ASTM E251-20

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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: E251 − 92 (Reapproved 2014) E251 − 20
Standard Test Methods for
Performance Characteristics of Metallic Bonded Resistance
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Strain Gages
This standard is issued under the fixed designation E251; 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.
INTRODUCTION
The Organization of International Legal Metrology is a treaty organization with approximately 75
member nations. In 1984, OIML issued International Recommendation No. 62, “Performance
Characteristics of Metallic Resistance Strain Gages.” Test Methods E251 has been modified and
expanded to be the United States of America’s compliant test specification. Throughout this standard
the terms “strain gage” and “gage” are to be understood to represent the longer, but more accurate,
“metallic bonded resistance strain gages.”
1. Scope
1.1 The purpose of these test methods are to provide uniform test methods for the determination of strain gage performance
characteristics. Suggested testing equipment designs are included.
1.2 Test Methods E251 describes methods and procedures for determining five strain gage parameters:
Section
Part I—General Requirements 7
Part II—Resistance at a Reference Temperature 8
Part III—Gage Factor at a Reference Temperature 9
Part IV—Temperature Coefficient of Gage Factor 10
Part V—Transverse Sensitivity 11
Part VI—Thermal Output 12
1.3 Strain gages are very sensitive devices with essentially infinite resolution. Their response to strain, however, is low and great
care must be exercised in their use. The performance characteristics identified by these test methods must be known to an
acceptable accuracy to obtain meaningful results in field applications.
1.3.1 Strain gage resistance is used to balance instrumentation circuits and to provide a reference value for measurements since
all data are related to a change in the gage resistance from a known reference value.
1.3.2 Gage factor is the transfer function of a strain gage. It relates resistance change in the gage and strain to which it is
subjected. Accuracy of strain gage data can be no better than the precision of the gage factor.
1.3.3 Changes in gage factor as temperature varies also affect accuracy although to a much lesser degree since variations are
usually small.
1.3.4 Transverse sensitivity is a measure of the strain gage’s response to strains perpendicular to its measurement axis. Although
transverse sensitivity is usually much less than 10 % of the gage factor, large errors can occur if the value is not known with
reasonable precision.
1.3.5 Thermal output is the response of a strain gage to temperature changes. Thermal output is an additive (not multiplicative)
error. Therefore, it can often be much larger than the gage output from structural loading. To correct for these effects, thermal
output must be determined from gages bonded to specimens of the same material on which the tests are to run, often to the test
structure itself.
1.4 Bonded resistance strain gages differ from extensometers in that they measure average unit elongation (ΔL/L) over a
nominal gage length rather than total elongation between definite gauge points. Practice E83 is not applicable to these gages.
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These test methods are under the jurisdiction of ASTM Committee E28 on Mechanical Testing and are the direct responsibility of Subcommittee E28.01 on Calibration
of Mechanical Testing Machines and Apparatus.
Current edition approved April 15, 2014May 1, 2020. Published August 2014August 2020. Originally approved in 1964. Last previous edition approved in 20092014 as
E251 – 92 (2009).(2014). DOI: 10.1520/E0251-92R14.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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E251 − 20
1.5 These test methods do not apply to transducers, such as load cells and extensometers, that use bonded resistance strain gages
as sensing elements.
1.6 strainStrain gages are part of a complex system that includes structure, adhesive, gage, lead wires, instrumentation, and
(often) environmental protection. As a result, many things affect the performance of strain gages, including user technique. A
further complication is that strain g
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