An Improved Instrument for Measuring the Extension of Test Bars, Termed an Extensometer.
Year: 1887

page_text: Date of Application, 12th Jan., 1837
Complete Left, 11th Oct., 1887
Complete Accepted, 11th Nov., 1887
PROVISIONAL SPECIFICATION.
An Improved Instrument for Measuring the Extension of Test Bars,
Termed an Extensometer.
1, WILLIAM CAWTHORNE UNWIN of 7 Palace Gate Mansions, Kensington, London
Civil Engineer do hereby declare the nature of this invention to be as follows:-
Two clips are placed on the Test Bar gripping it between the points of two set
screws in a plane passing through its axis. Each clip carries a very delicate spirit
level. By means of an adjusting screw the lower clip is first levelled. Then by means
of a fine micrometer screw fixed to the lower and pressing on the upper clip, the upper
clip is levelled. A reading taken on the graduated head of the micrometer screw is
then recorded. Differences of readings during the test give the extensions of the
Test bar. The micrometer screw is in a plane nearly bisecting at right angles the
lines connecting the points of the set screws.
Dated this Seventh day of January 1887
WILLIAM CAWTHORNE UNWIN.

page_text: I, WILLIAM CAWTHORNE UNWIN of 7 Palace Gate Mansions, Kensington W.
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 an improved construction of instrument for measuring the
extension of test bars so arranged that the measurements taken are the mean of the
extensions of the two sides of the bar. For this purpose two clips are placed on
the test bar, gripping it between the points of two set screws in a plane passing through
its axis. Each clip carries a very delicate spirit level. By means of an adjusting
screw the lower clip is first levelled. Then by means of a fine micrometer screw fixed
to the lower and pressing on the upper clip, the upper clip is levelled. A reading
taken on the graduated head of the micrometer screw is then recorded. Differences
of recordings during the test give the extensions of the test bar. The micrometer
screw is in a plane nearly bisecting at right angles the lines connecting the points of
the set screws.
DESCRIPTION OF THE DRAWING.
e is an
Fig. 1 shows a front view, Fig. 2 a sectional side view, Fig. 3 a plan and Fig. 4 a
cross section at xx Fig. 2 of the above described apparatus. a and b are the two clips
carrying levels gg and fixed on the test bar by pointed set screws cd.
adjusting screw by which the lower clip is set level. Then the upper clip is levelled
by the accurate micrometer screw on the graduated head of which readings are
taken. It will be seen from the above described construction that as the clips a and b
are connected to each side of the test bar by the screws cd while the measuring
appliance is situated midway between the attachments of the clips, the measured
extension will be the mean extension of the two sides.
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 :
1-An instrument for measuring the extension of a test bar wherein two clips,
attached to a test bar a certain distance apart, have each an attachment on opposite
sides of the bar while the measuring device is situated midway between the points of
attachment, so that the measured extension is the mean of the extensions of the two
sides.
2-In an instrument for measuring the extension of a test bar such as is referred
to in the preceding claim, the combination of the clips a and b having levels 99 and
attached by screw points cd to each side of the test bar, with the setting screw e and
micrometer screw f, arranged and operating substantially as herein described.
Dated this 11th day of October 1887.
ABEL & IMRAY,
Agents for the Applicant.