ASTM E898-20

Standard Practice for Calibration of Non-Automatic Weighing Instruments

SIGNIFICANCE AND USE
4.1 This practice will enable calibration laboratories and the user to calibrate electronic non-automatic weighing instruments and quantify the error of the balance throughout the measurement range, usually from zero to maximum capacity. The error of indication is accompanied by a statement on measurement uncertainty, which is individually estimated for every measurement point. This practice is based on the test procedures and uncertainty estimation described in the EURAMET calibration guide cg-18. However, while EURAMET cg-18 allows for a very flexible execution of the measurements, the test procedures described in this practice are more fixed to enable a better comparability between calibrations executed by different calibration laboratories or users. This practice may also serve as basis for accreditation of calibration laboratories for calibration of electronic non-automatic weighing instruments.  
4.2 This practice allows the user to decide whether the calibrated balance is fit for its intended purpose, based on the assessment of the calibration results. Usually, this assessment is done by ensuring that the measurement uncertainty of all weighings the user performs on the instrument is smaller than a specified relative tolerance established by the user. This approach is commensurate to assuring that the smallest net amount of substance that the user weighs on the instrument (so-called smallest net weight) is larger than the minimum weight, which is derived from the calibration results.  
4.3 This practice, in Appendix X2, provides information on the periodic performance verification on the balance that should be carried out by the user between the calibrations. Calibration together with periodic performance verification allows the user to ensure with a very high degree of probability that the balance meets the user requirements during its day-to-day usage. It helps users comply with requirements from other standards or regulations that stipulate periodic test...
SCOPE
1.1 This practice applies to the calibration of electronic non-automatic weighing instruments. A non-automatic weighing instrument is a measuring instrument that determines the mass of an object by measuring the gravitational force acting on the object. It requires the intervention of an operator during the weighing process to decide whether the weighing result is acceptable.  
1.2 Non-automatic weighing instruments have capacities from a few grams up to several thousand kilograms, with a scale interval typically from 0.1 micrograms up to 1 kilogram. Note that non-automatic weighing instruments are usually referred to as either balances or scales. In this practice, for brevity, non-automatic weighing instruments will be referred to as balances; however, the scope of this practice also includes scales.  
1.3 This practice only covers electronic non-automatic weighing instruments where the indication is obtained from a digital display. The measuring principle is usually based on the force compensation principle. This principle is realized either by elastic deformation, where the gravitational force of the object being weighed is measured by a strain gauge that converts the deformation into electrical resistance, or by electromagnetic force compensation, where the gravitational force is compensated for by an electromagnetic counterforce that holds the load cell in equilibrium.  
1.4 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.5 This standard does not purport to be suitable as the sole testing process for weighing systems designated for commercial service under weights and measures regulation. The legal requirements for such instruments vary from region to region, and also depend on specific applications. To determine applicable legal requirements, contact the weights and measures authority in the region where the device is located. ...

General Information

• Status: Published
• Publication Date: 30-Apr-2020
• ICS: 17.100 - Measurement of force, weight and pressure
• Technical Committee: E41 - Laboratory Apparatus
• Drafting Committee: E41.06 - Laboratory Instruments and Equipment

Relations

• Replaces: ASTM E898-88(2013) - Standard Test Method of Testing Top-Loading, Direct-Reading Laboratory Scales and Balances
• Effective Date: 01-May-2020
• Refers: ASTM E617-23 - Standard Specification for Laboratory Weights and Precision Mass Standards
• Effective Date: 15-Aug-2023
• Refers: ASTM E617-18 - Standard Specification for Laboratory Weights and Precision Mass Standards
• Effective Date: 01-Oct-2018
• Refers: ASTM E617-97(2008) - Standard Specification for Laboratory Weights And Precision Mass Standards
• Effective Date: 01-Dec-2008
• Refers: ASTM E617-97(2003) - Standard Specification for Laboratory Weights And Precision Mass Standards
• Effective Date: 10-Nov-1997
• Refers: ASTM E617-97 - Standard Specification for Laboratory Weights And Precision Mass Standards
• Effective Date: 10-Nov-1997
• Referred By: ASTM D5907-18 - Standard Test Methods for Filterable Matter (Total Dissolved Solids) and Nonfilterable Matter (Total Suspended Solids) in Water
• Effective Date: 01-May-2020
• Referred By: ASTM E542-22 - Standard Practice for Gravimetric Calibration of Laboratory Volumetric Instruments
• Effective Date: 01-May-2020
• Referred By: ASTM E1154-23 - Standard Specification for Piston or Plunger Operated Volumetric Apparatus and Operator Qualification
• Effective Date: 01-May-2020
• Referred By: ASTM D7542-21 - Standard Test Method for Air Oxidation of Carbon and Graphite in the Kinetic Regime
• Effective Date: 01-May-2020
• Referred By: ASTM D6489-99(2020) - Standard Test Method for Determining the Water Absorption of Hardened Concrete Treated With a Water Repellent Coating
• Effective Date: 01-May-2020
• Referred By: ASTM D7578-20 - Standard Guide for Calibration Requirements for Elemental Analysis of Petroleum Products and Lubricants
• Effective Date: 01-May-2020
• Referred By: ASTM D8293-22 - Standard Guide for Evaluating and Expressing the Uncertainty of Radiochemical Measurements
• Effective Date: 01-May-2020

Overview

ASTM E898-20: Standard Practice for Calibration of Non-Automatic Weighing Instruments provides a consistent procedure for calibrating electronic non-automatic weighing instruments, commonly referred to as balances or scales. Issued by ASTM International, this standard addresses the needs of calibration laboratories and end users by outlining precise methods to determine and quantify errors in balance indication over the full measurement range, from zero to maximum capacity. The standard emphasizes the importance of measurement uncertainty, offering detailed guidance to ensure calibrated instruments meet user and regulatory requirements.

Calibration in accordance with ASTM E898-20 is essential for maintaining measurement accuracy and reliability in environments where precise weighing is critical, such as laboratories, industrial settings, and quality management systems. The practice is designed to be harmonized with international guidance, notably EURAMET cg-18, but prescribes more fixed procedures to improve reproducibility among different laboratories and users.

Key Topics

• Calibration Scope: Covers electronic non-automatic weighing instruments with digital displays, using principles such as force compensation (e.g., strain gauge or electromagnetic counterforce).
• Measurement Range: Applies to balances with capacities from several grams to several thousand kilograms, with scale intervals as fine as 0.1 micrograms.
• Calibration Parameters: Assesses repeatability, eccentric loading error, and indication error across the balance’s usable range.
• Measurement Uncertainty: Each calibration point’s error of indication is accompanied by an estimated measurement uncertainty, ensuring traceability and confidence in weighing results.
• Use of Standard Weights: Requires the use of traceable standard weights meeting specified requirements (e.g., OIML R111-1 or ASTM E617).
• Environmental and Procedural Conditions: Calls for stable environmental conditions and proper acclimatization of weights and instruments before calibration.
• Performance Verification: Includes guidance on periodic performance checks between calibrations to ensure ongoing compliance.
• Compliance and Accreditation: Can be used as an accreditation basis for calibration laboratories and helps organizations comply with ISO/IEC 17025 and other regulatory frameworks.

Applications

ASTM E898-20 finds practical application across various fields where accurate mass determination is vital:

• Laboratory Calibration: Used by metrology and calibration laboratories for routine and initial calibration of analytical and precision balances.
• Quality Control: Supports manufacturing, pharmaceutical, and food industries in meeting quality assurance requirements for weighing accuracy and traceability.
• Regulatory Compliance: Assists in meeting global requirements for measurement traceability and uncertainty in accordance with ISO 9001, ISO/IEC 17025, and other standards.
• Accreditation Readiness: Provides a methodology that is widely accepted by accreditation bodies for demonstrating competency in balance calibration.
• Routine Verification: Offers a framework for in-house periodic verification, promoting ongoing instrument reliability and supporting compliance with good manufacturing practices (GMP) and good laboratory practices (GLP).

With this standard, organizations can confidently assess if their balances are fit for intended use, based on quantitative calibration results and well-defined uncertainty tolerances.

Related Standards

For enhanced traceability and compliance, ASTM E898-20 references and aligns with several key standards and guides:

• ASTM E617 – Specification for Laboratory Weights and Precision Mass Standards
• ISO/IEC 17025 – General Requirements for the Competence of Testing and Calibration Laboratories
• ISO 9001 – Quality Management Systems Requirements
• OIML R76-1 – Non-Automatic Weighing Instruments: Metrological and Technical Requirements
• OIML R111-1 – Weights of Classes E1, E2, F1, F2, M1, M2, and M3
• EURAMET cg-18 – Guidelines on the Calibration of Non-Automatic Weighing Instruments
• USP General Chapters 41 and 1251 – Balances and Analytical Balance Weighing
• JCGM 100 – Guide to the Expression of Uncertainty in Measurement (GUM)

Adhering to ASTM E898-20 ensures that electronic non-automatic weighing instruments are calibrated in a manner that is internationally recognized, supports accurate mass measurement, and fulfills critical quality and compliance needs.

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: E898 − 20
Standard Practice for
Calibration of Non-Automatic Weighing Instruments
This standard is issued under the fixed designation E898; 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.
1. Scope 1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This practice applies to the calibration of electronic
responsibility of the user of this standard to establish appro-
non-automatic weighing instruments. A non-automatic weigh-
priate safety, health, and environmental practices and deter-
ing instrument is a measuring instrument that determines the
mine the applicability of regulatory limitations prior to use.
mass of an object by measuring the gravitational force acting
1.7 This international standard was developed in accor-
on the object. It requires the intervention of an operator during
dance with internationally recognized principles on standard-
the weighing process to decide whether the weighing result is
ization established in the Decision on Principles for the
acceptable.
Development of International Standards, Guides and Recom-
1.2 Non-automatic weighing instruments have capacities
mendations issued by the World Trade Organization Technical
from a few grams up to several thousand kilograms, with a
Barriers to Trade (TBT) Committee.
scale interval typically from 0.1 micrograms up to 1 kilogram.
Note that non-automatic weighing instruments are usually
2. Referenced Documents
referred to as either balances or scales. In this practice, for 2
2.1 ASTM Standards:
brevity,non-automaticweighinginstrumentswillbereferredto
E617 Specification for Laboratory Weights and Precision
as balances; however, the scope of this practice also includes
Mass Standards
scales.
2.2 ISO Standards:
1.3 This practice only covers electronic non-automatic
ISO 9001 Quality Management Systems – Requirements
weighing instruments where the indication is obtained from a
ISO/IEC 17025 General Requirements for the Competence
digital display.The measuring principle is usually based on the
of Testing and Calibration Laboratories
force compensation principle. This principle is realized either
2.3 OIML Documents and Recommendations:
by elastic deformation, where the gravitational force of the
D28 Conventional Value of the Result of Weighing in Air
object being weighed is measured by a strain gauge that
R76-1 Non-automatic Weighing Instruments – Part 1: Met-
converts the deformation into electrical resistance, or by
rological and Technical Requirements – Tests
electromagnetic force compensation, where the gravitational
R111-1 Weights of classes E ,E ,F ,F ,M ,M ,M and
1 2 1 2 1-2 2 2-3
force is compensated for by an electromagnetic counterforce
M – Part 1: Metrological and Technical Requirements
that holds the load cell in equilibrium.
2.4 EURAMET Guide:
Calibration Guide No. 18 Guidelines on the Calibration of
1.4 Units—The values stated in SI units are to be regarded
Non-automatic Weighing Instruments
as standard. No other units of measurement are included in this
standard. 2.5 JCGM Guides:
JCGM 100 Evaluation of Measurement Data – Guide to the
1.5 This standard does not purport to be suitable as the sole
Expression of Uncertainty in Measurement (GUM)
testing process for weighing systems designated for commer-
cial service under weights and measures regulation. The legal
requirements for such instruments vary from region to region, 2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
and also depend on specific applications. To determine appli-
Standards volume information, refer to the standard’s Document Summary page on
cable legal requirements, contact the weights and measures
the ASTM website.
authority in the region where the device is located.
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.
1 4
This practice is under the jurisdiction ofASTM Committee E41 on Laboratory Available from the Organisation Internationale de Métrologie Légale (OIML),
Apparatus and is the direct responsibility of Subcommittee E41.06 on Laboratory 11 Rue Turgot, 75009 Paris, France, https://www.oiml.org/en.
Instruments and Equipment. Available from EURAMET e.V., Bundesallee 100, 38116 Braunschweig,
Current edition approved May 1, 2020. Published June 2020. Originally Germany, https://www.euramet.org.
approvedin1982.Lastpreviouseditionapprovedin2013asE898 – 88(2013).DOI: Available from the Bureau International des Poids et Mesures, Pavillon de
10.1520/E0898-20. Breteuil, 92312 Sèvres, France, https://www.bipm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E898 − 20
JCGM 200 International Vocabulary of Metrology – Basic 3.1.4 conventional mass value, n—mass value indicated in
and General Concepts and Associated Terms (VIM) the calibration certificate of the weight.
3.1.4.1 Discussion—The conventional mass value of a body
2.6 ILAC Guideline:
is equal to the mass of a standard that balances this body under
ILAC-G24 Guidelines for the Determination of Calibration
conventionally chosen conditions, that is, at 20 °C, a density of
Intervals of Measuring Instruments, ILAC-G24
3 3 14
8 the standard of 8000 kg⁄m in air of density 1.2 kg⁄m .
2.7 USP General Chapters:
3.1.5 coverage factor (k), n—number larger than one by
USP General Chapter 41 Balances
which a combined standard measurement uncertainty is mul-
USP General Chapter 1251 Weighing on an Analytical
tiplied to obtain an expanded measurement uncertainty.
Balance
3.1.5.1 Discussion—The coverage factor (k) is typically
2.8 UKAS Guide:
calculated based on the applicable degrees of freedom (ν).
UKAS LAB 14, Edition 5 In-house Calibration and Use of
Weighing Machines 3.1.6 eccentric loading error, n—error when the load is not
placed in the center of the weighing platform.
2.9 Code of Federal Regulations:
3.1.6.1 Discussion—The deviation in the measurement
CFR Part 58 Good Laboratory Practice for Nonclinical
value caused by asymmetrical placement of the center of
Laboratory Studies
gravity of the load relative to the load receptor.
CFR Part 211 Current Good Manufacturing Practice for
Finished Pharmaceuticals 3.1.7 error, n—difference between the indicated quantity
and the applied quantity.
2.10 FDA Guidance:
3.1.7.1 Discussion—Error is the measured quantity value
FDAQuestions andAnswers on Current Good Manufactur-
minus a reference quantity value.
ingPractices,GoodGuidancePractices,Level2Guidance
– Equipment
3.1.8 linearity, n—abilityofaweighinginstrumenttofollow
For dated references, only the dated version applies to this the linear relationship between a load and the indication.
practice. For undated references, the latest edition (including
3.1.9 maximum capacity, n—maximum weighing capacity,
all amendments) applies to this practice.
thatis,themaximumcapacitywhoseweightcanbedetermined
on a balance.
3. Terminology
3.1.10 maximum permissible error (mpe), n—limitbywhich
3.1 Definitions of Terms Specific to This Standard:
the measured quantity indication can deviate from the nominal
3.1.1 In this section, the official definitions of the terms are
applied value.
provided, as are, where appropriate, simplified definitions that
3.1.10.1 Discussion—The extreme value of measurement
relate the terms to the scope of this practice.
error, with respect to a known reference quantity value,
3.1.2 accuracy class of weights, n—class designation of a
permitted by specifications or regulations for a given
weight or weight set which meets certain metrological require- 13
measurement, measuring instrument, or measuring system.
ments intended to maintain the mass values within specified
3.1.11 measurement standard, n—realization of the defini-
limits.
tion of a given quantity, with stated quantity value and
3.1.3 calibration, n—operation that establishes a relation
associated measurement uncertainty, used as a reference.
between the indication of the weighing instrument and the
3.1.12 measurement uncertainty, n—parameter that quanti-
reference weights, including the associated measurement un-
fies how far a measurement value might be away from the true
certainties.
(unknown) value.
3.1.3.1 Discussion—An operation that, under specified
3.1.12.1 Discussion—The non-negative parameter charac-
conditions, in a first step, establishes a relation between the
terizingthedispersionofthequantityvaluesbeingattributedto
quantity values with measurement uncertainties provided by
a measurand, based on the information used.
measurement standards and corresponding indications with
3.1.13 minimum weight, n—smallest sample weight re-
associated measurement uncertainties and, in a second step,
quired for a weighment to just achieve a specified relative
uses this information to establish a relation for obtaining a
accuracy of weighing.
measurement result from an indication.
3.1.14 nominal capacity, n—nominal value of the weighing
capacity, derived from the maximum capacity by rounding it
7 15
Available from the International Laboratory Accreditation Cooperation, ILAC
down to a number with less significant digits.
Secretariat, PO Box 7507, Silverwater NSW 2128, Australia, https://ilac.org.
3.1.15 repeatability, n—ability of a weighing instrument to
Available from U.S. Pharmacopeial Convention (USP), 12601 Twinbrook
Pkwy., Rockville, MD 20852-1790, http://www.usp.org.
provide indications that are close together when weighing the
Available from the United Kingdom Accreditation Service (UKAS), 2 Pine
same object several times under reasonably constant test
Trees, Chertsey Lane, Staines-upon-Thames, TW18 3HR, UK, https://
conditions.
www.ukas.com.
Available from the United States Federal Register, https://www.archives.gov/
federal-register.
11 14
Available from U.S. Food and Drug Administration (FDA), 10903 New Definition from OIML D28.
Hampshire Ave., Silver Spring, MD 20993, http://www.fda.gov. Nater, R., Reichmuth, A., Schwartz, R., Borys, M., and Panagiotis, Z.,
Definition from OIML R111-1. Dictionary of Weighing Terms, Springer, ISBN 978-3-642-02013-1, 2009.
13 16
Definition from JCGM 200 (VIM). Definition from OIML R76-1.
E898 − 20
3.1.15.1 Discussion—The ability of an instrument to pro-
rep repeatability
0 no load
vide results that agree one with the other when the same load
is deposited several times and in a practically identical way on
4. Significance and Use
the load receptor under reasonably constant test conditions.
4.1 This practice will enable calibration laboratories and the
3.1.16 scale interval, n—the difference between two con-
user to calibrate electronic non-automatic weighing instru-
secutive indicated values.
ments and quantify the error of the balance throughout the
3.1.17 sensitivity, n—change in indication divided by
measurement range, usually from zero to maximum capacity.
change in the applied quantity. The error of indication is accompanied by a statement on
3.1.17.1 Discussion—The quotient of the change in an
measurement uncertainty, which is individually estimated for
indicationofameasuringsystemandthecorrespondingchange every measurement point. This practice is based on the test
in a value of a quantity being measured.
procedures and uncertainty estimation described in the
EURAMET calibration guide cg-18. However, while
3.2 Symbols:
EURAMET cg-18 allows for a very flexible execution of the
d—scale interval
measurements,thetestproceduresdescribedinthispracticeare
D—drift, value change with time
more fixed to enable a better comparability between calibra-
d —smallest scale interval
tions executed by different calibration laboratories or users.
E—error of indication
This practice may also serve as basis for accreditation of
I —indication
calibration laboratories for calibration of electronic non-
k—coverage factor
automatic weighing instruments.
L—load
m —object mass 4.2 This practice allows the user to decide whether the
calibrated balance is fit for its intended purpose, based on the
Max—maximum capacity
assessment of the calibration results. Usually, this assessment
Max —upper limit of partial weighing range with smallest
is done by ensuring that the measurement uncertainty of all
scale interval
weighings the user performs on the instrument is smaller than
m —conventional value of mass
c
a specified relative tolerance established by the user. This
m —minimum weight
min
approach is commensurate to assuring that the smallest net
m —nominal mass
N
amount of substance that the user weighs on the instrument
mpe—maximum permissible error of a measured quantity
(so-called smallest net weight) is larger than the minimum
m —reference mass
ref
weight, which is derived from the calibration results.
n—number of repeated weighings
R—reading
4.3 This practice, in Appendix X2, provides information on
s—standard deviation
the periodic performance verification on the balance that
SF—safety factor
should be carried out by the user between the calibrations.
T—temperature (unit K)
Calibration together with periodic performance verification
u—standard uncertainty
allows the user to ensure with a very high degree of probability
U—expanded uncertainty
that the balance meets the user requirements during its day-to-
u —combined standard uncertainty day usage. It helps users comply with requirements from other
c
α—intercept (for uncertainty in use) standards or regulations that stipulate periodic tests and cali-
β—slope (for uncertainty in use) brations of quality-relevant instruments.
ν—degrees of freedom
5. Calibration Conditions
ν —effective degrees of freedom for combined standard
eff
5.1 Standard Weights
uncertainty
5.1.1 General Requirements—Test loads shall consist of
ρ—density
standard weights that are traceable to the SI unit of mass, with
ρ —reference density of air, ρ = 1.2 kg/m
0 0
the possible exception of test loads used for measurements of
ρ —reference density of mass, ρ = 8000 kg/m
c c
a comparative nature—for example, measurement of eccentric
ρ —density of standard weights
S
loading or repeatability.
3.3 Symbol Subscripts and Definitions
5.1.2 Standard Weight Traceability—The traceability of
Subscript Related
weights to be used as standards shall be demonstrated by
calibration consisting of:
B air buoyancy
conv convection 5.1.2.1 Determination of the conventional value of mass m
c
D drift
or the correction δm to its nominal value m :δm 5m 2m ,or
N c c N
c
L load
both, together with the expanded uncertainty of the calibration
N nominal value
dig digitization U,or
ecc load in different locations on the
5.1.2.2 Confirmation that m is within specified maximum
weighing pan
c
i, j number
permissible errors mpe: m 2 mpe2U #m #m 1 mpe2U .
~ ! ~ !
N c N
max maximum
min minimum 5.1.2.3 The standards should further satisfy the following
ref reference
requirements to an extent appropriate to their accuracy:
E898 − 20
kg
tion. Non-acclimatized weights trigger a convection effect of
(1) Density ρ sufficiently close to ρ 58000 ,
s c 3
m
the surrounding air that may impact the indication of the
(2) Surface finish suitable to prevent a change in mass
balance. Information on acclimatization times may be found,
through contamination by dirt or adhesion layers, and
for example, in EURAMET cg-18, Specification E617,or
(3) Magnetic properties such that interaction with the
OIML R111-1.
instrument to be calibrated is minimized.
5.1.2.4 Weights that comply with the relevant specifications 6. Calibration Practice
of OIMLR111-1 or Specification E617 should satisfy all these
6.1 Measurement Parameters General—This practice in-
requirements.
cludes the following measurement parameters:
5.1.3 Recommendation for the Selection of Weight
Repeatability;
Classes—It is recommended selecting the weights in order to
Eccentric loading; and
minimize their uncertainty contribution to the balance uncer-
Error of indication.
tainty as far as reasonably possible so that user tolerance
6.1.1 These three measurements may be performed in any
requirements are met. The following selection criteria for
order to accommodate efficient usage of weights and detect
weight classes could be considered:
potential defects of the weighing instrument at an early stage.
5.1.3.1 1 000 000 < Max/d: Select an OIML E or ASTM
6.2 Calibration
Class 1 weight, or a weight with uncertainty not worse than the
6.2.1 Calibration Range—The calibration range is typically
permitted OIML E or ASTM Class 1 uncertainty, which is
from the zero point of the balance to maximum capacity, or the
one-third or less of the maximum permissible error; it is
weighing range specified by the customer.
recommendedtoalwaysusetheconventionalmassvalueasthe
6.2.2 Calibration Location—Calibration shall be performed
reference value;
at the location of use of the balance. If calibration at the
5.1.3.2 150 000 < Max/d ≤ 1 000 000: For a weight where
location of use is not possible, then this exception shall be
the nominal value is used as the reference value, select an
noted in the calibration certificate. If the balance is moved to
OIMLF orASTMClass2weightorbetter;foraweightwhere
another location after calibration, the following situations may
the conventional mass value is used as the reference value,
occur:
select an OIML F or ASTM Class 4 weight or better;
(1) Difference in local gravitational acceleration;
5.1.3.3 15 000 < Max/d ≤ 150 000: For a weight where the
(2) Changes in environmental conditions; and
nominal value is used as the reference value, select an OIML
(3) Impact (damage) during transport.
F or ASTM Class 4 weight or better; for a weight where the
conventional mass value is used as the reference value, select NOTE 1—Each of the above may cause the performance of the balance
to change and can invalidate the calibration. Therefore, moving the
an OIML M or ASTM Class 5 weight or better; and
balance after calibration should be avoided. Recalibration of the balance
5.1.3.4 Max/d ≤ 15 000: For a weight where the nominal
is recommended after it has been moved if evidence of altered perfor-
value is used as the reference value, select an OIML M or
mance cannot be excluded.
ASTM Class 5 weight or better; for a weight where the
6.2.3 Preparation Before Calibration—Check the balance
conventional mass value is used as the reference value, select
nameplate or product identification. Identify the model, scale
an OIML M or ASTM Class 6 weight or better.
interval, maximum capacity, serial number, manufacturer, and
5.1.3.5 For multi-interval and multiple range balances, Max
other applicable information. The balance shall be energized at
and drefertotheinterval/rangewiththesmallestscaleinterval,
an appropriate time prior to calibration, such as the warm-up
abbreviated as Max and d , respectively.
1 1
time specified in the balance instructions or the time set by the
5.2 Substitution Loads
user.
5.2.1 Calibration requiring substitution loads is not within
6.2.3.1 If there is no such rule, the balance warm-up time
the scope of this practice. Substitution is discussed elsewhere should be no less than 30 min.
(see EURAMET cg-18).
6.2.3.2 If as-found data is to be collected, do not level prior
to as-found calibration. The balance should be levelled before
5.3 Other Measuring Instruments Used for Calibration
as-left calibration.
5.3.1 Thermometer for monitoring air temperature with a
6.2.3.3 If the balance is equipped with an auto-zero
resolution of 0.5 °C or better.
function, this function should be turned off before calibration,
5.3.2 Hygrometer for monitoring ambient relative humidity
if possible.
with a resolution of 5 % RH or better.
6.2.4 Measurement of Repeatability—Under repeatability
5.4 Calibration Environmental Conditions
conditions, the same load is placed on the balance pan several
5.4.1 Environmental temperature and relative humidity
times in a practical and consistent manner in a short time
shall be recorded and reported.
period. This provides an indication of the balance ability to
5.4.2 Calibration shall be carried out under stable environ-
produce consistent results, expressed as a standard deviation.
mental conditions, where possible. Calibration shall be carried Repeatability conditions include:
out within the normal working environmental conditions of the
(1) The same measurement procedure;
installation site.
(2) The same operator;
5.4.3 The test loads should be acclimatized to the environ- (3) The same measurement system; and
mental conditions in the vicinity of the balance before calibra- (4) The same operating conditions and the same location.
E898 − 20
6.2.5 The test load should consist of a single weight location of measurement points can vary depending on the
whenever possible. shape of the pan.
6.2.6 For balances with only a single scale interval, the test
6.2.10 Depending on the mechanical construction of the
load is usually chosen between approximately 50 % of the
balance, the eccentricity test might not be possible or required,
maximum capacity and approximately 100 % of the maximum
for example, for balances with a hanging weighing pan or
capacity. If the customer requires a special measurement point,
hopperscales.Caremustbetakenwhenperformingthisteston
the test load value can be adjusted. A typical application for
balances with leveling pans to position weights so that they do
which the repeatability test load may be adjusted is weighing
not tip off the tilted pan surface.
quantitiesonthebalancewithmassvaluessignificantlysmaller
6.2.11 The measurement can be performed with the follow-
than maximum capacity.
ing methods:
6.2.7 For multi-interval/multiple range balances, the test
6.2.11.1 Method 1 (Recommended for Single Range
loads are usually chosen between approximately 50 % to
Balances)—Set the value to zero before measuring. Place the
approximately 100 % of the upper limit of each interval/range.
test load at position 1 and then move to the other positions in
If the customer requires a special measurement point, the test
sequence. The indication is recorded for each position.
load value can be adjusted.Atypical application for which the
6.2.11.2 Method 2 (Recommended for Multi-interval/
repeatability test load may be adjusted is weighing quantities
Multiple Range Balances)—First place the test load in position
on the balance with mass values significantly smaller than
1 and perform a tare operation on the balance. The test load is
maximum capacity.
then moved sequentially to the other positions. The indication
6.2.8 Beforeeachmeasurement,setthebalancetozero,load
is recorded for each position.
the test load in the middle of the balance weighing pan, and
6.2.11.3 Method 3 (Recommended for Single Range Bal-
record the indication after stabilization. For all balances with a
ances that Might Easily Show Drift)—Set the value to zero
scale interval of 0.1 mg and finer, complete a minimum of 10
beforemeasuring.Firstplacethetestloadinposition1,remove
measurements.Forallbalanceswithascaleintervallargerthan
it, then place it in the next position, remove it, and so on, until
0.1 mg, complete a minimum of 5 measurements. For multi-
it is removed from the last position. For each position, record
interval/multiple range balances, the number of measurements
the indication. The indication is set to zero each time the load
shall be the same in all intervals/ranges. The smallest scale
is removed.
interval shall be taken as reference for defining the minimum
6.2.11.4 Method 4 (Recommended for Multi-interval/
number of measurements.
Multiple Range Balances that Might Easily Show Drift)—First
6.2.9 Measurement of Eccentric Loading—The error of
place the test load in position 1 and perform a tare operation on
indication of the same load at different positions on the
the balance. Move the test load to the first off-center position
weighingpanisexpressedbythemaximumdifferencebetween
and then move back to position 1. Record the indication for the
theindicationofthedifferentpositionsandtheindicationofthe
off-center position. When the load is back at position 1 and if
center position.Asingle weight should be used when possible.
the display is not zero, then the indication is set to zero before
For multi-interval/multiple range as well as single range
continuing. Move the test load to the next off-center position,
balances, the test load is preferably approximately one-third of
and back to position 1. Continue until the test load has been
the maximum capacity. Measurements include placing the test
removed from the last off-center and center positions.
load at different locations on the pan in such a way as to ensure
that the center of gravity of the applied load is at the positions
NOTE 2—If the weighing system auto-zero is activated, the eccentric
shown in Fig. 1, or as close as possible. The number and loading test results can be affected, resulting in a falsely small error. The
FIG. 1 Load Positions
E898 − 20
calibration technician must be observant of such effects and disable the
In the formula:
auto-zero, if necessary, to obtain correct results (see 6.2.3).
th
I =i position indication (i = 2, 3, …), and
Li
6.2.12 Measurement of Error of Indication—The measuring I = center position indication.
L1
points should be uniformly selected within the weighing range
7.3.2 The maximum error of eccentric loading is the value
to be calibrated, as far as reasonably possible. At least 5
reported and included in uncertainty calculations.
different test loads shall be required, including zero and
maximum capacity or close to the maximum capacity (for
8. Evaluation of Measurement Uncertainty
example, 0, 25, 50, 75, and 100 % of maximum capacity).
While the following sections document the likely uncer-
Measurement points may be added according to customer
tainty for the balance calibration, error sources contributing to
needs. Ideally, each test load should consist of a single weight;
uncertainty may be added or removed as appropriate for the
however, multiple weights may be used when necessary to
situation. The error sources described in this practice are the
achieve the appropriate test load. Before each measurement,
most likely to consider.
the indication value is set to zero. The measurement can be
8.1 Standard Uncertainty of the Error of Indication During
selected according to the following methods:
Calibration—The measurement model of the error of indica-
6.2.12.1 Method 1—Increase from zero load to maximum
tion is:
capacity. Unload the weights at each step of the measurement
E 5 I 2 m (7)
process.After unloading, check the zero point. If the zero point
ref
is not zero, set the value to zero.
The formula for calculating the combined standard uncer-
6.2.12.2 Method 2—Increase from zero load to maximum
tainty is:
capacity; no need to unload the weights during the measure-
2 2 2
u E 5 u I 1u m (8)
~ ! ~ ! ~ !
c ref
ment. This method may produce creep effects in the results.
8.1.1 Standard Uncertainty of the Indication u(I)—The
6.2.12.3 Method 3—If the customer requests, the measure-
measurement model for the indication is:
ment can also be performed from maximum capacity to zero
load, without unloading weights after each measurement.As in
I 5 I 1δI 1δI 1δI 2 I 2δI (9)
L digL rep ecc 0 dig0
Method 2, this may produce creep effects in the results.
8.1.1.1 Standarduncertaintycausedbytheroundingerrorof
the no-load indication u(δI ). δI represents the rounding
dig0 dig0
7. Calibration Results
error of the no-load indication. The half width of the scale
7.1 Error of Indication Measurement Results—For each test
interval is d /2, a rectangular distribution is assumed:
load, the error of indication (E) is calculated as follows:
d
u~δI ! 5 (10)
E 5 I 2 m (1) dig0
ref
~2 =3!
7.1.1 For the value of the reference mass, the nominal mass
8.1.1.2 Standarduncertaintycausedbytheroundingerrorof
of the test load can be taken:
the indication at load u(δI ). δI represents the rounding
digL digL
m 5 m (2)
error of the indication at load. The half width of the scale
ref N
interval is d /2, a rectangular distribution is assumed:
L
7.1.2 Alternatively, the conventional mass va
...

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: E898 − 88 (Reapproved 2013) E898 − 20
Standard Test Method of Testing Practice for
Top-Loading, Direct-Reading Laboratory Scales and
BalancesCalibration of Non-Automatic Weighing
Instruments
This standard is issued under the fixed designation E898; 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.
INTRODUCTION
This method is designed to test commonly used laboratory scales that read the entire range of weight
up to the capacity without manual operation. In essence, the entire reading range is on-scale and no
manipulation of weights, riders, or dials is required; except some scales with optical reading devices
may require the operation of a micrometer dial to interpolate the final one or two significant figures.
1. Scope
1.1 This test method covers the determination of characteristics of top-loading, direct-reading laboratory scales and balances.
Laboratory scales of the top-loading type may have capacities from a few grams up to several kilograms. Resolution may be from
1/1000 of capacity to 1/1 000 000 or more. This method can be used for any of these instruments and will serve to measure the
most important characteristics that are of interest to the user. The characteristics to be measured include the following:
1.1.1 warm-up,
1.1.2 off center errors,
1.1.3 repeatability, reproducibility, and precision,
1.1.4 accuracy and linearity,
1.1.5 hysteresis,
1.1.6 settling time,
1.1.7 temperature effects,
1.1.8 vernier or micrometer calibration, and
1.1.9 resistance to external disturbances.
1.2 The types of scales that can be tested by this method are of stabilized pan design wherein the sample pan does not tilt out
of a horizontal plane when the sample is placed anywhere on the pan surface. The pan is located generally above the measuring
mechanism with no vertical obstruction, except for draft shields. Readings of weight may be obtained from an optical scale, from
a digital display, or from a mechanical dial. Weighing mechanisms may be of the deflecting type, using gravity or a spring as the
transducer, or may be a force-balance system wherein an electromagnetic, pneumatic, hydraulic, or other force is used to
counterbalance the weight of the sample. Other force-measuring devices may be tested by this method as long as a sample placed
on a receiving platform produces an indication that is substantially a linear function of the weight of the sample.
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 health practices and determine the applicability of regulatory
limitations prior to use.
2. Summary of Method
2.1 Throughout this method, the instrument is used in the manner for which it is intended. One or more weights are used to test
each of the characteristics, and the results are expressed in terms of the least count or ultimate readability of the display.
This test method practice is under the jurisdiction of ASTM Committee E41 on Laboratory Apparatus and is the direct responsibility of Subcommittee E41.06 on
Weighing DevicesLaboratory Instruments and Equipment.
Current edition approved Dec. 1, 2013May 1, 2020. Published December 2013 June 2020. Originally approved in 1982. Last previous edition approved in 20052013 as
E898 – 88(2005).(2013). DOI: 10.1520/E0898-88R13.10.1520/E0898-20.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E898 − 20
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
3.1.1 accuracy—the degree of agreement of the measurement with the true value of the quantity measured.
3.1.2 capacity—the maximum weight load specified by the manufacturer. In most instruments, the maximum possible reading
will exceed the capacity by a small amount.
3.1.3 full-scale calibration—the indicated reading when a standard weight equal to the full scale indication of the scale is placed
on the sample pan after the device has been correctly zeroed. Usually some means is provided by the manufacturer to adjust the
full scale indication to match the weight of the standard.
3.1.4 linearity—the degree to which a graph of weight values indicated by a scale vs. the true values of the respective test
weights approximates a straight line. For a quantitative statement of linearity errors, the concept of terminal-based non-linearity
is recommended, such as, the maximum deviation of the calibration curve (average of the readings at increasing and decreasing
test load, respectively) from a straight line drawn through the upper and lower endpoints of the calibration curve.
3.1.5 off-center errors—differences in indicated weight when a sample weight is shifted to various positions on the weighing
area of the sample pan.
3.1.6 hysteresis—difference in weight values indicated at a given test load depending on whether the test load was arrived at
by an increase or a decrease from the previous load on the scale.
3.1.7 repeatability—closeness of agreement of the indicated values for successive weighings of the same load, under essentially
the same conditions, approaching from the same direction (such as, disregarding hysteresis).
3.1.8 reproducibility—closeness of agreement of the indicated values when weighings of the same load are made over a period
of time under essentially the same conditions but not limited to the same direction of approach (such as, hysteresis errors are
included).
3.1.9 precision—the smallest amount of weight difference between closely similar loads that a balance is capable of detecting.
The limiting factor is either the size of the digital step of the indicator readout or the repeatability of the indicated values.
3.1.10 standard deviation—used as a quantitative figure of merit when making statements on the repeatability, reproducibility
or precision of a balance.
3.1.11 readability—the value of the smallest unit of weight that can be read without estimation. In the case of digital
instruments, the readability is the smallest increment of the least significant digit (for example, 1, 2 or 5). Optical scales may have
a vernier or micrometer for subdividing the smallest scale division. In that case, the smallest graduation of the vernier or
micrometer represents the readability.
3.1.12 standard weight—any weight whose mass is given. Since weights are not always available with documented corrections,
weights defined by class may be used if the class chosen has sufficiently small limits and there is an understanding that errors
perceived as being instrumental in nature could be attributed to incorrectly adjusted weights.
4. Significance and Use
4.1 This method will enable the user to develop information concerning the precision and accuracy of weighing instruments.
In addition, results obtained using this method will permit the most advantageous use of the instrument. Weaknesses as well as
strengths of the instrument should become apparent. It is not the intent of this method to compare similar instruments of different
manufacture, but to enable the user to choose a suitable instrument.
5. Apparatus
5.1 Manufacturer’s Manual.
5.2 Standard Weights—A set of weights up to the capacity of the scale with sufficient subdivisions of weight so that increments
of about 10 % of the capacity up to the capacity can be tested.
5.3 Thermometer, room temperature, with a resolution of at least 1 °C.
5.4 Stop-Watch, reading to ⁄5 s.
6. Preparation
6.1 Make sure that the scale and weights are clean.
6.2 Place the standard weights near the instrument.
6.3 Place the thermometer on the bench in such a position that it can be read without being touched.
6.4 Allow the instrument and the weights to sit undisturbed for at least 2 h with the balance turned off. Monitor the temperature
during this time to make sure that there is no more than approximately 2°C variation over the last hour before beginning the test.
E898 − 20
6.5 Read the manufacturer’s instructions carefully. During each step of the test procedure, the instrument should be used in the
manner recommended by the manufacturer. Know the location of any switches, dials, or buttons as well as their functions.
7. Test Procedure
7.1 Warm-up Test:
7.1.1 If it is required in the normal operation of the scale to turn it “on” as an operation separate from weighing, perform that
operation simultaneously with the starting of the stop-watch.
7.1.2 If a zeroing operation is required, do it promptly. Record the temperature.
7.1.3 At the end of 1 min, read and record the indication with the pan empty.
7.1.4 At the center of the sample pan place a standard weight nearly equal to but not exceeding 98 % of the capacity of the scale.
If the scale allows no weight readings above the stated nominal capacity, then this test should be performed with standard weights
equal to 90 % of capacity. When the indication is steady, record the indication and remove the weight from the pan.
7.1.5 At the end of 5 min, repeat steps 7.1.3 and 7.1.4 without rezeroing.
7.1.6 At the end of 30 min, repeat again.
7.1.7 At the end of 1 h, repeat again. Record the temperature.
7.1.8 Compute for each measurement as follows:
k 5 W/ I 2 I (1)
~ !
t w o
where:
I = indication with the standard weight on the pan,
w
I = indication with pan empty,
o
W = known or assumed value of the standard weight, and
k = calibration factor for time t.
t
7.1.9 Plot the values of k against the time (1 min, 5 min, 30 min, and 60 min). The time at which k apparently no longer drifts
t t
in one direction can be assumed to be the warm-up time required.
7.1.10 If there is a user-adjustable full-scale calibration procedure recommended by the manufacturer, this adjustment should
be made after the warm-up time determined in 7.1.9.
7.1.11 If the calibration cannot be adjusted by the user, the factor k can be used as a multiplier for an indicated weight to correct
t
to true weight.
7.1.12 Plot I as a function of time to determine the zero drift. For individual measurements of weight, the zero can be
o
monitored or corrected prior to a weighing. However, if the change in weight of a sample as a function of time is of importance,
and if the sample cannot be removed for zeroing, it is also important to know the course of the zero as a function of time.
7.2 Off-Center Errors—The geometry of the stabilizing mechanism for the sample pan determines whether or not the scale is
sensitive to the position of the load on the pan. This effect is measured by placing the load in various positions on the pan and
observing any difference in indication. Place the standard weight (100 % or 90 % of capacity, as per 7.1.4) in 5 positions on the
pan, noting the indication for each position: center-front-back—right-left; or center and corners. The difference between the lowest
and the highest indication is the maximum off-center error.
7.3 Repeatability—A computation of the standard deviation (σ) of a series of observations at the same load apapproached from
the same direction provides a measure of precision. The computation of 3σ will indicate with a high degree of assurance that any
single measurement will fall within that limit of error, providing hysteresis is negligible. A control chart can be generated by
periodically remeasuring the standard deviation and plotting it as a function of time (perhaps by date). Any time that the standard
deviation falls outside of a pattern of values (control limits) there may be a reason to investigate the instrument or the measuring
technique to determine whether adjustments may be required.
7.4 Hystersis—Balances do not usually have problems with hysteresis. Nevertheless the test for hysteresis is simple and should
be performed on newly-acquired balances. Perform the test as follows:
7.4.1 Zero the balance,
7.4.2 Place a weight or weights equal to about one-half the balance capacity on the pan and record the reading once it is stable,
7.4.3 Add more weights to the balance pan until 90 % to 100 % of full capacity is reached. Wait for a stable reading, although
the actual value need not be recorded.
7.4.4 Remove the weights which were added in 7.4.3 and record the balance reading once it is stable.
7.4.5 Remove the rest of the weights from the balance and record the reading as soon as it is stable. The five operations can
be shown in tabular form:
Operation Weight on Pan Balance Reading
1 nil 0
2 ⁄2 capacity W1
3 full capacity W2
4 ⁄2 capacity W1'
5 nil Z
E898 − 20
If the quantity W1 − W1' + Z ⁄2 differs significantly from zero, the difference can be attributed to hysteresis. The test may be
repeated several times and the results averaged to reduce measurement scatter.
7.5 Precision—To calculate the balance precision, combine the uncertainties due to lack of repeatability and to hysteresis.
7.6 Accuracy and Linearity—These tests are made together because they represent the same thing. Since accuracy represents
the proximity to true value, the nonlinearity is a point-by-point measure of accuracy if the zero point and the full-scale calibration
point have been set true. Set the zero and full-scale indications as described in 7.1.10 if possible. Place weights on the pan in
increasing increments of about 10 % of the capacity and observe the indications. Plot the indicated values against the known or
assumed value of the weight. The difference at any point is the inaccuracy. Keep in mind that the accuracy cannot be better than
the precision and that every observation includes an uncertainty of as much as 3σ so that specifying a higher accuracy may be
misleading. However, a procedure that includes multiple observations at each point and which minimizes any hysteresis effects and
off-center errors can improve the precision, and therefore produce an accuracy measurement which is more significant.
7.7 Settling Time—The time for an indication to reach a stable value after the application of a load is a measure of how soon
an indication may be read. This time is controlled by several factors including the moment of inertia of the system, the degree of
damping or, in the case of digital instruments, the time-constant of the digital conversion rate. In addition, some digital designs
may permit a flicker between two or more digits because of hunting in a servo loop. A knowledge of the time required may prevent
a reading in error. Zero the scale in accordance with the manufacturer’s instructions. Place a standard weight equal to the capacity
of the scale on the pan simultaneously starting the stop-watch. Stop the watch when it appears that the indication is steady. Record
the elapsed time. Repeat several times to ensure that there is reasonable correlation between measurements.
7.8 Temperature Effects—The ambient temperature may have an effect on the zero as well as the full-scale calibration. If means
are available to test the instrument at various temperatures, such a test can be valuable, especially if the location in which the
instrument is used is subject to variable temperature. Precaution should be taken to avoid moving the instrument from one location
to another in order to take advantage of different existing temperatures. Moving the instrument may introduce other effects which
could mask the variability with temperature.
7.9 Vernier or Micrometer Calibration—Some optical scales are equipped with a device for subdividing the smallest increment
of the main scale. In order to subdivide correctly, the full range of the subdividing device must exactly equal one scale graduation.
In the case of a vernier, this can be accomplished by carefully zeroing the instrument and observing the coincidence of the first
and last line of the vernier with the corresponding lines on the main scale. Usually, if the first (zero) line of the vernier is coincident
with the zero line of the main scale, the last line of the vernier should be coincident with the line of the main scale which is one
less than the number of graduations on the vernier (for example, 10 graduations on the vernier corresponding with 9 graduations
on the main scale). In the case of a micrometer which may subdivide a scale division into 100 parts, this test is not as simple
because the micrometer usually is limited to 99 subdivisions in order to avoid ambiguities in reading. Therefore, the range of the
micrometer cannot be examined by turning it through its entire range. One test which can be performed is to set the micrometer
to read 00. Zero the instrument to some scale line higher than zero. Operate the micrometer to read 99. It should not be possible
to bring the next lower line of the main scale into coincidence with the cursor. If possible, check the micrometer more precisely
by using a test weight equal to 99 readable units. Combinations of small weights can be used to make up this value. Zero the
instrument. Place the weights on the pan and operate the micrometer to bring the cursor into coincidence. Observe the displayed
weight and compare with the true value of the weights on the pan. If the displayed weight is in error by more than one readable
unit, adjust the display if such an adjustment is recommended by the manufacturer.
7.10 Resistance to External Effects—Some digital devices can show disturbances in the display due to RFI (radio frequency
interference). Quantitative testing is difficult but operating a citizens band radio transmitter near the instrument can give some
information about the susceptibility to RFI. Electromagnetic force-balance instruments may have insufficient shielding and may,
therefore, react to the influence of strong magnetic fields nearby. Passing a small permanent magnet around the instrument and
observing changes in display will give information about this effect. Moving the instrument from a metal topped bench to one
which is nonmagnetic and observing a difference in full-scale calibration will give some qualitative information about any
sensitivity in this area.
8. Interpretation of Results
8.1 Each of the tests listed are designed to give pertinent information about the instrument. The importance of any one test will
depend on the needs of the user. If the tests are to be used for qualifying an instrument for a procedure, those tests which are
pertinent to that procedure should, obviously, be performed.
9. Precision and Bias
9.1 For statements on precision and bias, refer to 7.5 and 7.6.
E898 − 20
10. Keywords
10.1 balances; direct reading; laboratory; scales; top-loading
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1. Scope
1.1 This practice applies to the calibration of electronic non-automatic weighing instruments. A non-automatic weighing
instrument is a measuring instrument that determines the mass of an object by measuring the gravitational force acting on the
object. It requires the intervention of an operator during the weighing process to decide whether the weighing result is acceptable.
1.2 Non-automatic weighing instruments have capacities from a few grams up to several thousand kilograms, with a scale
interval typically from 0.1 micrograms up to 1 kilogram. Note that non-automatic weighing instruments are usually referred to as
either balances or scales. In this practice, for brevity, non-automatic weighing instruments will be referred to as balances; however,
the scope of this practice also includes scales.
1.3 This practice only covers electronic non-automatic weighing instruments where the indication is obtained from a digital
display. The measuring principle is usually based on the force compensation principle. This principle is realized either by elastic
deformation, where the gravitational force of the object being weighed is measured by a strain gauge that converts the deformation
into electrical resistance, or by electromagnetic force compensation, where the gravitational force is compensated for by an
electromagnetic counterforce that holds the load cell in equilibrium.
1.4 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this
standard.
1.5 This standard does not purport to be suitable as the sole testing process for weighing systems designated for commercial
service under weights and measures regulation. The legal requirements for such instruments vary from region to region, and also
depend on specific applications. To determine applicable legal requirements, contact the weights and measures authority in the
region where the device is located.
1.6 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.
1.7 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:
E617 Specification for Laboratory Weights and Precision Mass Standards
2.2 ISO Standards:
ISO 9001 Quality Management Systems – Requirements
ISO/IEC 17025 General Requirements for the Competence of Testing and Calibration Laboratories
2.3 OIML Documents and Recommendations:
D28 Conventional Value of the Result of Weighing in Air
R76-1 Non-automatic Weighing Instruments – Part 1: Metrological and Technical Requirements – Tests
ANSI/ISA S51.1 “Process Instrumentation Technology”. Available from American National 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 Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036.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.
Available from the Organisation Internationale de Métrologie Légale (OIML), 11 Rue Turgot, 75009 Paris, France, https://www.oiml.org/en.
E898 − 20
R111-1 Weights of classes E , E , F , F , M , M , M and M – Part 1: Metrological and Technical Requirements
1 2 1 2 1-2 2 2-3 3
2.4 EURAMET Guide:
Calibration Guide No. 18 Guidelines on the Calibration of Non-automatic Weighing Instruments
2.5 JCGM Guides:
JCGM 100 Evaluation of Measurement Data – Guide to the Expression of Uncertainty in Measurement (GUM)
JCGM 200 International Vocabulary of Metrology – Basic and General Concepts and Associated Terms (VIM)
2.6 ILAC Guideline:
ILAC-G24 Guidelines for the Determination of Calibration Intervals of Measuring Instruments, ILAC-G24
2.7 USP General Chapters:
USP General Chapter 41 Balances
USP General Chapter 1251 Weighing on an Analytical Balance
2.8 UKAS Guide:
UKAS LAB 14, Edition 5 In-house Calibration and Use of Weighing Machines
2.9 Code of Federal Regulations:
CFR Part 58 Good Laboratory Practice for Nonclinical Laboratory Studies
CFR Part 211 Current Good Manufacturing Practice for Finished Pharmaceuticals
2.10 FDA Guidance:
FDA Questions and Answers on Current Good Manufacturing Practices, Good Guidance Practices, Level 2 Guidance –
Equipment
For dated references, only the dated version applies to this practice. For undated references, the latest edition (including all
amendments) applies to this practice.
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
3.1.1 In this section, the official definitions of the terms are provided, as are, where appropriate, simplified definitions that relate
the terms to the scope of this practice.
3.1.2 accuracy class of weights, n—class designation of a weight or weight set which meets certain metrological requirements
intended to maintain the mass values within specified limits.
3.1.3 calibration, n—operation that establishes a relation between the indication of the weighing instrument and the reference
weights, including the associated measurement uncertainties.
3.1.3.1 Discussion—
An operation that, under specified conditions, in a first step, establishes a relation between the quantity values with measurement
uncertainties provided by measurement standards and corresponding indications with associated measurement uncertainties and,
in a second step, uses this information to establish a relation for obtaining a measurement result from an indication.
3.1.4 conventional mass value, n—mass value indicated in the calibration certificate of the weight.
3.1.4.1 Discussion—
The conventional mass value of a body is equal to the mass of a standard that balances this body under conventionally chosen
3 3 14
conditions, that is, at 20 °C, a density of the standard of 8000 kg ⁄m in air of density 1.2 kg ⁄m .
3.1.5 coverage factor (k), n—number larger than one by which a combined standard measurement uncertainty is multiplied to
obtain an expanded measurement uncertainty.
3.1.5.1 Discussion—
Available from EURAMET e.V., Bundesallee 100, 38116 Braunschweig, Germany, https://www.euramet.org.
Available from the Bureau International des Poids et Mesures, Pavillon de Breteuil, 92312 Sèvres, France, https://www.bipm.org.
Available from the International Laboratory Accreditation Cooperation, ILAC Secretariat, PO Box 7507, Silverwater NSW 2128, Australia, https://ilac.org.
Available from U.S. Pharmacopeial Convention (USP), 12601 Twinbrook Pkwy., Rockville, MD 20852-1790, http://www.usp.org.
Available from the United Kingdom Accreditation Service (UKAS), 2 Pine Trees, Chertsey Lane, Staines-upon-Thames, TW18 3HR, UK, https://www.ukas.com.
Available from the United States Federal Register, https://www.archives.gov/federal-register.
Available from U.S. Food and Drug Administration (FDA), 10903 New Hampshire Ave., Silver Spring, MD 20993, http://www.fda.gov.
Definition from OIML R111-1.
Definition from JCGM 200 (VIM).
Definition from OIML D28.
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The coverage factor (k) is typically calculated based on the applicable degrees of freedom (ν).
3.1.6 eccentric loading error, n—error when the load is not placed in the center of the weighing platform.
3.1.6.1 Discussion—
The deviation in the measurement value caused by asymmetrical placement of the center of gravity of the load relative to the load
receptor.
3.1.7 error, n—difference between the indicated quantity and the applied quantity.
3.1.7.1 Discussion—
Error is the measured quantity value minus a reference quantity value.
3.1.8 linearity, n—ability of a weighing instrument to follow the linear relationship between a load and the indication.
3.1.9 maximum capacity, n—maximum weighing capacity, that is, the maximum capacity whose weight can be determined on
a balance.
3.1.10 maximum permissible error (mpe), n—limit by which the measured quantity indication can deviate from the nominal
applied value.
3.1.10.1 Discussion—
The extreme value of measurement error, with respect to a known reference quantity value, permitted by specifications or
regulations for a given measurement, measuring instrument, or measuring system.
3.1.11 measurement standard, n—realization of the definition of a given quantity, with stated quantity value and associated
measurement uncertainty, used as a reference.
3.1.12 measurement uncertainty, n—parameter that quantifies how far a measurement value might be away from the true
(unknown) value.
3.1.12.1 Discussion—
The non-negative parameter characterizing the dispersion of the quantity values being attributed to a measurand, based on the
information used.
3.1.13 minimum weight, n—smallest sample weight required for a weighment to just achieve a specified relative accuracy of
weighing.
3.1.14 nominal capacity, n—nominal value of the weighing capacity, derived from the maximum capacity by rounding it down
to a number with less significant digits.
3.1.15 repeatability, n—ability of a weighing instrument to provide indications that are close together when weighing the same
object several times under reasonably constant test conditions.
3.1.15.1 Discussion—
The ability of an instrument to provide results that agree one with the other when the same load is deposited several times and
in a practically identical way on the load receptor under reasonably constant test conditions.
3.1.16 scale interval, n—the difference between two consecutive indicated values.
3.1.17 sensitivity, n—change in indication divided by change in the applied quantity.
3.1.17.1 Discussion—
The quotient of the change in an indication of a measuring system and the corresponding change in a value of a quantity being
measured.
Nater, R., Reichmuth, A., Schwartz, R., Borys, M., and Panagiotis, Z., Dictionary of Weighing Terms, Springer, ISBN 978-3-642-02013-1, 2009.
Definition from OIML R76-1.
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3.2 Symbols:
d—scale interval
D—drift, value change with time
d —smallest scale interval
E—error of indication
I —indication
k—coverage factor
L—load
m —object mass
Max—maximum capacity
Max —upper limit of partial weighing range with smallest scale interval
m —conventional value of mass
c
m —minimum weight
min
m —nominal mass
N
mpe—maximum permissible error of a measured quantity
m —reference mass
ref
n—number of repeated weighings
R—reading
s—standard deviation
SF—safety factor
T—temperature (unit K)
u—standard uncertainty
U—expanded uncertainty
u —combined standard uncertainty
c
α—intercept (for uncertainty in use)
β—slope (for uncertainty in use)
ν—degrees of freedom
ν —effective degrees of freedom for combined standard uncertainty
eff
ρ—density
ρ —reference density of air, ρ = 1.2 kg/m
0 0
ρ —reference density of mass, ρ = 8000 kg/m
c c
ρ —density of standard weights
S
3.3 Symbol Subscripts and Definitions
Subscript Related
B air buoyancy
conv convection
D drift
L load
N nominal value
dig digitization
ecc load in different locations on the weighing pan
i, j number
max maximum
min minimum
ref reference
rep repeatability
0 no load
4. Significance and Use
4.1 This practice will enable calibration laboratories and the user to calibrate electronic non-automatic weighing instruments
and quantify the error of the balance throughout the measurement range, usually from zero to maximum capacity. The error of
indication is accompanied by a statement on measurement uncertainty, which is individually estimated for every measurement
point. This practice is based on the test procedures and uncertainty estimation described in the EURAMET calibration guide cg-18.
However, while EURAMET cg-18 allows for a very flexible execution of the measurements, the test procedures described in this
practice are more fixed to enable a better comparability between calibrations executed by different calibration laboratories or users.
This practice may also serve as basis for accreditation of calibration laboratories for calibration of electronic non-automatic
weighing instruments.
4.2 This practice allows the user to decide whether the calibrated balance is fit for its intended purpose, based on the assessment
of the calibration results. Usually, this assessment is done by ensuring that the measurement uncertainty of all weighings the user
performs on the instrument is smaller than a specified relative tolerance established by the user. This approach is commensurate
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to assuring that the smallest net amount of substance that the user weighs on the instrument (so-called smallest net weight) is larger
than the minimum weight, which is derived from the calibration results.
4.3 This practice, in Appendix X2, provides information on the periodic performance verification on the balance that should be
carried out by the user between the calibrations. Calibration together with periodic performance verification allows the user to
ensure with a very high degree of probability that the balance meets the user requirements during its day-to-day usage. It helps
users comply with requirements from other standards or regulations that stipulate periodic tests and calibrations of quality-relevant
instruments.
5. Calibration Conditions
5.1 Standard Weights
5.1.1 General Requirements—Test loads shall consist of standard weights that are traceable to the SI unit of mass, with the
possible exception of test loads used for measurements of a comparative nature—for example, measurement of eccentric loading
or repeatability.
5.1.2 Standard Weight Traceability—The traceability of weights to be used as standards shall be demonstrated by calibration
consisting of:
5.1.2.1 Determination of the conventional value of mass m or the correction δm to its nominal value m :δm 5m 2m , or both,
c c N c c N
together with the expanded uncertainty of the calibration U, or
5.1.2.2 Confirmation that m is within specified maximum permissible errors mpe: m 2~mpe2U!#m #m 1~mpe2U!.
c N c N
5.1.2.3 The standards should further satisfy the following requirements to an extent appropriate to their accuracy:
kg
(1) Density ρ sufficiently close to ρ 58000 ,
c 3
s
m
(2) Surface finish suitable to prevent a change in mass through contamination by dirt or adhesion layers, and
(3) Magnetic properties such that interaction with the instrument to be calibrated is minimized.
5.1.2.4 Weights that comply with the relevant specifications of OIML R111-1 or Specification E617 should satisfy all these
requirements.
5.1.3 Recommendation for the Selection of Weight Classes—It is recommended selecting the weights in order to minimize their
uncertainty contribution to the balance uncertainty as far as reasonably possible so that user tolerance requirements are met. The
following selection criteria for weight classes could be considered:
5.1.3.1 1 000 000 < Max/d: Select an OIML E or ASTM Class 1 weight, or a weight with uncertainty not worse than the
permitted OIML E or ASTM Class 1 uncertainty, which is one-third or less of the maximum permissible error; it is recommended
to always use the conventional mass value as the reference value;
5.1.3.2 150 000 < Max/d ≤ 1 000 000: For a weight where the nominal value is used as the reference value, select an OIML
F or ASTM Class 2 weight or better; for a weight where the conventional mass value is used as the reference value, select an
OIML F or ASTM Class 4 weight or better;
5.1.3.3 15 000 < Max/d ≤ 150 000: For a weight where the nominal value is used as the reference value, select an OIML F
or ASTM Class 4 weight or better; for a weight where the conventional mass value is used as the reference value, select an OIML
M or ASTM Class 5 weight or better; and
5.1.3.4 Max/d ≤ 15 000: For a weight where the nominal value is used as the reference value, select an OIML M or ASTM
Class 5 weight or better; for a weight where the conventional mass value is used as the reference value, select an OIML M or
ASTM Class 6 weight or better.
5.1.3.5 For multi-interval and multiple range balances, Max and d refer to the interval/range with the smallest scale interval,
abbreviated as Max and d , respectively.
1 1
5.2 Substitution Loads
5.2.1 Calibration requiring substitution loads is not within the scope of this practice. Substitution is discussed elsewhere (see
EURAMET cg-18).
5.3 Other Measuring Instruments Used for Calibration
5.3.1 Thermometer for monitoring air temperature with a resolution of 0.5 °C or better.
5.3.2 Hygrometer for monitoring ambient relative humidity with a resolution of 5 % RH or better.
5.4 Calibration Environmental Conditions
5.4.1 Environmental temperature and relative humidity shall be recorded and reported.
5.4.2 Calibration shall be carried out under stable environmental conditions, where possible. Calibration shall be carried out
within the normal working environmental conditions of the installation site.
5.4.3 The test loads should be acclimatized to the environmental conditions in the vicinity of the balance before calibration.
Non-acclimatized weights trigger a convection effect of the surrounding air that may impact the indication of the balance.
Information on acclimatization times may be found, for example, in EURAMET cg-18, Specification E617, or OIML R111-1.
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6. Calibration Practice
6.1 Measurement Parameters General—This practice includes the following measurement parameters:
Repeatability;
Eccentric loading; and
Error of indication.
6.1.1 These three measurements may be performed in any order to accommodate efficient usage of weights and detect potential
defects of the weighing instrument at an early stage.
6.2 Calibration
6.2.1 Calibration Range—The calibration range is typically from the zero point of the balance to maximum capacity, or the
weighing range specified by the customer.
6.2.2 Calibration Location—Calibration shall be performed at the location of use of the balance. If calibration at the location
of use is not possible, then this exception shall be noted in the calibration certificate. If the balance is moved to another location
after calibration, the following situations may occur:
(1) Difference in local gravitational acceleration;
(2) Changes in environmental conditions; and
(3) Impact (damage) during transport.
NOTE 1—Each of the above may cause the performance of the balance to change and can invalidate the calibration. Therefore, moving the balance after
calibration should be avoided. Recalibration of the balance is recommended after it has been moved if evidence of altered performance cannot be
excluded.
6.2.3 Preparation Before Calibration—Check the balance nameplate or product identification. Identify the model, scale interval,
maximum capacity, serial number, manufacturer, and other applicable information. The balance shall be energized at an appropriate
time prior to calibration, such as the warm-up time specified in the balance instructions or the time set by the user.
6.2.3.1 If there is no such rule, the balance warm-up time should be no less than 30 min.
6.2.3.2 If as-found data is to be collected, do not level prior to as-found calibration. The balance should be levelled before as-left
calibration.
6.2.3.3 If the balance is equipped with an auto-zero function, this function should be turned off before calibration, if possible.
6.2.4 Measurement of Repeatability—Under repeatability conditions, the same load is placed on the balance pan several times
in a practical and consistent manner in a short time period. This provides an indication of the balance ability to produce consistent
results, expressed as a standard deviation. Repeatability conditions include:
(1) The same measurement procedure;
(2) The same operator;
(3) The same measurement system; and
(4) The same operating conditions and the same location.
6.2.5 The test load should consist of a single weight whenever possible.
6.2.6 For balances with only a single scale interval, the test load is usually chosen between approximately 50 % of the maximum
capacity and approximately 100 % of the maximum capacity. If the customer requires a special measurement point, the test load
value can be adjusted. A typical application for which the repeatability test load may be adjusted is weighing quantities on the
balance with mass values significantly smaller than maximum capacity.
6.2.7 For multi-interval/multiple range balances, the test loads are usually chosen between approximately 50 % to approxi-
mately 100 % of the upper limit of each interval/range. If the customer requires a special measurement point, the test load value
can be adjusted. A typical application for which the repeatability test load may be adjusted is weighing quantities on the balance
with mass values significantly smaller than maximum capacity.
6.2.8 Before each measurement, set the balance to zero, load the test load in the middle of the balance weighing pan, and record
the indication after stabilization. For all balances with a scale interval of 0.1 mg and finer, complete a minimum of 10
measurements. For all balances with a scale interval larger than 0.1 mg, complete a minimum of 5 measurements. For
multi-interval/multiple range balances, the number of measurements shall be the same in all intervals/ranges. The smallest scale
interval shall be taken as reference for defining the minimum number of measurements.
6.2.9 Measurement of Eccentric Loading—The error of indication of the same load at different positions on the weighing pan
is expressed by the maximum difference between the indication of the different positions and the indication of the center position.
A single weight should be used when possible. For multi-interval/multiple range as well as single range balances, the test load is
preferably approximately one-third of the maximum capacity. Measurements include placing the test load at different locations on
the pan in such a way as to ensure that the center of gravity of the applied load is at the positions shown in Fig. 1, or as close as
possible. The number and location of measurement points can vary depending on the shape of the pan.
6.2.10 Depending on the mechanical construction of the balance, the eccentricity test might not be possible or required, for
example, for balances with a hanging weighing pan or hopper scales. Care must be taken when performing this test on balances
with leveling pans to position weights so that they do not tip off the tilted pan surface.
6.2.11 The measurement can be performed with the following methods:
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FIG. 1 Load Positions
6.2.11.1 Method 1 (Recommended for Single Range Balances)—Set the value to zero before measuring. Place the test load at
position 1 and then move to the other positions in sequence. The indication is recorded for each position.
6.2.11.2 Method 2 (Recommended for Multi-interval/Multiple Range Balances)—First place the test load in position 1 and
perform a tare operation on the balance. The test load is then moved sequentially to the other positions. The indication is recorded
for each position.
6.2.11.3 Method 3 (Recommended for Single Range Balances that Might Easily Show Drift)—Set the value to
...