IMPROVEMENTS IN ELECTRIC MEASURING INSTRUMENTS to be as follows:
Year: 1885

page_text: I, JOHN GRICE STATTER of Middleton Road Works, Dalston, in the county of
Middlesex, Electrical Engineer do hereby declare the nature of the said invention
for "IMPROVEMENTS IN ELECTRIC MEASURING INSTRUMENTS to be as follows:-
"
My invention relates to improvements in electric measuring instruments my
object being to obtain an instrument which shall be free from excessive inequality
of scale division and liability to change caused by alterations in terrestrial mag-
netism or the strength of springs, and which shall be practically free from the
errors due to the influence of residual magnetism.
If a soft iron needle capable of rotation about an axis at a right angle to its
length and which is not vertical be placed within a coil or loop of iron carrying
an electric current it will experience a force tending to keep its magnetic axis
at right angles to the plane of such coil or loop. If this tendency on the part of
the needle be resisted by the force of gravitation acting upon a small weight
attached to the aforesaid needle the needle will take up positions dependent upon
the strength of the current passing in the coil and such positions as is well
known may be used to indicate the strength of the current passing at that
moment, but the alterations or variations in position produced by the same
increment of current give very unequal divisions in different parts of the scale.
The object of my invention is to obtain more nearly equal division and at the
same time to increase the total available range.
For this purpose I take such a coil and place within it a laminated soft iron
needle of very small mass in such a position that it is not only acted upon by
the coil in the manner hereinabove described but experiences a force tending to
draw it to the centre of the coil with respect to its length after the well known
manner in which a solenoid acts upon its core; and the needle is placed in such
a position with respect to its axis of rotation that this force acts in conjunction
with the hereinabove described turning force and supplements it, its movement
increasing when that of the turning force is diminishing, and it is by the com-
bination of this force with the turning force that I obtain a much more even scale
and a greater available range; the exciting power of the coil is sufficient to
saturate magnetically the very small mass of iron in the needle at the lowest
current for which the instrument is designed to measure and the opposing forces
which determine the position of the needle are sufficiently great to render the
deflecting effect of terrestrial magnetism inappreciable,

page_text: The deflecting coil may be wound either with a few turns of thick wire or
many turns of fine wire according as it is desired to measure current or electro
motive force as well known.
In instruments used to measure electromotive force resistances composed of fine
filaments of carbon embedded in plaster of Paris, asbestos paste or other suitable
cementing material may be placed in series with the coil.
A level or plummet or other suitable arrangement and levelling screws or other
means of adjustment are provided to ensure the instrument being always set up in
the same position with regard to the vertical; or the instrument may be suspended
by gimbals.
It will be obvious that my improved electric measuring instrument can be used
to measure either direct or alternating currents.
G. F. REDFERN,
Agent for the Applicant.

page_text: Improvements in Electric Measuring Instruments.
I JOHN GRICE STATTER, of Middleton Road Works, Dalston, in the county of
Middlesex, 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:-
My invention relates to improvements in electric measuring instruments, my
object being to obtain an instrument which shall be free from excessive inequality
of scale division and liability to change caused by alterations in terrestrial mag-
netism or the strength of springs and which shall be practically free from the errors,
due to the influence of residual magnetism.
If a soft iron needle capable of rotation about an axis at a right angle to its
length and which is not vertical be placed within a coil or loop of wire carrying
an electric current it will experience a force hereinafter called the turning force
tending to keep its magnetic axis at right angles to the plane of such coil or loop.
If this tendency on the part of the needle be resisted by the force of gravitation
acting upon a small weight attached to the aforesaid needle the needle will take
up positions dependent upon the strength of the current passing in the coil and
such positions as is well known may be used to indicate the strength of the current
passing at that moment, but the alterations or variations in position produced by
the same increment of current give very unequal divisions in different parts of
the scale.
The object of my invention is to obtain more nearly equal divisions and at the
same time to increase the total available range.
For this purpose I take such a coil and place within it a laminated soft iron
needle of very small mass in such a position that it is not only acted upon by
the coil in the manner hereinbefore described but experiences a force tending to
draw it to the centre of the coil with respect to its length after the well known
manner in which a solenoid acts upon its core and hereinafter called the
solenoidal force; and the needle is placed in such a position with respect to its
axis of rotation hereinafter called the axis, that this force acts in conjunction with
the hereinbefore described turning force and supplements it, its moment increasing
when that of the turning force is diminishing, and it is by the combination of this
force with the turning force that I obtain a much more even scale and a greater
available range; the magnetising or exciting power of the coil is sufficient to
saturate magnetically the very small mass of iron in the needle at the lowest
current for which the instrument is designed to measure and the opposing forces.
which determine the position of the needle are sufficiently great to render any
deflecting effect of terrestrial magnetism inappreciable.
The deflecting coil may be wound either with a few turns of thick wire or many
turns of fine wire according as it is desired to measure current or electro motive
force as is well known.
In instruments used to measure electro motive force resistances composed of fine
filaments of carbon embedded in plaster of Paris, asbestos-paste or other suitable
cementing material may be placed in series with the coil,

page_text: A level or plummet or other suitable arrangement and levelling screws or other
means of adjustment are provided to ensure the instrument being always set up in
the same position with regard to the vertical; or the instrument may be suspended
by gimbals.
It will be obvious that my improved electric measuring instrument can be used
to measure either direct or alternating currents.
In order to enable my invention to be fully understood I will proceed to describe
the same by reference to the accompanying drawing in which figure I, which is
diagrammatic shews the needle and the weight pivotted and placed within the
coil; figures II and III are respectively an elevation partly in section and a plan
of a current indicator constructed according to my invention.
Similar letters in all the figures represent similar parts.
A is the laminated soft iron needle attached to a pointer B which indicates the
position of the needle at any given moment on a scale C; D is the weight.
The positions of the needle, pointer and weight are fixed with respect to each
other and they rotate upon a common axis pivotted at E; F is the coil.
In the position G shewn in the diagram in full lines, the force acting on the
needle and tending to move the pointer along its scale is almost entirely the turning
force which in or near to this position is at a maximum.
In and about this position, however, the solenoidal force does not materially help
to turn the needle but expends a part of its force in a direction passing through the
centre E.
The direction of movement of the pointer along the scale is from right to left in
the diagram. If we suppose that a gradually increasing current is passing through
the helices of the coil F, the needle A will at first be turned chiefly by the turning
force of the coils as hereinbefore described and will continue to be turned by the
combined action of the turning force and the solenoidal force each having a turning
moment about the axis E tending to move the pointer B along the scale C from
right to left.
The turning moment supplied by the turning force diminishes becoming zero
when the axis of the needle is at right angles to the plane of the helices, as shewn
in dotted lines at H, while the turning moment about the axis E due to the solenoidal
force increases and may be used to move the pointer and to prolong the scale after
the moment due to the turning force has entirely ceased and has even begun to act
in opposition to its moment.
In this manner I obtain. more equal scale divisions corresponding to equal
increments of current (or electromotive force as the case may be) and a greater
available range.
L Figures I and II is
the terminals.
spirit level; M, M, M, are the levelling screws, T, T, are
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
t
1. An electric measuring instrument in which the needle is operated by the com-
bination of the two forces. hereinbefore called the turning force and the solenoidal
force in the manner substantially as and for the purposes, described:
2. The improved electric measuring instrument hereinbefore described and
represented in the accompanying drawing.
Dated the 22nd day of January 1886.