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IS0
I NT ERN AT1 ON AL ORGAN IZATi O N FOR STA N DA RD IZATl O N
IS0 RECOMMENDATION
R 376
CALIBRATION OF ELASTIC PROVING DEVICES
1 st EDITION
Au g ust 1 964
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The copyright of IS0 Recommendations and IS0 Standards
belongs to IS0 Member Bodies. Reproduction of these
documents, in any country, may be authorized therefore only
by the national standards organization of that country, being
a member of ISO.
For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
Also issued in French and Russian. Copies to be obtained through the national standards organizations.
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BRIEF HISTORY
The IS0 Recommendation R 376, Calibration of Elastic Proving Devices, was drawn up
by Technical Committee ISO/TC 17, Steel, the Secretariat of which is held by the British Stan-
dards Institution (BSI).
Work on this question by the Technical Committee began in 1957 and led, in 1962, to the
adoption of a Draft IS0 Recommendation.
In November 1962, this Draft IS0 Recommendation (No. 521) was circulated to all the
IS0 Member Bodies for enquiry. It was approved, subject to a few modifications of an edi-
torial nature, by the following Member Bodies :
Australia France Spain
Sweden
Austria Germany
Belgium Hungary Switzerland
Brazil India Turkey
Burma Ireland United Kingdom
Canada Italy U.S.A.
U.S.S.R.
Chile Japan
Czechoslovakia Netherlands Yugoslavia
Denmark Portugal
Finland Romania
No Member Body opposed the approval of the Draft.
The Draft IS0 Recommendation was then submitted by correspondence to the IS0 Council,
which decided, in August 1964, to accept it as an IS0 RECOMMENDATION.
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ISO/R 376 - 1964 (E)
Au g ust 1964
IS0 Recommendation R 376
CALIBRATION OF ELASTIC PROVING DEVICES
1. SCOPE
This IS0 Recommendation applies to elastic proving devices for the static verification of testing
machines. It is intended to cover only those devices in which the load is determined by measure-
ment of the elastic deflection of a loaded member. The measurement of the deflection may be
made by mechanical, electrical, optical or other means of sufficient precision and stability.
2. DESIGN REQUIREMENTS FOR ELASTIC PROVING DEVICES
It is recommended that proving devices should be provided with means permitting axial applica-
tion of load, whether tension or compression. (In other cases, it is essential that the self-aligning
device of the machine should be used in conjunction with the proving device).
When the deflection of the device is measured on a scale, the width of the graduation marks on the
scale should be uniform, and the width of the index mark or of the pointer should be approximately
equal to the width of a graduation mark.
No upper limit is set to the number of scale divisions which may be provided on the deflection,
measuring apparatus for the reading corresponding to the full load on the device, but a lower
limit is set to the number of divisions corresponding to the minimum load at which the device
may be used (see clause 4.2). In general, the lower limit for the number of divisions of deflection
will control the minimum load at which the device will be calibrated.
Further, for the purpose of assessing the minimum load at which a device may be used, it will be
assumed, for the purposes of this IS0 Recommendation, that a scale division may not be subdi-
vided by estimation into more than a specified number of sub-divisions, depending on the type of
deflection-measuring apparatus used and the scale spacing. *
In the case of devices incorporating a dial gauge or a micrometer screw, it will be assumed for
this purpose that a division may be subdivided with assurance as follows:
to one half of a scale interval, when the scale spacing is less than 1 mm (0.04 in);
to one fifth of a scale interval, when the scale spacing is 1 mm (0.04 in) or more.
The reading limit so defined should be regarded as the smallest interval of scale reading of the
device for the purpose of defining the minimum load.
For devices incorporating other forms of deflection measuring apparatus, i.e. microscopes, elec-
trical circuits, etc., the calibrating authority should determine the smallest interval of scale reading
which should be used for this purpose, having regard to both the setting and reading of the deflec-
tion-measuring apparatus.
The readings of deflection of the proving device should not be subject to variation by outside
causes, e.g. by normal variations in power supply required, such as changes in line voltage or
frequency.
The device should be suitably identified by the maker’s name, serial number and maximum load.
* This does not, of course, impose any restriction on the calibrating authority or the user when reading the device.
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ISO/R 376 - 1964 (E)
3. CALIBRATION
3.1 Determination of deflection. A deflection is defined as the difference between a reading
under load and the mean of the no-load readings before and after loading. If more than one
reading is interposed between the actual no-load readings, and a change of the latter has
taken place, a uniformly progressive change in no-load readings should be assumed in order
to determine the no-load reading applicable to each load reading. If a uniformly progressive
change cannot be assumed, but the change is small (see Table below, column 7), the deflection
should not be corrected. However, the second no-load reading will be taken as the basis
of the following readings.
The maximum change of no-load reading must not exceed the percentage of the deflection
under full load as specified in the Table, column 7. The calibrating authority can use its
discretion as to whether to return to zero load after each deflection.
Table. - Grading of elastic proving devices
314
Requirements for elastic proving devices
Grade Maximum load Requirements for calibrating
(These requirements include permissible inaccuracies
of device loads
of the calibrating loads)
For linearity
For repeatability
(optional)
Lack of re- Maximum Change of Change of Departure of
At each cali-
peatability of permissible bration load, no-load read- no-load read- linearity
calibrating ing during indicated by
error of load difference ing in over-
load applied applied to load test, calibration, calibration
between max-
to device, device, ex- imum and expressed as expressed as curve, ex-
expressed as pressed as percentage of percentage of pressed as
minimum of
percentage of percentage of deflection deflection percentage of
:he deflection:
applied load. applied load. expressed, as under full under full calibration
load. load. factor of
percentage of
CUNO.
average
deflection.
Maximum permissible
1 Up to and in-
cluding 50 000
kgf (50 tons-
force) 0.01 0.2
f 0.02 o. 1 o. 1 rt 0.1
Over 50 O00
kgf (50 tons-
force), up to
and including
500000 kgf
(500 tons-
force) 0.10 & 0.2 0.4 0.1 0.1 rt 0.3
2 Up toandin-
cluding 50 000
kgf (50 tons-
force) 0.01 f 0.02 0.4 0.2 0.2 f 0.2
Over 50 O00
kgf (50 tons-
force), up to
and including
500000 kgf
(500 tons-
0.2
force) 0.10 rt 0.2 0.6 0.2 f 0.4
Noms
1. An elastic proving device of maximum load above 50 O00 kgf (50 tons-force) is not inherently
less accurate than a device of 50 O00 kgf (50 tons-force) or less, maximum load. For loads
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ISO/R 376 - 1964 (E)
up to 50000 kgf (50 tons-force), dead weights are generally available for the calibration
of elastic proving devices, but for loads above 50 O00 kgf (50 tons-force) secondary standards
which are less accurate are usually employed. The requirements for the proving devices are
therefore made less stringent so as to allow for the less accurate calibration loads.
2. When an elastic proving device of maximum load above 50 O00 kgf (50 tons-force) is being
calibrated, and the requirements of clause 4.2 allow grade 1 repeatability to be given for a
load of 40 O00 kgf (40 tons-force) or less, then all calibration loads of 50 O00 kgf (50 tons-
force) and less should be of the greater accuracy, i.e. having repeatability within 0.01 per cent
and maximum permissible errors of & 0.02 per cent.
3.2 Overload test. Before any calibration or re-calibration, the device should be overloaded
four times in the manner (tension or compression or both) in which it is intended to be used,
to a load of not less than 8 per cent and not more than 10 per cent in excess of the full load.
The overload should be maintained for a period of 1 to 1 ?I$ minute. The difference between
the no-load readings before and after the first overload should be ignored, but the change
in no-load reading produced by any one subsequent overload should not exceed the per-
centage of the deflection under full load, as specified in the Table, column 6.
3.3 Accuracy of applied loads. The repeatability and the accuracy of the loads applied for
calibration should be within the limits specified in the Table, columns 3 and 4.
It is recommended that elastic proving devices should be calibrated in terms of technical
units * of force based on the kilogramme-mass or the pound-mass (or the multiple units,
the metric tonne-mass equal to 1000 kilogrammes-mass and the (long) ton-mass equal to
2240 pounds-mass). The kilogramme-force (kgf) is that force which, acting on one kilo-
gramme-mass, will give it an acceleration of 980.665 cm/s2 (32.174 ft/s2); the pound-force
(Ibf) is that force which, acting on one pound-mass will give to it an acceleration of
980.665 cm/s2. If local gravitational units of force are used during the calibration, it is
recommended that the results are converted to be in terms of technical units of force.
NOTE. - The newton (N) is that force which, acting on one kilogramme-mass, will give it an acceleration
of 1 m/s2.
3.4 Conditions of loading. The time interval between any two successive loadings should be as
uniform as possible, and no reading should be taken less than 30 seconds after a change of
load. Calibration of an elastic proving device should generally be carried out at a tempera-
ture of 20 f 1 "C for temperature climates, and at 27 f 1 "C for tropical climates. The
parts of the device used to carry out the tests should be kept at the test tem
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