end elevation
aa a are permanent horse shoc magnets which provide a constant magnetic
field b is a bobbin consisting of a cylinder of soft iron mounted upon axes or
pivots and capable of being rotated at a high velocity 500 revolutions per minute
will be suitable as a mean speed. The motion is imparted to the bobbin from the
shaft to which the indicator is required to be applied by any convenient arrange-
ment of gear. The soft iron cylinder is grooved out on the two sides to receive tho
coil of silk covered copper wire b¹ the resistance of which may conveniently be
about 100 ohms c is a commutator consisting of a cylinder of brass mounted
upon one of the pivots and divided into two parts which are insulated the one
from the other the extremities of the coil b' are attached to the two parts of the
commutator d d are springs bearing upon the commutator and serving to convey
the currents away.
ce are binding screws for making the connections with insulated wires passing
to the indicating portions of the apparatus.
The transmitter represented in the Drawings is adapted to yield continuous
currents but in some cases alternating currents are to be preferred and then the
divided cylinder c is replaced by two insulated discs with a spring & bearing
upon each.
When continuous currents are employed I make the indicating portion of the
apparatus in the form of an upright galvanometer similar to the well known
"needle telegraph" instrument. I uso a steel magnetic needle controlled or
maintained at zero by a bent magnet which clasps the galvanometer coils so that
its poles are near those of the needle. I generally employ two such indicating
galvanometers in circuit thus in the case of the application of the speed indicator
to show the rate of the engines in a steam boat one indicating galvanometer will
be provided in the engine room and the other upon the bridge In such a case and
to work with the transmitter previously described it will be suitable that the
resistance in the coils of each indicating galvanometer should be 200 ohms. The
dial is graduated with a suitable scale on either side of a zero point and this scale
is figured so that the number of revolutions of the engines per minute either ahead
or astern may be directly read off. I also provide resistance coils in the circuit for
the purpose of adjusting the total resistance until it is found that the instrument
indicates truly. This provides against errors due to changes in the magnetism of
the transmitter. Coils giving a means of interposing any resistance from 1 to 200

page_text: ohms will be suitable. Where two or more indicating galvanometers are used in
the same circuit provision may be made for shunting a few convolutions of the
coils of each so that the two galvanometers may be made to give identical
indications in case their indications are found to differ. The resistance of the
external circuit should in all cases be greater than that of the transmitter this
applies also to the other forms hereinafter described.
When it is not required to indicate the direction in which the shaft is rotating
the indicating portion of the apparatus may very conveniently take the form of a
mercurial thermometer. The bulb of the thermometer is made in the form of a
pair of horns and a platinum wire is sealed into the extremity of each horn.
If there are to be two indicating thermometers in circuit the dimensions of the
horns are such that when they are filled with mercury the resistance to an electric
current passing from one platinum wire to the other is about 50 ohms The transmitter
in this case having a resistance of 25 ohms. The thermometer is filled in the
usual way and it is graduated with a temperature scale. It is also provided with
a moveable scale for reading off directly the number of revolutions of the shaft
The zero of the scale is to be set to the temperature of the room at the time of
taking the observation. This instrument being placed in circuit with the trans-
mitter and the transmitter being in movement the mercury in the bulb becomes
heated more or less by the passage of an electric current and the height of the
mercury in the capillary tube then marks the speed or rotation upon the scale.
With this thermometric indicator I prefer to employ an alternating current
transmitter.
Another convenient form for the indicating portion of the apparatus is a
modification of the differential air thermometer. It consists of two glass bulbs
filled with air and having between them a U form tube containing liquid the
whole so arranged that when the temperature is uniform throughout the liquid
stands at the same elevation in the two limbs of the U tube. In one of the bulbs
(which I make of an elongated form) I enclose a coil of platinum wire offering a
resistance to the passage of a current. When this coil is heated by a current it
imparts the heat to the air in the bulb and expands it.
A scale is provided on which may be read the difference of level in the two
limbs of the U tube and the figures read off give directly the number of rotations
of the shaft per minute. The bulbs may advantageously be immersed in a cistern
of water to ensure that the passage of the current may be the sole cause of
difference of temperature and to diffuse the heat in a uniform manner.
The adjustment of the readings of the instrument to accord with the result
obtained directly by counting or by other controlling method is effected by
introducing more or less resistance into the circuit.
Having thus described the nature of my said Invention and the manner of
performing the same I would havo it understood that I claim,-
First My improved speed measurer consisting of a transmitting portion which
being revolved by the shaft the speed of which is required to be known generates
an electro-motive force and an indicating portion which by measuring the current
resulting from this force indicates the speed substantially as described.
Second The combination of apparatus substantially as herein described.
In witness whereof I the said Philip Cardew have hereunto set my hand and
seal this Sixth day of June in the year of our Lord One thousand eight
hundred eighty two.
P. CARDEW. (L.S.)