Improvements in Electrical Measuring and Recording Instruments.
Year: 1894

page_text: Date of Application, 6th July. 1394
Complete Specification Left, 6th May, 1895-Accepted, 15th June, 1895
PROVISIONAL SPECIFICATION.
Improvements in Electrical Measuring and Recording Instruments.
I, HAYDN THIES HARRISON, of Trafalgar House, Great Newport Street, in the
County of London, Electrical Engineer, do hereby declare the nature of this
invention to be as follows:-
This invention relates inter alia to that class of electrical instruments which
records the variation of current or pressure in an electrical circuit by means of a
pen moving over a properly divided chart or paper which is moved longi-
tudinally beneath it at a constant speed by means of clockwork or other suitable
mechanism.
In this class of instruments it is necessary, in order that the friction of the pen
on the paper shall not affect the accuracy of the record, that considerable force
should be used to actuate the pen. Hitherto this object has not been obtained
without absorbing a considerable amount of electrical energy, or using in the
construction of the instrument, large quantities of iron which introduce large
errors, due to hysteresis, and my invention is designed to obviate these
disadvantages.
For this purpose in electrical measuring and recording instruments according to
one part of this invention, the coil through which the current to be measured
passes, is formed at its central portion with a slot or opening forming a hollow core
that is long and wide but shallow, and within this slot or opening works a movable
armature consisting of a thin strip or fine rod of iron that is connected by suitable
means, such as two arms arranged at the ends of the coil, to a spindle (that is
mounted to turn about an axis parallel to the said slot or opening) that operates the
arm or pointer carrying the recording pen. Within the slot or opening and at one
side thereof, so as to be parallel with the armature, is fixed a strip or bar of iron
from which there extends towards the other side of the slot or opening, a piece of
sheet iron that is made of gradually decreasing width or wedge shape from the
fixed strip or bar to the other side of the opening in the coil where its width may
be about three-fourths of the width at its widest part. This piece of sheet iron
serves to increase the distance of repulsion of the armature. A weight, spring or,
equivalent device serves to hold the armature in proximity to the fixed iron strip
or bar when no current is passing through the coil.
The arrangement is such that when a current passes through the coil the lines of
magnetic force thereby produced will be concentrated within the aforesaid slot or
opening with the result that the armature will be repelled against the action of the
weight or spring, by the fixed iron strip or bar which will be of the same polarity
as the armature. As the current increases the armature will be still farther
repelled as it tends to move along the wedge-shaped piece of iron to the narrowest
end thereof, and when the current decreases the armature will be moved in the
reverse direction by the action of the weight or spring. The armature being
connected with the recording pen the latter will be deflected with it and so caused
to register the increase or decrease of current on the moving chart with which the
apparatus is provided.
It will be obvious that with the arrangement described, the force transmitted to
the pen will be considerable as, owing to the arms supporting the armature being
of considerable length, and the hollow centre or core of the bobbin permitting the
armature to be repelled a comparatively long distance, there is a large leverage on

page_text: the spindle and a large weight or powerful spring can be used to counteract the
magnetic force. At the same time a small amount only of iron is required, as the
movable and fixed pieces of iron are always in close proximity to each other and
the lines of force are concentrated along the line of movement.
In instruments for recording variation of current in a circnit the coil is made of
thick wire, whilst on the other hand it will be obvious that if the coil be composel
of fine wire, the instrument can be used to record variations in electrical pressure.
It will also be obvious that if the pen is replaced by a pointer and a scale is
fixed underneath it, the instrument can be used as a direct reading ammeter or
voltmeter.
For recording the variations in voltage on a direct current circuit where the
pressure only varies between certain limits I provide an instrument comprising a
soft iron magnet wound with a large number of turns of fine wire and between the
two poles of which is fixed a soft iron cylinder with its periphery towards the poles
the inner faces of which are correspondingly curved. Between the cylinder and
the poles of the magnet a clearance space is left in which a fine wire coil is mounted
to freely turn through a certain angle about the axis of the cylinder as a centre.
This coil is fixed to a spindle to which the recording arm and counterweight or
spring are connected and which passes through a clearance hole in the centre of
the cylinder. The coils on the magnet and the moving coil are connected in series,
and the current is or may advantageously be conveyed to the moving coil by means
of fine strips of metal foil made of considerable length and bent into a zig-zag form
so as not to affect the free movement of the coil. The arrangement is such that
when the current flowing round the electro-magnet rises to a certain strength, the
iron will have arrived at the point of magnetic saturation. Beyond that point the
lines of force will increase slowly and the error due to hysteresis will be negligable,
but the moving coil will still tend to move round the iron cylinder as the current
flowing through it increases. This is made the working scale of the instrument,
and the magnet being highly magnetized, the torque given to the moving coil will
be very considerable. Thus if the instrument be required to record accurately
between seventy and one hundred and twenty volts, the electro-magnet is wound.so
that it will become saturated at seventy volts, and the counterweight or spring is
adjusted so that the instrument will start to record at that point and will record
very accurately above that point. By replacing the pen by a pointer, and the moving
chart by a scale, this instrument can be used as a direct reading voltmeter.
Dated this 6th day of July 1894
Potical measuring and Recording instruments.
J, HAYDN THIES HARRISON, of Trafalgar House, Great Newport Street, in
the County of London, 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 :-
This invention relates inter alia to that class of electrical instruments which
records the variation of current or pressure in an electrical circuit by means
of a pen moving over a properly divided chart or paper which is moved longitudinally
beneath it at a constant speed by means of clockwork or other suitable
mechanism.
In this class of instruments it is necessary, in order that the friction of the pen

page_text: on the paper shall not affect the accuracy of the record, that considerable force
should be used to actuate the pen.
Hitherto this object has not been obtained
without absorbing a considerable amount of electrical energy, or using in the
construction of the instrument, large quantities of iron which introduce large
errors, due to hysteresis and my invention is designed to obviate these dis-
advantages as I will now proceed to explain by reference to the accompanying
illustrative drawings wherein
Fig. 1 is a side elevation, with part of the recording arm or pointer removed,
and Fig. 2 an end elevation, showing an electrical measuring and recording
instrument constructed according to one part of this invention.
Fig. 3 is an inverted horizontal section on the line of Fig. 1.
1 is the coil through which the current to be measured passes.
It is formed at
its central portion with a slot or opening 2 forming a hollow core that is long and
wide but shallow as shown and within which works a movable armature 3 consisting
of a thin strip, or it may be a fine rod, of iron that is connected by suitable means,
such as two arms 4, arranged at the ends of the coil, to a spindle 5 which is
mounted to turn about an axis parallel to the said slot or opening and operates the
arm or pointer 6 carrying the recording pen 7. The coil with its bottom 8 is
carried by a frame 9 which is adapted to be secured to a vertical board or support
and carries a bracket 9" in which the spindle 5 is pivoted. Within the slot or
opening 2 and at one side thereof, so as to be parallel with the armature, is fixed
by means of a bar 10 of non-magnetic material, a strip or a bar 11 of iron,
composed preferably of laminated sheet iron, from which there extends towards
the other side of the slot or opening, a piece 11* of sheet iron that is made of
gradually decreasing width or wedge shape from the fixed strip or bar to the other
side of the opening in the coil where its width may be about three fourths of the
width at its widest part as shown in Fig. 3. In cases where the controlling force
does not increase rapidly the wedge shaped piece of iron may be dispensed with.
This piece of sheet iron serves to increase the distance of repulsion of the
armature 3. A weight 12 fixed by a rod 12* to the spindle 5, or it may be spring
or equivalent device, serves to hold the armature 3 in proximity to the fixed iron
strip or bar 11 when no current is passing through the coil.
As will be seen, the arrangement is such that when a current passes through
the coil 1, the lines of magnetic force thereby produced will be concentrated
within the slot or opening 2 with the result that the armature 3 will be repelled
against the action of the weight 12, or its equivalent, by the fixed iron strip or
bar 11 which will be of the same polarity as the armature. As the current
increases, the armature will be still further repelled as it tends to move along the
wedge-shaped piece of iron 11 to the narrowest end thereof, and when the current
decreases, the armature will be moved in the reverse direction by the action of
the weight 12, or its equivalent. The armature being connected as hereinbefore
described with the recording pen 7, the latter will be deflected with it and so
caused to register the increase or decrease of current on a moving chart carried by
a clockwork actuated drum 13 with which the apparatus is provided and which
may be mounted to rotate between a pair of plates 14 carried by rods 14ª pivoted
to the frame 9 at 14b. By this means of supporting the recording drum a very
simple adjustment of the pressure of the recording peu upon the chart paper is
obtained which also has the advantage that the pressure can be adjusted while the
instrument is recording, without affecting the record as the moving parts do not
require to be touched.
It will be obvious that with the arrangement described, the force transmitted to
the pen will be considerable, as, owing to the arms 4 supporting the armature being
of considerable length, and the hollow centre or core of the bobbin 8 permitting
the armature to be repelled a comparatively long distance, there is a large leverage
on the spindle 5, and a comparatively large weight 12, or powerful spring, can be
used to counteract the maguetic force. At the same time a small amount only of
iron is required, as the movable and fixed pieces of iron 3 and 11 11* respectively.

page_text: are always in close proximity to each other and the lines of force are concentrated
along the line of movement.
In instruments for recording variation of current in a circuit, the coil 1 is made
of thick wire as shown, whilst on the other hand it will be obvious that if the coil
he composed of fine wire, the instrument can be used to record variations in
electrical pressure. It will also be obvious that if the pen 7 is replaced by a
pointer, and a scale is fixed underneath it, the instrument can be used as a direct
reading ammeter or voltmeter.
The instrument herein before described can be used for alternating or direct
currents.
For recording the variations in voltage on a direct current circuit where the
pressure only varies between certain limits, I provide an instrument of the kind
shown in Figs. 4 and 5, which are elevations at right angles to each other, and in
Fig. 6, which is a section on the lines y y of Fig. 5.
This instrument comprises a soft iron magnet the core 15 of which is wound
with a large number of turns of fine wire 16 and between the two poles 15°, of
which is fixed, by means of a non-magnetic plate 17 secured to the said poles, a
soft iron cylinder 18 (Fig. 6) having its periphery towards the poles, the inner
faces of which are correspondingly curved. Between the cylinder and the poles
of the magnet, a clearance space 19 is left in which a fine wire coil 20), carried by
a bobbin 21, is mounted to freely turn through a small angle about the axis of the
cylinder 18 as a centre. This coil is fixed to a spindle 5 to which the recording
arm 6 and counterweight 12, or spring, are connected and which passes through a
clearance hole in the centre of the cylinder. The coils 16 on the magnet core 15
and the moving coil 20 are connected in series, and the current is or may
advantageously he conveyed to the moving coil by means of fine strips 22 of metal
foil, made of considerable length, and bent into a zig-zag form as shown so as not
to affect the free movement of the coil 20, these strips being connected to insulated
sleeves 23 carried by the spindle 5 and connected with the said coil.
As will be seen, the arrangement is such that when the current flowing round
the electro-magnet coils 16 rises to a certain strength, the iron will have arrived
at the point of magnetic saturation. Beyond that point the lines of force will
increase slowly, and the error due to hysteresis will be negligable, but the moving
coil 20 will still tend to move round the iron cylinder 17 as the current flowing
through it increases. This is made the working scale of the instrument, and the
magnet core 15 being highly magnetized, the torque given to the said moving coil
will be very considerable. Thus if the instrument be required to record accurately
between seventy and one hundred and twenty volts, the electro-magnet is wound
so that it will become saturated at seventy volts, and the counter-weight 12, or
spring, is adjusted so that the instrument will start to record at that point, and will
record very accurately above that point. By replacing the pen 7 by a pointer,
and the moving chart on the drum 13, by a fixed scale, this instrument can be used
as a direct reading voltmeter.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manuer the same is to be performed I declare that what I
laim is :-
1. An electrical measuring or measuring and recording instrument comprising a
pointer or an arm adapted to carry a recording pen or marker fixed on a spindle,
and provided outside the coil with a counter-weight or its equivalent an armature
connected to the said pointer or arm, and located within a long wide shallow slot
or opening in a coil through which the current to be measured can be caused to
pass, and within the said slot a fixed device of iron against which the pointer or
arm is kept by the weight or its equivalent when no current is passing through
the coil but by which iron device the armature is repelled when a current is passing
through the coil thereby deflecting the 'pointer or arm substantially as herein
described.

page_text: 2. An electrical measuring or measuring and recording instrument of the kind
specified in the preceding claim in which the iron device is in the form of a strip
or bar fixed at one side of the slot or opening in the coil and parallel with the
armature and is provided with a wedge shaped extension adapted to increase the
distance of repulsion of the armature, substantially as herein described.
3. For measuring or measuring and recording variations in voltage between
definite limits in an electric circuit, an instrument in which the arm carrying the
recording pen or marker, or a pointer is moved against the action of a weight or
its equivalent by a fine wire coil mounted to turn in a magnetic field formed
between a soft iron cylinder and the two poles of a soft iron magnet core wound
with a large number of turns of fine wire, the arrangement being such that the
said coil and arm or pointer will not commence to record until the voltage attains
the minimum limit, at which time the magnet core will be magnetised to saturation,
substantially as herein described for the purpose specified.
4. The improved electrical measuring or recording instrument hereinbefore
described with reference to and shown in Figs. 1, 2 and 3 of the drawings annexed,
or modified as set forth.
5. The improved electrical measuring or recording instrument hereinbefore
described with reference to and shown in Figs. 4, 5, and 6 of the drawings annexed,
or modified as set forth.
Dated this oth day of May 1895.
For the Applicant,
W. LLOYD WISE,
46, Lincoln's Inn Fields, London, W.C., Chartered Patent Agent.