An Improved Instrument for Measuring Electrical Currents.
Year: 1890

page_text: Date of Application, 27th Mar., 1890
Complete Specification Left, 26th Nov., 1890-Accepted, 26th Mar., 1891
PROVISIONAL SPECIFICATION.
An Improved Instrument for Measuring Electrical Currents.
I, WILLIAM HENRY DOUGLAS, of Stourbridge, in the County of Worcester
Watchmaker, do hereby declare the nature of this invention to be as follows :--
This invention has reference to my former Patent No. 14729 dated
October 29th 1887 for an improved meter for measuring electrical currents and
consists in a simple method of compensation for temperature and also a method of
obtaining tension for accurate measurement.
To obtain these two objects I attach terminals to a plate of metal the terminals
being conveniently separated from each other and connected by a strip of metal
forming a bridge. The conductivity of the bridge being sufficiently small to resist
the current is heated in proportion to the strength of the current passing through.
The bridge is held in tension midway by a spring or weight. The expansion in the
bridge caused by the resistance to the current is thus induced to rise or dip as
desired. The rise or dip is then measured by multiplying gear. The compensation
for temperature is effected by attaching the terminals to the before mentioned plate
which must be of the same co-efficiency of expansion as the metal used to form the
bridge.
Dated this 26th day of March 1890.
HENRY F. TALBOT,
7, Cherry Street, Birmingham, Agent for the Applicant.
COMPLETE SPECIFICATION.
An Improved Instrument for Measuring Electrical Currents.
I, WILLIAM HENRY DOUGLAS, of Stourbridge, in the County of Worcester,
Watchmaker, 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, reference being had to the accompanying drawings & to the
letters & figures marked thereon:-
My improvement has reference to my Patent No. 14729 dated Oct. 29th 1887
for an improved meter for measuring electrical currents & consists of a simple
method of compensation for temperature & also a method of obtaining tension for
accurate measurement.
To obtain these objects I attach terminals to a plate or tube of metal the said
terminals being conveniently insulated from each other & connected by a strip of
metal forming a bridge. The cross section of the latter being small it offers a certain
resistance & becomes heated by the current traversing it.
The bridge is held in tension midway by a spring or weight & when any
expansion takes place in the bridge in consequence of the passage of a current it
assumes the form of a curve the extent of which can be measured by suitable levers
acting on the indicator.
The compensation for temperature is effected by the above mentioned plate or
tube having the same coefficient of expansion as the metal used to form a bridge.

page_text: I will now illustrate the method by which I cause the movement of the strip or
bridge to be measured & recorded.
Referring to the drawings Fig. 1 represents a front view of the swinging scythe
shaped scale & its connection with the recording apparatus & elongating strip or
bridge. Fig. 2 is a top view of the parts without the clock, scythe, or counting
apparatus.
The similar letters of reference in both figures refer to the same parts.
(a) is a scythe shaped scale it is fixed on an axle (b) which is pivotted between
the bracket (c) & brass bar (d).
The axle (b) also carries a fixed curved steel piece (e) attached to a collar. (f) is
another axle pivotted between the bracket (g) & brass bar (d). This axle carries
a fixed lever (h) at the end of which is a small roller (i) resting on the curved
piece (e). (k) is the bridge or strip of brass fixed between the two terminals
blocks () & (2) these blocks are insulated from the brass bar (d). Through the
centre of the brass strip (k) is a hole through which a screw passes freely and
having at its upper end the nut (m) which is resting on the strip. The lower part
of the screw terminates in an ivory or other insulating piece (y) through which a
pin passes carrying the metal bow (2) which is hinged to the lever (h). The latter
is constantly pulled downwards by the weight (n) & when the brass strip is elongated
by the heat of the current the roller () presses on the curved arm (e).
When no current passes the lever adjusted by the nut, (m) allows the curved
arm (e) to remain at rest.
(o) is a smooth edged wheel marked with ten divisions fixed on the first axle of
a train of counting wheels. In front of it & on the same axle are three arms (1)
(q) & () fixed rigidly together but the whole can move freely on the axle
which carries the wheel (o).
(s) and (t) are two springs resting on the rim of wheel (o) allowing it to slide in
a forward direction only. The arm (9) being heavier than the arm (p) falls down-
wards but is stopped by the wedge shaped projection (w) fixed on arm (9) resting
on the calibrated curve of the scythe shaped scale.
(e) is a revolving arm with a pin (w) fixed near the end, this arm makes one
revolution every three minutes being driven by a self winding or other clock (y).
As the arm revolves the projecting pin (w) presses on the lever (p) thereby
raising the bridge shaped projection (w) from the scythe shaped scale & at the same
time by means of the spring (*) resting on the rim of the wheel (o) moves the said
wheel forward the required number of degrees representing the amount of current
passing.
When no current is passing & the scythe is hanging at the zero point the revolving
pin (w) does not press the spring sufficiently to cause any movement in the wheel or
recording train. When a current passes & the scythe moved by the curved arm (e)
is deflected the arm (9) drops & the corresponding arm (p) is raised & the greater
the deflection the longer time are the dials in connection with the revolving arm of
the clock so that for a small current (w) only presses on (p) during a portion of the
revolution of the arm (v) & during a stronger current it presses longer causing a
spring () which is fixed on arm () to shift the first counting wheel forward pro-
portionally.
The dials show the consumption of electricity in ampere hours.
Having now particularly described & ascertained the nature of my said inven-
tion in what manner the same is to be performed, I declare that what I claim is :-
(1) The use in the electric circuit of a strip of metal or bridge of such a nature
as to be easily elongated by the passage of a current such strip being held firmly
between terminals fixed on a plate of metal having the same coefficient of expansion
& thus compensating for external changes of temperature.
(2) The combination of lever (h) roller (i) compensating cam (e) by means of
which the movements in the strip are communicated to the calibrated scale.

page_text: (3) The general combination of clockwork index movements & current meter by
means of levers as herein set for for the purpose of measuring electrical currents.
Dated this 25th day of November 1890.
HENRY F. TALBOT,
7, Cherry Street, Birmingham, Agent for the Applicant.