Improvements in Speed Indicators and like Instruments.
Year: 1894

page_text: PROVISIONAL SPECIFICATION.
Improvements in Speed Indicators and like Instruments.
1, CHARLES SPRATT, of 9 Erlanger Road New Cross Gate in the County of
Kent, Electrician, do hereby declare the nature of this invention to be as
follows:-
:-
This invention relates to instruments whose action depends on magnetic torque.
I have discovered that more accurate results are obtained by making the
armature of manganin or similar metal instead of the metals (generally_copper)
hitherto employed. My improvements also relate to lessening the effects of
friction in such instruments and to making their indicators move in the same
direction whether the driving shaft is revolving forwards or backwards.
My speed indicator is constructed in the following manner :-
Fixed upon the shaft whose speed is to be indicated is a wheel carrying on one
side a number of magnets, which are preferably poimanent horse shoe magnets.
Parallel to and co-axial with the wheel is a manganin disc having its edge
between the poles of the magnets which point radially inwards or the edge of
the disc may be turned inwards and the magnet point outwards. This disc can
revolve about its axis but in so doing winds up a helical spring one end of which
is fixed to its centre whilst the other end is fixed to the frame of the machine.
As the wheel revolves the magnets tend to carry the disc with it but it only
turns until the tendency of the magnets to rotate it is exactly balanced by the
resistance of the spring and it then remains stationary so long as the speed of
rotation of the wheel continues the same. The axis of the disc carries a hand or
pointer which evolves over a properly graduated scale showing the speed of rotation
of the wheel by the angle through which the disc has tuned.
Two helical springs are preferably employed, and then ends are secured to the
disc by being simply passed through slots in two pins fixed on the same face near
to and one on either side of its centre or the ends of the springs may be fixed to a
square nut fiee to move along the square end of the axle.
By this means a very steady action is obtained and the leading of the instrument
18 little affected by changes of temperature as any expansion or contraction of the
springs only causes their ends to move longitudinally.
In order to lessen the effect of friction on the motion of the disc I form the
bearing for one end of its spindle in the shaft or wheel so that this bearing rotates
whilst the other is fixed. The friction of one beating therefore tends to accelerato
the motion of the disc and that of the other to retard it, these tendencies more or
less counteracting each other.
When it is desired to indicate the speed of the driving shaft when reversed the
following device is adopted :-The wheel cari ying the magnets is not mounted upon
the driving shaft but on a separate shaft at whose end is fixed a bevel pinion
gearing with one or other of two bevel wheels fixed on a sleeve on the driving
shaft. This sleeve has a diagonal slot in it which receives a pin fixed to the shaft.
When the driving shaft is moving in one direction the pin is at one end of the slot
and the corresponding bevel wheel is in gear but when the motion is reversed the
pin travels to the other end of the slot and the incline of the latter causes the
sleeve to move longitudinally on the shaft throwing the first mentioned bevel wheel

page_text: out of gear and putting the other in so that the magnets are always driven in the
same direction. A light spring is provided bearing against the sleeve to prevent
its being turned by friction when the pin is travelling in the slot.
Dated this 22nd day of December 1894.
Improvements in Speed Indicators and like Instruments.
1, CHARLES SPRATT, of 9 Erlanger Road, New Cross Gate, in the County of
Kent, 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.―
'This invention relates to instruments whose action depends on magnetic torque,
such as speed indicators, ships logs, anemometers, trocheameters or any other
apparatus for the purpose of indicating the speed of revolution of any rotating
body.
I have discovered that more accurate results are obtained by making the
armature of manganın or similar metal instead of the metals (generally copper)
hitherto employed. My improvements also relate to lessening the effects of
friction in such instruments and to making their indicators move in the same
direction whether the driving shaft is revolving forwards or backwards.
My speed indicator is constructed in the following manner :-
Fixed upon the shaft whose speed is to be indicated is a wheel carrying on one
side a number of magnets, which are preferably permanent boise shoe magnets.
Parallel to and co-axial with the wheel is a manganin disc having its edge between
the poles of the magnets which point radially inwards or the edge of the disc may
be turned awards and the maguet point outwards This disc can revolve about
its axis but in so doing winds up a helical spring one end of which 18 fixed to its
centre whilst the other end is fixed to the frame of the machine.
As the wheel revolves the inagnets tend to carry the disc with it but it only
turos until the tendency of the magnets to rotate it is exactly balanced by the
resistance of the sping and it then remains stationary so long as the speed of
1otation of the wheel continues the same. The axis of the disc cuires a hand or
pointer which revolves over a properly graduated scale showing the speed of
rotation of the wheel by the angle through which the disc has turned.
Two helical springs are preferably employed and their ends are secured to the
disc by being simply passed through slots in two pins fixed on the saine face near
to and one on either side of its centre or the ends of the springs may be fixed to
a square nut free to move along the square end of the axle.
By this means a very steady action is obtained and the reading of the instrument
is little affected by changes of temperature as any expansion or contraction of the
springs only causes their ends to move longitudinally.
In order to lessen the effect of friction on the motion of the disc form the
bearing for one end of its spindle in the shaft or wheel so that this bearing rotates
whilst the other is fixed. The friction of one bearing therefore tends to accelerate
the motion of the disc and that of the other to retard it, these tendencies more or
less counteracting each other.
When it is desired to indicate the speed of the driving shaft when reversed the
following device is adopted -The wheel carrying the magnets is not mounted upon
the diving shaft but on a separate shaft at whose end is fixed a bevel pinion gearing
with one or other of two bevel wheels fixed on a sleeve on the diving shaft. This

page_text: '
sleeve has a diagonal slot in it which receives a piu fixed to the shaft. When the
diving shaft is moving in one dnection the pin is at one end of the slot and the
quesponding bevel wheel is in gear but when the motion is reversed the pin
tiavels to the ether end of the slot and the incline of the latter causes the sleeve
to move longitudinally on the shaft throwing the first mentioned bevel wheel out
of gen and putting the other in so that the magnets are always duiven in the same
direction. A light spring is provided bearing against the sleeve to prevent its
being turned by friction when the più is travelling in the slot.
Figure 2 is a transverse section on the line X X Figure 1, and
Figme 3 is a plan of the night hand end of Figure 1.
Figmic 4 is a sectional, Figure 5 a left hand, and Figure 6 a right hand side
levation of a detail
a is the driving pulley, and a' its shaft, to which the piu a is fixed. This pin
works in an inclined slot in the sleeve b whose ends cairy bevilled pinions & bone
or other of which gears with the pinion c on the shaft c¹.
d are springs (omitted in Figure 3) carrying function pads bearing on the
sleeve, these prevent the sleeve b from being carried 1ound merely by the friction
of the shaft a' and ensure the pin a' by its action on the ucline putting one o
other of the pinious & into gear with the pinion e The shaft c carries a wheel e
to which are fixed horse-shoe magnets et preferably arranged as shown so that
they alternately have their north and south poles next to the wheel. f is a disc of
manganın (an alloy of 84 per cent. copper, 12 per cent. manganese, and 4 per cent.
mickel being suitable). It is an advantage when constructing a low speed instru-
ment to coat the manganın disc with a thin deposit of copper as it gives greater
magnetic torque and the temperature change only effects it slightly to what it does
a solid copper disc. The disc is mounted on the shaft which carries a hand
ot pointer and works in bearings g g'. The bearing g is fixed to the frame of
the instrument and the bearing to the shaft c¹ hhare two spiral springs each
having one end fixed to the shaft 1 by being clipped between it and a plate
secured by a screw whilst then other ends are fixed to the bracket on the
fiame of the instrument by the screws ³.
The effective length of the spingh can be adjusted by a regulator similar to
that of a clock, it consists of an aim (Figures 1, 4 and 0) split at its end to
embrace the spring and mounted on a plate which can be turned by a pin
projecting through a slot in the dial. is a sping arm against which the
band strikes when it comes to the zero point.
lu place of the springs above described helical springs may be employed,
as shown at Figures 7 & 8. Oue end of each is fixed to the fra.ne whilst the
other ends are passed through slots in two pins on the disc as shown in
Figure 7 or to a square out m on the end of the shaft f' which is squared to
receive it as shown in Figure 8.
Having now particularly described and ascertained the nature of my said inven-
tion and in what maunci the same 18 to be performed 1 declare that what I
claim 18:
1. Speed indicators and like instruments whose action depends on magnetic
torque having an armature of manganın or similar metal.
2. The method substantially as described of lessening the effects of fiction in
speed indicators and like insti uments.
3. The arrangement for making the indicator move in the same direction whether

page_text: the driving shaft is revolving forwards or backwards substantially as described
and shown at Figure 3.
4. Speed indicators and like instruments substantially as described and shown
anfthe drawings.
Dated this 11th day of September 1895.
CHARLES SPRATT.