ASTM E83-23

Standard Practice for Verification and Classification of Extensometer Systems

ABSTRACT
This practice covers procedures for the verification and classification of extensometer systems, but it is not intended to be a complete purchase specification. The practice is applicable only to instruments that indicate or record values that are proportional to changes in length corresponding to either tensile or compressive strain. Extensometer systems are classified on the basis of the magnitude of their errors. The apparatus for verifying extensometer systems shall provide a means for applying controlled displacements to a simulated specimen and for measuring these displacements accurately. Extensometer systems shall be classified in accordance with the requirements as to maximum error of strain indicated: Class A; Class B-1; Class B-2; Class C; Class D; and Class E. Extensometer systems shall be categorized in three types according to gage length: Type 1; Type 2; and Type 3. A verification procedure for extensometer systems shall be done in accordance with the specified requirements.
SCOPE
1.1 This practice covers procedures for the verification and classification of extensometer systems, but it is not intended to be a complete purchase specification. The practice is applicable only to instruments that indicate or record values that are proportional to changes in length corresponding to either tensile or compressive strain. Extensometer systems are classified on the basis of the magnitude of their errors.  
1.2 Because strain is a dimensionless quantity, this document can be used for extensometers based on either SI or US customary units of displacement.  
Note 1: Bonded resistance strain gauges directly bonded to a specimen cannot be calibrated or verified with the apparatus described in this practice for the verification of extensometers having definite gauge points. (See procedures as described in Test Methods E251.)  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Dec-2022
• ICS: 19.060 - Mechanical testing
• Technical Committee: E28 - Mechanical Testing
• Drafting Committee: E28.01 - Calibration of Mechanical Testing Machines and Apparatus

Relations

• Refers: ASTM E251-20a - Standard Test Methods for Performance Characteristics of Metallic Bonded Resistance Strain Gages
• Effective Date: 01-Jun-2020
• Refers: ASTM E251-20 - Standard Test Methods for Performance Characteristics of Metallic Bonded Resistance Strain Gages
• Effective Date: 01-May-2020
• Refers: ASTM E251-92(2014) - Standard Test Methods for Performance Characteristics of Metallic Bonded Resistance Strain Gages
• Effective Date: 15-Apr-2014
• Refers: ASTM E6-09b - Standard Terminology Relating to Methods of Mechanical Testing
• Effective Date: 15-May-2009
• Refers: ASTM E6-09be1 - Standard Terminology Relating to Methods of Mechanical Testing
• Effective Date: 15-May-2009
• Refers: ASTM E21-09 - Standard Test Methods for Elevated Temperature Tension Tests of Metallic Materials
• Effective Date: 01-Apr-2009
• Refers: ASTM E6-09a - Standard Terminology Relating to Methods of Mechanical Testing
• Effective Date: 01-Apr-2009
• Refers: ASTM E251-92(2009) - Standard Test Methods for Performance Characteristics of Metallic Bonded Resistance Strain Gages
• Effective Date: 01-Apr-2009
• Refers: ASTM E6-09 - Standard Terminology Relating to Methods of Mechanical Testing
• Effective Date: 01-Jan-2009
• Refers: ASTM E6-08a - Standard Terminology Relating to Methods of Mechanical Testing
• Effective Date: 01-Oct-2008
• Refers: ASTM E6-08 - Standard Terminology Relating to Methods of Mechanical Testing
• Effective Date: 01-Feb-2008
• Refers: ASTM E6-07b - Standard Terminology Relating to Methods of Mechanical Testing
• Effective Date: 01-Nov-2007
• Refers: ASTM E6-07a - Standard Terminology Relating to Methods of Mechanical Testing
• Effective Date: 01-Jun-2007
• Refers: ASTM E6-07 - Standard Terminology Relating to Methods of Mechanical Testing
• Effective Date: 01-Mar-2007
• Refers: ASTM E6-06 - Standard Terminology Relating to Methods of Mechanical Testing
• Effective Date: 01-Apr-2006

Overview

ASTM E83-23: Standard Practice for Verification and Classification of Extensometer Systems provides a comprehensive framework for verifying and classifying extensometer systems used in measuring material strain during tensile or compressive testing. This standard ensures that extensometer systems provide accurate and reliable strain measurements, which are crucial for mechanical testing of materials in various industries. ASTM E83-23 is applicable to extensometer systems that indicate or record strain as a function of dimensional changes and is relevant for manufacturers, laboratories, and quality assurance professionals who require traceable and standardized measurement procedures.

Key Topics

• Scope of Application: Applies to extensometers that record values proportional to changes in specimen length, in both tensile and compressive directions. Excludes bonded resistance strain gauges directly attached to specimens.
• Classification by Error Magnitude: Extensometer systems are classified into Class A, B-1, B-2, C, D, and E based on the maximum allowable strain error and gauge length precision.
  • Class A provides highest precision; Classes B-1 and B-2 suit general laboratory applications; Classes C, D, and E are for broader tolerances.
• Verification Procedures: Involves applying known displacements to a simulated specimen via calibrated apparatus, ensuring accuracy by comparing indicated versus actual strain values.
• Types of Extensometer Systems:
  • Type 1: Devices that define both gauge length and sense extension (e.g., clip-on extensometers).
  • Type 2: Devices where gauge length is defined by specimen geometry.
  • Type 3: Devices intrinsically sensing strain (e.g., digital or video extensometers).
• Verification Frequency and Reporting: Recommends annual verification of extensometer systems, not to exceed 18 months between verifications. Detailed reporting requirements ensure traceability and accountability.
• Spot Checks and Accuracy Assurance: Offers guidance for routine spot checks to confirm ongoing system accuracy between formal verifications.
• Optical Extensometer Systems: Includes specific annex requirements for laser, video, and virtual optical extensometers regarding setup, field of view, working distance, and verification of various system components.

Applications

ASTM E83-23 is widely utilized in:

• Materials Testing Laboratories: Ensures that strain measurements during tensile, compression, or cyclic testing are accurate and traceable.
• Quality Assurance: Used by manufacturers and third-party testing agencies to validate the performance of extensometer systems for compliance and certification.
• Calibration Services: Provides the framework for service providers to calibrate and certify extensometers according to internationally recognized standards.
• Research and Development: Integral for developing and validating new materials, as reliable strain data is critical for material behavior analysis.
• Optical Measurement Technologies: Addresses modern extensometer systems such as video extensometers and laser-based systems, ensuring their verification aligns with traditional mechanical systems.

Related Standards

For comprehensive strain measurement and verification, users of ASTM E83-23 should also reference:

• ASTM E6: Terminology Relating to Methods of Mechanical Testing
• ASTM E21: Test Methods for Elevated Temperature Tension Tests of Metallic Materials
• ASTM E251: Test Methods for Performance Characteristics of Metallic Bonded Resistance Strain Gages
• JCGM 100:2008: Guide to the Expression of Uncertainty in Measurement

By adhering to ASTM E83-23, organizations can ensure that extensometer data is accurate, traceable, and compliant with both U.S. and international standards, supporting reliable material testing and validation processes.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E83 − 23
Standard Practice for
Verification and Classification of Extensometer Systems
This standard is issued under the fixed designation E83; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* E251 Test Methods for Performance Characteristics of Me-
tallic Bonded Resistance Strain Gages
1.1 This practice covers procedures for the verification and
2.2 Other Standards:
classification of extensometer systems, but it is not intended to
JCGM 100:2008 Evaluation of measurement data – Guide to
be a complete purchase specification. The practice is applicable
the expression of uncertainty in measurement
only to instruments that indicate or record values that are
proportional to changes in length corresponding to either
3. Terminology
tensile or compressive strain. Extensometer systems are clas-
sified on the basis of the magnitude of their errors.
3.1 Definitions:
3.1.1 In addition to the terms listed, see Terminology E6.
1.2 Because strain is a dimensionless quantity, this docu-
3.1.2 calibration—a determination of the calibration factor
ment can be used for extensometers based on either SI or US
for a system using established procedures.
customary units of displacement.
3.1.3 calibration factor—the factor by which the change in
NOTE 1—Bonded resistance strain gauges directly bonded to a speci-
extensometer reading must be multiplied to obtain the equiva-
men cannot be calibrated or verified with the apparatus described in this
practice for the verification of extensometers having definite gauge points. lent strain.
(See procedures as described in Test Methods E251.)
3.1.3.1 Discussion—For any extensometer, the calibration
1.3 This standard does not purport to address all of the factor is equal to the ratio of change in length to the product of
safety concerns, if any, associated with its use. It is the the gauge length and the change in the extensometer reading.
responsibility of the user of this standard to establish appro- For direct-reading extensometers the calibration factor is unity.
priate safety, health, and environmental practices and deter-
3.1.4 compressometer—a specialized extensometer used for
mine the applicability of regulatory limitations prior to use.
sensing negative or compressive strain.
1.4 This international standard was developed in accor-
3.1.5 deflectometer—a specialized extensometer used for
dance with internationally recognized principles on standard-
sensing of extension or motion, usually without reference to a
ization established in the Decision on Principles for the
specific gauge length.
Development of International Standards, Guides and Recom-
3.1.6 dot/line tracking optical extensometer system (DLT),
mendations issued by the World Trade Organization Technical
n—an optical extensometer system that uses marks at an
Barriers to Trade (TBT) Committee.
initially known distance, physically placed on a specimen or
calibration fixture, to establish the gauge length value for
2. Referenced Documents
determination of strain.
2.1 ASTM Standards:
3.1.7 error, in extensometer systems—the value obtained by
E6 Terminology Relating to Methods of Mechanical Testing
subtracting the correct value of the strain from the indicated
E21 Test Methods for Elevated Temperature Tension Tests of
value given by the extensometer system.
Metallic Materials
3.1.8 extensometer, n—a device for sensing strain.
3.1.9 extensometer systems—a system for sensing and indi-
This practice is under the jurisdiction of ASTM Committee E28 on Mechanical
cating strain.
Testing and is the direct responsibility of Subcommittee E28.01 on Calibration of
3.1.9.1 Discussion—The system will normally include an
Mechanical Testing Machines and Apparatus.
Current edition approved Jan. 1, 2023. Published February 2023. Originally
extensometer, conditioning electronics and auxiliary device
approved in 1950. Last previous edition approved in 2016 as E83 – 16. DOI:
10.1520/E0083-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Available from International Organization for Standardization (ISO), ISO
Standards volume information, refer to the standard’s Document Summary page on Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier,
the ASTM website. Geneva, Switzerland, http://www.iso.org.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E83 − 23
(recorder, digital readout, computer, etc.). However, com- similar to normal operation (that is, possibly without contact
pletely self-contained mechanical devices are permitted. An for some optical extensometers).
extensometer system may be one of three types.
3.2 virtual optical extensometer system, n—an optical ex-
tensometer system in which the initial datum points used to
3.1.10 Type 1 extensometer system, n—an extensometer
establish the gauge length value for determination of strain are
system which both defines gauge length and senses extension,
chosen by the user based on a location in the image in software
for example, a clip-on strain gauge type with conditioning
– the gauge length is not defined by discrete marks on the
electronics.
specimen.
3.1.11 Type 2 extensometer system, n—an extensometer
3.3 working distance, (WD), n—the physical distance that
which senses extension and the gauge length is defined by
the optical extensometer system is from the surface of the
specimen geometry or specimen features such as ridges or
specimen or verification apparatus, the distance is measured
notches.
from the front of the optical extensometer system.
3.1.11.1 Discussion—A Type 2 extensometer is used where
3.3.1 Discussion—The WD measurement can be made from
the extensometer gauge length is determined by features on the
the camera body to the front of the specimen or verification
specimen, for example, ridges, notches, or overall height (in
apparatus. While it is not important where the physical distance
case of compression test piece). The precision associated with
is measured from it is important to measure the distance and
gauge length setting for a Type 2 extensometer should be
report where the measurements were made. Doing this will
specified in relevant test method or product standard. The
enable the user to recreate the conditions under which the
position readout on a testing machine is not recommended for
optical extensometer system was verified.
use in a Type 2 extensometer system.
3.1.12 Type 3 extensometer system, n—an extensometer
4. Verification Apparatus
system which intrinsically senses strain (ratiometric principle),
4.1 The apparatus for verifying extensometer systems shall
for example, video camera system.
provide a means for applying controlled displacements to a
3.1.13 gauge length (L), n—the original length of that
simulated specimen and for measuring these displacements
portion of the specimen over which strain or change of length
accurately. It may consist of a rigid frame, suitable coaxial
is determined.
spindles, or other fixtures to accommodate the extensometer
3.1.13.1 Discussion—If the device is used for sensing ex-
being verified, a mechanism for moving one spindle or fixture
tension or motion, and gauge length is predetermined by the
axially with respect to the other, and a means for measuring
specimen geometry or specific test method, then only resolu-
accurately the change in length so produced, or any other
tion and strain error for a specified gauge length should
device or mechanism that will accomplish the purpose equally
determine the class of extensometer system.
well. The mechanism provided for moving one spindle relative
to the other shall permit sensitive adjustments. The changes in
3.1.14 laser optical extensometer system, n—an optical
length shall be measured, for example, by means of an
extensometer system that uses a laser to track and measure the
interferometer, calibrated standard gauge blocks and an
extension/strain.
indicator, a calibrated micrometer screw, or a calibrated laser
3.1.15 resolution of the strain indicator—the smallest
measurement system. If standard gauge blocks and an
change in strain that can be estimated or ascertained on the
indicator, or a micrometer screw, are used, they shall be
strain indicating apparatus of the testing system, at any applied
calibrated and their limits of accuracy and sensitivity stated.
strain.
The errors of the verification apparatus shall not exceed one
3.1.16 resolution of the digital type strain indicators (nu-
third of the permissible error of the extensometer.
meric displays, printouts, and so forth)—the resolution is the
4.2 The verification apparatus shall be calibrated at intervals
smallest change in strain that can be displayed on the strain
not to exceed two years.
indicator (may be a single digit or a combination of digits) at
any applied strain. NOTE 2—He-Ne laser interferometer measurement systems based on
the 0.633 μm wavelength line are considered to be primary-based
3.1.16.1 Discussion—If the strain indication, for either type
displacement standards and do not require recalibration.
of strain indicator, fluctuates more than twice the resolution, as
4.3 If the verification apparatus is to be used to verify
described in 3.1.15 or 3.1.16, the resolution expressed as a
extensometers used for bidirectional tests, the errors of the
strain shall be equal to one-half the range of fluctuation.
verification apparatus should be measured in both directions of
3.1.17 verification—a determination that a system meets the
travel so as to include any backlash present.
requirements of a given classification after calibration accord-
ing to established procedures.
3.1.18 verification apparatus—a device for verifying exten-
A review of some past, current, and possible future methods for calibrating
someter systems.
strain measuring devices is given in the paper by Watson, R. B., “Calibration
Techniques for Extensometry: Possible Standards of Strain Measurement,” Journal
3.1.18.1 Discussion—This device is used to simulate the
of Testing and Evaluation, JTEVA, Vol. 21, No. 6, November 1993, pp. 515–521.
change in length experienced by a test specimen as a result of
A letter from NIST (National Institute of Standards and Technology) has been
the applied force. The extensometer may either be attached
filed at ASTM International Headquarters and may be obtained by requesting
directly to the mechanism or interfaced with it in a manner Research Report RR: E28-1013.
E83 − 23
5. Verification Procedure for Extensometer Systems inherent measurement accuracy that is the important factor
rather than the error between the chosen length and the actual.
5.1 General Requirements—The verification of an exten-
someter system should not be done unless the components of NOTE 4—An example of an extensometer that is described by 5.2.3 is
an optical extensometer that measures the position of “flags” attached to
the system are in good working condition. Thoroughly inspect
the test specimen. The flags are positioned at the approximate required
all parts associated with smooth operation of the instrument to
gauge length and the instrument measures the position of the flags (the
ensure there are no excessively worn components. Repair or
actual gauge length) before and after the specimen is stressed. Although
replace parts as necessary. Remove any dirt particles which
this kind of device usually has a stated accuracy of gauge length, it must
may have accumulated through normal use of the instrument. be verified by either direct or indirect methods at the appropriate gauge
lengths.
Verification of the system shall be performed whenever parts
are interchanged or replaced. Some extensometers have parts
5.3 Position of Extensometer—Carefully position the exten-
that are designed to be interchanged such as gauge length
someter on or interface it to the verification device in the same
extenders and lenses used with video extensometers. If these
manner as it is normally used for typical specimens. For
parts can be shown to be interchangeable without degrading the
extensometers that attach directly to the specimen, the verifi-
verified classification of the extensometer, they may be inter-
cation device should allow attachment to pieces that are similar
changed between scheduled verifications of the extensometer.
to the specimen on which the extensometer will be attached.
Verification of the extensometer with all combinations of
5.4 Temperature Control—Verify the extensometer at ap-
interchangeable parts that are anticipated to be used for testing
proximately the same temperature at which it will be used.
is required.
Allow sufficient time for the verification device and extensom-
5.1.1 The verification of an extensometer system refers to a
eter to reach satisfactory temperature stability. Maintain tem-
specific extensometer used with a specific readout device.
perature stability by excluding drafts throughout the subse-
Unless it can be demonstrated that autographic extensometers
quent verification. Record the temperature during each
and recorders of a given type may be used interchangeably
verification run.
without introducing errors that would affect the classification
of the extensometer, the extensometer shall be calibrated with NOTE 5—Extensometers used for high-temperature testing may be
verified at ambient temperature to insure proper operation, but fixtures
the readout device with which it is to be used.
should be designed to verify performance at the actual test temperature.
5.1.2 Prior to the initial verification, the extensometer
This is especially true with optical extensometers which may be adversely
should be calibrated according to the manufacturer’s instruc-
affected by air density changes associated with thermal gradients and
tions or established procedures. The calibration procedure may turbulence, environmental chamber windows, or specimen changes due to
the environment. See Appendix X2.
include adjustment of span or determination of calibration
factor, or both.
5.5 Method of Reading—Read the instrument or, in the case
of an autographic extensometer, measure the record in the same
5.2 Gauge Length Measurement Method—Measure the
manner as during use.
gauge length of self-setting instruments by either the direct or
5.5.1 For extensometer with dial micrometers or digital
indirect method.
readouts, the readings shall be recorded. Extensometers that
NOTE 3—The following is an example of an indirect method. Set the
use autographic methods shall have their charts read and
extensometer to its starting position and mount it on a soft rod of the
recorded using a suitable measuring device, such as a vernier
typical specimen size or diameter. After the extensometer is removed,
or dial caliper. The use of an optical magnifying device is
measure the distance between the marks left by the gauge points (or knife
edges). If there are four or more gauge points, take the average of the recommended when reading and measuring autographic re-
individual lengths as the gauge length. The differences between individual
cords.
measurements shall not exceed the tolerance given for the class of
extensometer. If there are two gauge points (or knife edges), but on NOTE 6—When autographic extensometer systems are used, care
opposite sides of the specimen, attach the extensometer twice rotating it should be taken to minimize errors introduced by variances in the graph
180° with respect to the rod. Take the average of the lengths thus paper. These errors can be due to dimensional changes from reproduction
established on each side of the rod as the gauge length. or humidity changes. Direct measurement of the trace soon after it was
made eliminates the graph paper errors and is desirable for systems
5.2.1 Make two measurements of the gauge length. Deter-
verification.
mine and record the error from each measurement, which is the
NOTE 7—If an extensometer is equipped with a dial micrometer, it may
difference between the measured gauge length and the speci- be necessary to lightly tap the dial micrometer to minimize the effects of
friction and to ensure that the most stable and reproducible readings are
fied gauge length, expressed as a percent of the specified gauge
obtained. If the dial micrometer is tapped during the verification
length.
procedure, include this information in the report.
5.2.2 For extensometer devices that do not have a self-
5.6 Zero Adjustment—After temperature stability has been
setting gauge length during use, such as deflectometers and
achieved, displace the verification device (with extensometer
some high-temperature tensile or creep extensometers, verifi-
in the test position) to a slightly negative value and return to
cation run errors should be calculated using the gauge length
zero. If the reading does not return to zero, adjust and repeat
for which the device is used. Separate classifications should be
the procedure until the reading does return to zero.
established for each gauge length or range used.
5.2.3 Some extensometers have the capability to measure 5.7 Number of Readings—For any strain range, verify the
the gauge length set by or chosen by the user. If this extensometer system by applying at least five displacement
measurement is used in the calculation of strain, then it is the values, not including zero, at least two times, with the
E83 − 23
class, the lower limit (verification range) would be 0.00005 in. × 100 =
difference between any two successive displacement applica-
0.005 in., or 0.5 % strain. The suitable verification points for a single range
tions being no greater than one-third the difference between the
extensometer system would be in percent strain 0.5, 1.0, 2.0, 3.5, 5, 10, 20,
selected maximum and minimum displacements.
35, and 50. (See for single range system Fig. X1.1 and Fig. X1.2 for
5.7.1 Extensometers need not be verified beyond the range
multirange.)
over which they will be used. Multi-range (multi-
5.8 Number of Runs—Take at least two complete sets of
magnification) extensometers shall be verified for each range to
extensometer readings for the same changes of length. After
be used.
the first run, an operation that simulates normal operation
NOTE 8—If the connection between the gauge points attached to the
should be used to check repeatability. An extensometer that
specimen and the indicating device is made through geared wheels or
attaches directly to the specimen should be removed and then
micrometer screws, relatively large periodic errors may exist which might
reattached to the verification device between runs. An exten-
not be disclosed by this overall procedure. For such extensometers it may
someter that does not attach directly to the specimen should be
be necessary to take additional readings within one turn of any geared
wheel, micrometer screw, or the travel of one tooth of any meshing gear. moved away from the verification device (or the device moved
away from the extensometer) to simulate the changing of test
5.7.2 When it is desired to establish the range of an
specimens.
extensometer system designed to automatically select or extend
5.8.1 If the initial verification run (the “as found” run)
ranges below 10 % of full scale without the influence of the
produces satisfactory results which classify an extensometer
operator, the number of readings shall depend on how many
system according to Table 1 specifications, then the data may
overlapping decades are in the range. Extensometer readings
be used as run—one of the two required for the verification
should be chosen starting with the minimum reading and are
report.
grouped in overlapping decades such that the maximum
5.8.2 If the initial verification run produces results which are
reading on one decade is the minimum on the next decade.
outside of expectations, for example, Class C instead of B1,
There are to be at least five strain applications per decade,
and adjustments are necessary, then this first verification run
unless the maximum, or the minimum strain on the range is
might be reported “as found” data and used in accordance with
reached before completing the decade. Strain (displacements)
applicable quality control programs. Calibration adjustments
in each decade are to be approximately 1:1, 2:1, 4:1, 7:1, and
may then be made to the extensometer system after which two
10:1, starting with the minimum strain in each decade.
required verification runs shall be conducted and reported on
5.7.2.1 In no case should the distance between two succes-
the verification report and certificate.
sive strains (displacements) within a decade differ by more
5.8.3 The algebraic difference between errors of the two
than one-third the difference between the minimum and maxi-
verification runs shall not exceed the required Classification
mum strains in that decade. Strains in the second successive
criteria listed in Table 1.
run are to be approximately the same as those of the first run.
Report all percent values of accuracy, and report the indicator
5.9 Direction of Verification Displacement:
resolution at least once per decade.
5.9.1 Extensometers Used for Unidirectional Tests—
5.7.3 Lower Limit Criteria—as indicated in Table 1, all
Extensometers used for unidirectional tests (for example,
verified strain readings must have a resolution at least one-half
tension tests) shall be verified by applying displacement in the
the allowable error, that is, the resolution is a limiting factor to
direction of testing normally used. If start-up backlash is
determine a lower limit of the range. The lowest verified strain
evident, the verification device (with extensometer in place)
reading must be at least 100 times the indicator resolution.
may be displaced to a slightly negative value and returned to
Extensometer results used below the lowest verified strain
zero before each run.
reading may not comply with the error limit specified by this
NOTE 10—This verification procedure does not measure the initial
standard practice.
backlash in the extensometer that may appear after it is first attached to the
NOTE 9—Example: For an extensometer with a gauge length of 1 in. specimen. If the extensometer is used with open or closed loop-type test
and 50 % strain, the full scale displacement value is 0.5 in. If the machine equipment in load control, the users should disregard readings taken
(system) resolution is 0.00005 in., which meets the criteria for the B1 during the initial part of the loading curve. If the extensometer is used with
TABLE 1 Classification of Extensometer Systems
A B
Classification Relative Error of Resolution not to Exceed the Greater of: Error of Strain not to Exceed the Greater of:
gauge Length (max %)
(See 5.2)
Fixed Value % of Reading Fixed Error Relative Error
(in./in., m/m) (in./in., m/m) (% of strain)
Class A ±0.1 0.00001 0.05 ±0.00002 ±0.1
Class B-1 ±0.25 0.00005 0.25 ±0.0001 ±0.5
Class B-2 ±0.5 0.0001 0.25 ±0.0002 ±0.5
Class C ±1 0.0005 0.5 ±0.001 ±1
Class D ±1 0.005 0.5 ±0.01 ±1
Class E ±1 0.05 0.5 ±0.1 ±1
A
Class A classification is very difficult to achieve at short (1 in. (25 mm) or less) gauge lengths, so the commercial availability of an extensometer system that meets this
requirement may be very limited or nonexistent.
B
The strain of an Extensometer System is the ratio of applied extension to the gauge length.
E83 − 23
closed loop test equipment in strain control, the backlash could result in
system (extensometer and readout device) individually and
large tension or compression loads during the initial part of the loading
also in combinations that would be used simultaneously. As an
curve.
alternative, after individual verifications have been made, the
5.9.2 Extensometers Used for Bidirectional Tests—
combination can be checked at three points (about 20 %, 50 %,
Extensometers used for bidirectional tests (for example, hys-
and 90 % of full scale range are recommended); and, if values
teresis tests, fatigue tests, and so forth) (See Appendix X3)
for each system do not differ from the individual verification
shall be verified by applying both increasing and decreasing
values by more than 20 % of the class tolerance, the combined
values of displacement over the total range of intended use.
system shall be considered to meet the same requirements as
Displace the verification device (with extensometer in place) to
the individual systems. If readout devices are always used in
a slightly negative value and return to zero before each run.
combination, individual verifications are not required when the
During each run, displace the extensometer to the maximum
combined system is verified as a unit.
positive value, then to the maximum negative value, and then
back to zero, stopping at each verification point along the way
8. Verification of Data Acquisition Systems
in each direction.
8.1 Extensometer systems in which strain values are indi-
5.10 Determination of Errors—Calculate the error of the
cated on displays or printouts of data acquisition systems, be
extensometer system for each change in length of the verifi-
they instantaneous, delayed, stored or retransmitted, which are
cation apparatus. Errors are based on net values from the zero
verified in accordance with the provisions of Section 5 and
point to each successive verification point, not on increments
classified in accordance with the provisions of Section 6, shall
between verification points.
be deemed to comply with this practice.
6. Classification of Extensometer Systems
9. Time Interval Between Verifications
6.1 Classify extensometer systems in accordance with the
9.1 It is recommended that extensometer systems be verified
requirements as to maximum error of strain indicated by the
annually unless more frequent verification is required to
extensometer system shown in Table 1. The maximum allow-
comply with product or customer specifications. In no case
able error in each class is the fixed error or the variable error,
shall the time interval between verifications exceed 18 months
whichever is greater. The fixed error will establish the maxi-
unless an extensometer is being used on a long-time test
mum allowable error for readings near zero, but the variable
running beyond the 18-month period. In such cases, the
error may establish the maximum allowable error for readings
extensometer system shall be verified immediately after
near full scale. Two examples of this procedure are presented
completion of the test. (See Note 12.)
in Appendix X1. In addition, the gauge length error for Type 1
9.1.1 An extensometer system shall not be used after an
extensometers shall not exceed the greater of the values shown
adjustment or repair that could affect its accuracy without first
in Table 1.
verifying its accuracy utilizing the procedure described in this
6.1.1 Type 2 extensometer systems shall be classified using
practice.
the smallest gauge length for which they are used. They may be
NOTE 12—If a test is expected to last more than 18 months, it is
verified at additional gauge lengths if desired.
recommended that the extensometer system be verified immediately
6.1.2 Type 3 extensometer systems, operating over a range
before as well as upon completion of the test.
of gauge lengths, shall be verified at the minimum and
maximum gauge lengths used. They may be verified at
10. Accuracy Assurance Between Verifications
additional gauge lengths if desired.
10.1 Some product-testing procedures may require daily,
NOTE 11—For Type 3 systems, precision marked, divided test pieces
weekly, or monthly spot checks to ascertain that an
may be used to establish known gauge lengths on the calibration device.
extensometer, recorder, or display, and so forth, or combina-
Known extensions enable the applied strains to be set. These applied
tions thereof etc., are capable of producing accurate strain
strains are compared with the indicated strains from the Type 3 exten-
values between the verifications specified in Section 9. Spot
someter systems, in order to establish its classification in accordance with
the requirements for resolution and strain error in Table 1.
checks may be performed on ranges of interest or at strain
levels of interest utilizing a verification device that complies
6.2 Separate classifications may be established for different
with Section 4 for the strain level(s) at which the spot checks
ranges of multi-range (multiple-magnification) extensometer
are made.
systems.
10.2 Check the extensometer gauge length (see 5.1).
7. Verification of Multiple Strain Readouts
10.3 Make spot checks of extensometer readings at approxi-
7.1 When an extensometer is to be used with two or more
mately 10 % and 50 % of a range unless otherwise agreed upon
readout devices (for example, a graphic recorder and a digital
or stipulated by the material supplier or user.
readout), steps must be taken to assure that errors are not
introduced by interactions (mechanical or electrical) between 10.4 The extensometer gauge length and strain measure-
the readout devices or between the readouts and the ment errors shall not exceed the allowable errors at the spot
extensometer, and that values from each readout device satisfy check points for the specified class of extensometer. Should
appropriate performance criteria. (Different accuracy classifi- errors be greater than allowable at any of the spot check points,
cations could be given to the systems using different readout the extensometer system is to be completely verified immedi-
devices.) This can best be accomplished by verifying each ately.
E83 − 23
10.5 When spot checks are made, a clear, concise record 11.1.8 Error in gauge length for each measurement of gauge
must be maintained as agreed upon between the supplier and length.
the user. The record shall contain gauge length and spot check
11.1.9 Error and relative error of the extensometer for each
test data; the name, serial number, verification date, verification
extensometer reading, the maximum algebraic error difference
agency of the verification device(s) used to make spot checks;
(repeatability) and the associated resolution for each range
the name of person making the spot check; and documentation
(decade).
of the regular verification data and schedule.
11.1.10 Class of the extensometer system. If separate clas-
sifications are established for various ranges, report the range
10.6 The extensometer system shall be considered verified
(or magnification) and strain values associated with each
up to the date of the last successful spot check verification
classification.
provided that the extensometer system is verified in accordance
with Section 5 on a regular schedule in accordance with 11.1.11 If the classification applies to bidirectional testing, it
shall be so stated. Otherwise, the classification shall be
Section 9. Otherwise, spot checks are not valid.
considered to be unidirectional in the direction of normal use
11. Report
(that is, opening for tension testing, closing for compression
11.1 The report shall include the following: testing, and so forth).
11.1.1 Method of gauge length verification used.
11.1.12 The name of the person performing the classifica-
11.1.2 Serial numbers and names of the manufacturers of all
tion and the date it was performed.
apparatus used in verifying the extensometer system.
11.2 Information to be available upon request shall include
11.1.3 Serial number and name of the manufacturer of the
the following:
extensometer verified, or if it is an extensometer system
11.2.1 A statement indicating how, by whom, and when the
composed of separable components, the serial number and
most recent calibration of the apparatus used in verifying the
manufacturer of each component of the systems verified.
extensometer system was made.
11.1.4 gauge length of the extensometer. For variable gauge
11.2.2 A statement of the errors of the verification appara-
length extensometers, state the gauge lengths verifie
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E83 − 16 E83 − 23
Standard Practice for
Verification and Classification of Extensometer Systems
This standard is issued under the fixed designation E83; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope*
1.1 This practice covers procedures for the verification and classification of extensometer systems, but it is not intended to be a
complete purchase specification. The practice is applicable only to instruments that indicate or record values that are proportional
to changes in length corresponding to either tensile or compressive strain. Extensometer systems are classified on the basis of the
magnitude of their errors.
1.2 Because strain is a dimensionless quantity, this document can be used for extensometers based on either SI or US customary
units of displacement.
NOTE 1—Bonded resistance strain gauges directly bonded to a specimen cannot be calibrated or verified with the apparatus described in this practice for
the verification of extensometers having definite gauge points. (See procedures as described in Test Methods E251.)
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and healthsafety, health, and environmental practices and determine
the applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
E6 Terminology Relating to Methods of Mechanical Testing
E21 Test Methods for Elevated Temperature Tension Tests of Metallic Materials
E251 Test Methods for Performance Characteristics of Metallic Bonded Resistance Strain Gages
2.2 Other Standards:
JCGM 100:2008 Evaluation of measurement data – Guide to the expression of uncertainty in measurement
3. Terminology
3.1 Definitions:
This practice is under the jurisdiction of ASTM Committee E28 on Mechanical Testing and is the direct responsibility of Subcommittee E28.01 on Calibration of
Mechanical Testing Machines and Apparatus.
Current edition approved Dec. 15, 2016Jan. 1, 2023. Published January 2017February 2023. Originally approved in 1950. Last previous edition approved in 20102016
as E83 – 10a.E83 – 16. DOI: 10.1520/E0083-16.10.1520/E0083-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from International Organization for Standardization (ISO), ISO Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva,
Switzerland, http://www.iso.org.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E83 − 23
3.1.1 In addition to the terms listed, see Terminology E6.
3.1.2 calibration—a determination of the calibration factor for a system using established procedures.
3.1.3 calibration factor—the factor by which the change in extensometer reading must be multiplied to obtain the equivalent
strain.
3.1.3.1 Discussion—
For any extensometer, the calibration factor is equal to the ratio of change in length to the product of the gauge length and the
change in the extensometer reading. For direct-reading extensometers the calibration factor is unity.
3.1.4 compressometer—a specialized extensometer used for sensing negative or compressive strain.
3.1.5 deflectometer—a specialized extensometer used for sensing of extension or motion, usually without reference to a specific
gauge length.
3.1.6 dot/line tracking optical extensometer system (DLT), n—an optical extensometer system that uses marks at an initially known
distance, physically placed on a specimen or calibration fixture, to establish the gauge length value for determination of strain.
3.1.7 error, in extensometer systems—the value obtained by subtracting the correct value of the strain from the indicated value
given by the extensometer system.
3.1.8 extensometer, n—a device for sensing strain.
3.1.9 extensometer systems—a system for sensing and indicating strain.
3.1.9.1 Discussion—
The system will normally include an extensometer, conditioning electronics and auxiliary device (recorder, digital readout,
computer, etc.). However, completely self-contained mechanical devices are permitted. An extensometer system may be one of
three types.
3.1.10 Type 1 extensometer system, n—an extensometer system which both defines gauge length and senses extension, for
example, a clip-on strain gauge type with conditioning electronics.
3.1.11 Type 2 extensometer system, n—an extensometer which senses extension and the gauge length is defined by specimen
geometry or specimen features such as ridges or notches.
3.1.11.1 Discussion—
A Type 2 extensometer is used where the extensometer gauge length is determined by features on the specimen, for example,
ridges, notches, or overall height (in case of compression test piece). The precision associated with gauge length setting for a Type
2 extensometer should be specified in relevant test method or product standard. The position readout on a testing machine is not
recommended for use in a Type 2 extensometer system.
3.1.12 Type 3 extensometer system, n—an extensometer system which intrinsically senses strain (ratiometric principle), for
example, video camera system.
3.1.13 gauge length (L), n—the original length of that portion of the specimen over which strain or change of length is determined.
3.1.13.1 Discussion—
If the device is used for sensing extension or motion, and gauge length is predetermined by the specimen geometry or specific test
method, then only resolution and strain error for a specified gauge length should determine the class of extensometer system.
3.1.14 laser optical extensometer system, n—an optical extensometer system that uses a laser to track and measure the
extension/strain.
3.1.15 resolution of the strain indicator—the smallest change in strain that can be estimated or ascertained on the strain indicating
apparatus of the testing system, at any applied strain.
E83 − 23
3.1.16 resolution of the digital type strain indicators (numeric displays, printouts, and so forth)—the resolution is the smallest
change in strain that can be displayed on the strain indicator (may be a single digit or a combination of digits) at any applied strain.
3.1.16.1 Discussion—
If the strain indication, for either type of strain indicator, fluctuates more than twice the resolution, as described in 3.1.133.1.15
or 3.1.143.1.16, the resolution expressed as a strain shall be equal to one-half the range of fluctuation.
3.1.17 verification—a determination that a system meets the requirements of a given classification after calibration according to
established procedures.
3.1.18 verification apparatus—a device for verifying extensometer systems.
3.1.18.1 Discussion—
This device is used to simulate the change in length experienced by a test specimen as a result of the applied force. The
extensometer may either be attached directly to the mechanism or interfaced with it in a manner similar to normal operation (that
is, possibly without contact for some optical extensometers).
3.2 virtual optical extensometer system, n—an optical extensometer system in which the initial datum points used to establish the
gauge length value for determination of strain are chosen by the user based on a location in the image in software – the gauge length
is not defined by discrete marks on the specimen.
3.3 working distance, (WD), n—the physical distance that the optical extensometer system is from the surface of the specimen or
verification apparatus, the distance is measured from the front of the optical extensometer system.
3.3.1 Discussion—
The WD measurement can be made from the camera body to the front of the specimen or verification apparatus. While it is not
important where the physical distance is measured from it is important to measure the distance and report where the measurements
were made. Doing this will enable the user to recreate the conditions under which the optical extensometer system was verified.
4. Verification Apparatus
4.1 The apparatus for verifying extensometer systems shall provide a means for applying controlled displacements to a simulated
specimen and for measuring these displacements accurately. It may consist of a rigid frame, suitable coaxial spindles, or other
fixtures to accommodate the extensometer being verified, a mechanism for moving one spindle or fixture axially with respect to
the other, and a means for measuring accurately the change in length so produced, or any other device or mechanism that will
accomplish the purpose equally well. The mechanism provided for moving one spindle relative to the other shall permit sensitive
adjustments. The changes in length shall be measured, for example, by means of an interferometer, calibrated standard gauge
blocks and an indicator, a calibrated micrometer screw, or a calibrated laser measurement system. If standard gauge blocks and
an indicator, or a micrometer screw, are used, they shall be calibrated and their limits of accuracy and sensitivity stated. The errors
of the verification apparatus shall not exceed one third of the permissible error of the extensometer.
4.2 The verification apparatus shall be calibrated at intervals not to exceed two years.
NOTE 2—He-Ne laser interferometer measurement systems based on the 0.633 μm wavelength line are considered to be primary-based displacement
standards and do not require recalibration.
4.3 If the verification apparatus is to be used to verify extensometers used for bidirectional tests, the errors of the verification
apparatus should be measured in both directions of travel so as to include any backlash present.
5. Verification Procedure for Extensometer Systems
5.1 General Requirements—The verification of an extensometer system should not be done unless the components of the system
are in good working condition. Thoroughly inspect all parts associated with smooth operation of the instrument to ensure there are
no excessively worn components. Repair or replace parts as necessary. Remove any dirt particles which may have accumulated
A review of some past, current, and possible future methods for calibrating strain measuring devices is given in the paper by Watson, R. B., “Calibration Techniques
for Extensometry: Possible Standards of Strain Measurement,” Journal of Testing and Evaluation, JTEVA, Vol. 21, No. 6, November 1993, pp. 515–521.
A letter from NIST (National Institute of Standards and Technology) has been filed at ASTM International Headquarters and may be obtained by requesting Research
Report RR: E28-1013.
E83 − 23
through normal use of the instrument. Verification of the system shall be performed whenever parts are interchanged or replaced.
Some extensometers have parts that are designed to be interchanged such as gauge length extenders and lenses used with video
extensometers. If these parts can be shown to be interchangeable without degrading the verified classification of the extensometer,
they may be interchanged between scheduled verifications of the extensometer. Verification of the extensometer with all
combinations of interchangeable parts that are anticipated to be used for testing is required.
5.1.1 The verification of an extensometer system refers to a specific extensometer used with a specific readout device. Unless it
can be demonstrated that autographic extensometers and recorders of a given type may be used interchangeably without
introducing errors that would affect the classification of the extensometer, the extensometer shall be calibrated with the readout
device with which it is to be used.
5.1.2 Prior to the initial verification, the extensometer should be calibrated according to the manufacturer’s instructions or
established procedures. The calibration procedure may include adjustment of span or determination of calibration factor, or both.
5.2 Gauge Length Measurement Method—Measure the gauge length of self-setting instruments by either the direct or indirect
method.
NOTE 3—The following is an example of an indirect method. Set the extensometer to its starting position and mount it on a soft rod of the typical specimen
size or diameter. After the extensometer is removed, measure the distance between the marks left by the gauge points (or knife edges). If there are four
or more gauge points, take the average of the individual lengths as the gauge length. The differences between individual measurements shall not exceed
the tolerance given for the class of extensometer. If there are two gauge points (or knife edges), but on opposite sides of the specimen, attach the
extensometer twice rotating it 180° with respect to the rod. Take the average of the lengths thus established on each side of the rod as the gauge length.
5.2.1 Make two measurements of the gauge length. Determine and record the error from each measurement, which is the
difference between the measured gauge length and the specified gauge length, expressed as a percent of the specified gauge length.
5.2.2 For extensometer devices that do not have a self-setting gauge length during use, such as deflectometers and some
high-temperature tensile or creep extensometers, verification run errors should be calculated using the gauge length for which the
device is used. Separate classifications should be established for each gauge length or range used.
5.2.3 Some extensometers have the capability to measure the gauge length set by or chosen by the user. If this measurement is
used in the calculation of strain, then it is the inherent measurement accuracy that is the important factor rather than the error
between the chosen length and the actual.
NOTE 4—An example of an extensometer that is described by 5.2.3 is an optical extensometer that measures the position of “flags” attached to the test
specimen. The flags are positioned at the approximate required gauge length and the instrument measures the position of the flags (the actual gauge length)
before and after the specimen is stressed. Although this kind of device usually has a stated accuracy of gauge length, it must be verified by either direct
or indirect methods at the appropriate gauge lengths.
5.3 Position of Extensometer—Carefully position the extensometer on or interface it to the verification device in the same manner
as it is normally used for typical specimens. For extensometers that attach directly to the specimen, the verification device should
allow attachment to pieces that are similar to the specimen on which the extensometer will be attached.
5.4 Temperature Control—Verify the extensometer at approximately the same temperature at which it will be used. Allow
sufficient time for the verification device and extensometer to reach satisfactory temperature stability. Maintain temperature
stability by excluding drafts throughout the subsequent verification. Record the temperature during each verification run.
NOTE 5—Extensometers used for high-temperature testing may be verified at ambient temperature to insure proper operation, but fixtures should be
designed to verify performance at the actual test temperature. This is especially true with optical extensometers which may be adversely affected by air
density changes associated with thermal gradients and turbulence, environmental chamber windows, or specimen changes due to the environment. See
Appendix X2.
5.5 Method of Reading—Read the instrument or, in the case of an autographic extensometer, measure the record in the same
manner as during use.
5.5.1 For extensometer with dial micrometers or digital readouts, the readings shall be recorded. Extensometers that use
autographic methods shall have their charts read and recorded using a suitable measuring device, such as a vernier or dial caliper.
The use of an optical magnifying device is recommended when reading and measuring autographic records.
E83 − 23
NOTE 6—When autographic extensometer systems are used, care should be taken to minimize errors introduced by variances in the graph paper. These
errors can be due to dimensional changes from reproduction or humidity changes. Direct measurement of the trace soon after it was made eliminates the
graph paper errors and is desirable for systems verification.
NOTE 7—If an extensometer is equipped with a dial micrometer, it may be necessary to lightly tap the dial micrometer to minimize the effects of friction
and to ensure that the most stable and reproducible readings are obtained. If the dial micrometer is tapped during the verification procedure, include this
information in the report.
5.6 Zero Adjustment—After temperature stability has been achieved, displace the verification device (with extensometer in the test
position) to a slightly negative value and return to zero. If the reading does not return to zero, adjust and repeat the procedure until
the reading does return to zero.
5.7 Number of Readings—For any strain range, verify the extensometer system by applying at least five displacement values, not
including zero, at least two times, with the difference between any two successive displacement applications being no greater than
one-third the difference between the selected maximum and minimum displacements.
5.7.1 Extensometers need not be verified beyond the range over which they will be used. Multi-range (multi-magnification)
extensometers shall be verified for each range to be used.
NOTE 8—If the connection between the gauge points attached to the specimen and the indicating device is made through geared wheels or micrometer
screws, relatively large periodic errors may exist which might not be disclosed by this overall procedure. For such extensometers it may be necessary
to take additional readings within one turn of any geared wheel, micrometer screw, or the travel of one tooth of any meshing gear.
5.7.2 When it is desired to establish the range of an extensometer system designed to automatically select or extend ranges below
10 % of full scale without the influence of the operator, the number of readings shall depend on how many overlapping decades
are in the range. Extensometer readings should be chosen starting with the minimum reading and are grouped in overlapping
decades such that the maximum reading on one decade is the minimum on the next decade. There are to be at least five strain
applications per decade, unless the maximum, or the minimum strain on the range is reached before completing the decade. Strain
(displacements) in each decade are to be approximately 1:1, 2:1, 4:1, 7:1, and 10:1, starting with the minimum strain in each
decade.
5.7.2.1 In no case should the distance between two successive strains (displacements) within a decade differ by more than
one-third the difference between the minimum and maximum strains in that decade. Strains in the second successive run are to be
approximately the same as those of the first run. Report all percent values of accuracy, and report the indicator resolution at least
once per decade.
5.7.3 Lower Limit Criteria—as indicated in Table 1, all verified strain readings must have a resolution at least one-half the
allowable error, that is, the resolution is a limiting factor to determine a lower limit of the range. The lowest verified strain reading
must be at least 100 times the indicator resolution. Extensometer results used below the lowest verified strain reading may not
comply with the error limit specified by this standard practice.
NOTE 9—Example: For an extensometer with a gauge length of 1 in. and 50 % strain, the full scale displacement value is 0.5 in. If the machine (system)
resolution is 0.00005 in., which meets the criteria for the B1 class, the lower limit (verification range) would be 0.00005 in. x× 100 = 0.005 in., or 0.5
TABLE 1 Classification of Extensometer Systems
A B
Classification Relative Error of Resolution not to Exceed the Greater of: Error of Strain not to Exceed the Greater of:
gauge Length (max %)
(See 5.2)
Fixed Value % of Reading Fixed Error Relative Error
(in./in., m/m) (in./in., m/m) (% of strain)
Class A ±0.1 0.00001 0.05 ±0.00002 ±0.1
Class B-1 ±0.25 0.00005 0.25 ±0.0001 ±0.5
Class B-2 ±0.5 0.0001 0.25 ±0.0002 ±0.5
Class C ±1 0.0005 0.5 ±0.001 ±1
Class D ±1 0.005 0.5 ±0.01 ±1
Class E ±1 0.05 0.5 ±0.1 ±1
A
Class A classification is very difficult to achieve at short (1 in. (25 mm) or less) gauge lengths, so the commercial availability of an extensometer system that meets this
requirement may be very limited or nonexistent.
B
The strain of an Extensometer System is the ratio of applied extension to the gauge length.
E83 − 23
% strain. The suitable verification points for a single range extensometer system would be in percent strain 0.5, 1.0, 2.0, 3.5, 5, 10, 20, 35, and 50. (See
for single range system Fig. X1.1 and Fig. X1.2 for multirange.)
5.8 Number of Runs—Take at least two complete sets of extensometer readings for the same changes of length. After the first run,
an operation that simulates normal operation should be used to check repeatability. An extensometer that attaches directly to the
specimen should be removed and then reattached to the verification device between runs. An extensometer that does not attach
directly to the specimen should be moved away from the verification device (or the device moved away from the extensometer)
to simulate the changing of test specimens.
5.8.1 If the initial verification run (the “as found” run) produces satisfactory results which classify an extensometer system
according to Table 1 specifications, then the data may be used as run—one of the two required for the verification report.
5.8.2 If the initial verification run produces results which are outside of expectations, for example, Class C instead of B1, and
adjustments are necessary, then this first verification run might be reported “as found” data and used in accordance with applicable
quality control programs. Calibration adjustments may then be made to the extensometer system after which two required
verification runs shall be conducted and reported on the verification report and certificate.
5.8.3 The algebraic difference between errors of the two verification runs shall not exceed the required Classification criteria listed
in Table 1.
5.9 Direction of Verification Displacement:
5.9.1 Extensometers Used for Unidirectional Tests—Extensometers used for unidirectional tests (for example, tension tests) shall
be verified by applying displacement in the direction of testing normally used. If start-up backlash is evident, the verification device
(with extensometer in place) may be displaced to a slightly negative value and returned to zero before each run.
NOTE 10—This verification procedure does not measure the initial backlash in the extensometer that may appear after it is first attached to the specimen.
If the extensometer is used with open or closed loop-type test equipment in load control, the users should disregard readings taken during the initial part
of the loading curve. If the extensometer is used with closed loop test equipment in strain control, the backlash could result in large tension or compression
loads during the initial part of the loading curve.
5.9.2 Extensometers Used for Bidirectional Tests—Extensometers used for bidirectional tests (for example, hysteresis tests, fatigue
tests, and so forth) (See Appendix X3) shall be verified by applying both increasing and decreasing values of displacement over
the total range of intended use. Displace the verification device (with extensometer in place) to a slightly negative value and return
to zero before each run. During each run, displace the extensometer to the maximum positive value, then to the maximum negative
value, and then back to zero, stopping at each verification point along the way in each direction.
5.10 Determination of Errors—Calculate the error of the extensometer system for each change in length of the verification
apparatus. Errors are based on net values from the zero point to each successive verification point, not on increments between
verification points.
6. Classification of Extensometer Systems
6.1 Classify extensometer systems in accordance with the requirements as to maximum error of strain indicated by the
extensometer system shown in Table 1. The maximum allowable error in each class is the fixed error or the variable error,
whichever is greater. The fixed error will establish the maximum allowable error for readings near zero, but the variable error may
establish the maximum allowable error for readings near full scale. Two examples of this procedure are presented in Appendix X1.
In addition, the gauge length error for Type 1 extensometers shall not exceed the greater of the values shown in Table 1.
6.1.1 Type 2 extensometer systems shall be classified using the smallest gauge length for which they are used. They may be
verified at additional gauge lengths if desired.
6.1.2 Type 3 extensometer systems, operating over a range of gauge lengths, shall be verified at the minimum and maximum gauge
lengths used. They may be verified at additional gauge lengths if desired.
NOTE 11—For Type 3 systems, precision marked, divided test pieces may be used to establish known gauge lengths on the calibration device. Known
extensions enable the applied strains to be set. These applied strains are compared with the indicated strains from the Type 3 extensometer systems, in
order to establish its classification in accordance with the requirements for resolution and strain error in Table 1.
E83 − 23
6.2 Separate classifications may be established for different ranges of multi-range (multiple-magnification) extensometer systems.
7. Verification of Multiple Strain Readouts
7.1 When an extensometer is to be used with two or more readout devices (for example, a graphic recorder and a digital readout),
steps must be taken to assure that errors are not introduced by interactions (mechanical or electrical) between the readout devices
or between the readouts and the extensometer, and that values from each readout device satisfy appropriate performance criteria.
(Different accuracy classifications could be given to the systems using different readout devices.) This can best be accomplished
by verifying each system (extensometer and readout device) individually and also in combinations that would be used
simultaneously. As an alternative, after individual verifications have been made, the combination can be checked at three points
(about 20, 50,20 %, 50 %, and 90 % of full scale range are recommended); and, if values for each system do not differ from the
individual verification values by more than 20 % of the class tolerance, the combined system shall be considered to meet the same
requirements as the individual systems. If readout devices are always used in combination, individual verifications are not required
when the combined system is verified as a unit.
8. Verification of Data Acquisition Systems
8.1 Extensometer systems in which strain values are indicated on displays or printouts of data acquisition systems, be they
instantaneous, delayed, stored or retransmitted, which are verified in accordance with the provisions of Section 55 and classified
in accordance with the provisions of Section 66,, shall be deemed to comply with this practice.
9. Time Interval Between Verifications
9.1 It is recommended that extensometer systems be verified annually unless more frequent verification is required to comply with
product or customer specifications. In no case shall the time interval between verifications exceed 18 months unless an
extensometer is being used on a long-time test running beyond the 18-month period. In such cases, the extensometer system shall
be verified immediately after completion of the test. (See Note 12.)
9.1.1 An extensometer system shall not be used after an adjustment or repair that could affect its accuracy without first verifying
its accuracy utilizing the procedure described in this practice.
NOTE 12—If a test is expected to last more than 18 months, it is recommended that the extensometer system be verified immediately before as well as
upon completion of the test.
10. Accuracy Assurance Between Verifications
10.1 Some product-testing procedures may require daily, weekly, or monthly spot checks to ascertain that an extensometer,
recorder, or display, and so forth, or combinations thereof etc., are capable of producing accurate strain values between the
verifications specified in Section 9. Spot checks may be performed on ranges of interest or at strain levels of interest utilizing a
verification device that complies with Section 44 for the strain level(s) at which the spot checks are made.
10.2 Check the extensometer gauge length (see 5.1).
10.3 Make spot checks of extensometer readings at approximately 1010 % and 50 % of a range unless otherwise agreed upon or
stipulated by the material supplier or user.
10.4 The extensometer gauge length and strain measurement errors shall not exceed the allowable errors at the spot check points
for the specified class of extensometer. Should errors be greater than allowable at any of the spot check points, the extensometer
system is to be completely verified immediately.
10.5 When spot checks are made, a clear, concise record must be maintained as agreed upon between the supplier and the user.
The record shall contain gauge length and spot check test data; the name, serial number, verification date, verification agency of
the verification device(s) used to make spot checks; the name of person making the spot check; and documentation of the regular
verification data and schedule.
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10.6 The extensometer system shall be considered verified up to the date of the last successful spot check verification provided
that the extensometer system is verified in accordance with Section 55 on a regular schedule in accordance with Section 99.
Otherwise, spot checks are not valid.
11. Report
11.1 The report shall include the following:
11.1.1 Method of gauge length verification used.
11.1.2 Serial numbers and names of the manufacturers of all apparatus used in verifying the extensometer system.
11.1.3 Serial number and name of the manufacturer of the extensometer verified, or if it is an extensometer system composed of
separable components, the serial number and manufacturer of each component of the systems verified.
11.1.4 gauge length of the extensometer. For variable gauge length extensometers, state the gauge lengths verified.
11.1.5 Temperature of the extensometer during verification.
11.1.6 Complete record of the readings of the extensometer and of the verification apparatus.
11.1.7 Calibration factor, if applicable.
11.1.8 Error in gauge length for each measurement of gauge length.
11.1.9 Error and relative error of the extensometer for each extensometer reading, the maximum algebraic error difference
(repeatability) and the associated resolution for each range (decade).
11.1.10 Class of the extensometer system. If separate classifications are established for various ranges, report the range (or
magnification) and strain values associated with each classification.
11.1.11 If the classification applies to bidirectional testing, it shall be so stated. Otherwise, the classification shall be considered
to be unidirectional in the direction of normal use (that is, opening for tension testing, closing for compression testing, and so
forth).
11.1.12 The name of the person performing the classification and the date it was performed.
11.2 Information to be available upon request shall include the following:
11.2.1 A statement indicating how, by whom, and when the most recent calibration of the apparatus
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