ASTM E898-88(2013)
(Test Method)Standard Test Method of Testing Top-Loading, Direct-Reading Laboratory Scales and Balances
Standard Test Method of Testing Top-Loading, Direct-Reading Laboratory Scales and Balances
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.
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.
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Designation: E898 − 88 (Reapproved 2013)
Standard Test Method of Testing
Top-Loading, Direct-Reading Laboratory Scales and
Balances
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.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
Thismethodisdesignedtotestcommonlyusedlaboratoryscalesthatreadtheentirerangeofweight
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 other force is used to counterbalance the weight of the sample.
Otherforce-measuringdevicesmaybetestedbythismethodas
1.1 This test method covers the determination of character-
long as a sample placed on a receiving platform produces an
istics of top-loading, direct-reading laboratory scales and
indicationthatissubstantiallyalinearfunctionoftheweightof
balances. Laboratory scales of the top-loading type may have
the sample.
capacities from a few grams up to several kilograms. Resolu-
1.3 This standard does not purport to address all of the
tion may be from 1/1000 of capacity to 1/1000000 or more.
safety concerns, if any, associated with its use. It is the
This method can be used for any of these instruments and will
responsibility of the user of this standard to establish appro-
serve to measure the most important characteristics that are of
priate safety and health practices and determine the applica-
interest to the user. The characteristics to be measured include
bility of regulatory limitations prior to use.
the following:
1.1.1 warm-up,
2. Summary of Method
1.1.2 off center errors,
1.1.3 repeatability, reproducibility, and precision,
2.1 Throughout this method, the instrument is used in the
1.1.4 accuracy and linearity,
manner for which it is intended. One or more weights are used
1.1.5 hysteresis,
to test each of the characteristics, and the results are expressed
1.1.6 settling time,
intermsoftheleastcountorultimatereadabilityofthedisplay.
1.1.7 temperature effects,
1.1.8 vernier or micrometer calibration, and
3. Terminology
1.1.9 resistance to external disturbances.
3.1 Definitions of Terms Specific to This Standard:
1.2 Thetypesofscalesthatcanbetestedbythismethodare
3.1.1 accuracy—the degree of agreement of the measure-
of stabilized pan design wherein the sample pan does not tilt
ment with the true value of the quantity measured.
out of a horizontal plane when the sample is placed anywhere
3.1.2 capacity—the maximum weight load specified by the
on the pan surface. The pan is located generally above the
manufacturer. In most instruments, the maximum possible
measuring mechanism with no vertical obstruction, except for
reading will exceed the capacity by a small amount.
draft shields. Readings of weight may be obtained from an
3.1.3 full-scale calibration—the indicated reading when a
optical scale, from a digital display, or from a mechanical dial.
standard weight equal to the full scale indication of the scale is
Weighing mechanisms may be of the deflecting type, using
placed on the sample pan after the device has been correctly
gravityoraspringasthetransducer,ormaybeaforce-balance
zeroed. Usually some means is provided by the manufacturer
system wherein an electromagnetic, pneumatic, hydraulic, or
to adjust the full scale indication to match the weight of the
standard.
This test method is under the jurisdiction of ASTM Committee E41 on
Laboratory Apparatus and is the direct responsibility of Subcommittee E41.06 on
Weighing Devices.
Current edition approved Dec. 1, 2013. Published December 2013. Originally ANSI/ISA S51.1 “Process Instrumentation Technology”. Available from
approvedin1982.Lastpreviouseditionapprovedin2005asE898–88(2005).DOI: AmericanNationalStandardsInstitute(ANSI),25W.43rdSt.,4thFloor,NewYork,
10.1520/E0898-88R13. NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E898 − 88 (2013)
3.1.4 linearity—the degree to which a graph of weight 5. Apparatus
values indicated by a scale vs. the true values of the respective
5.1 Manufacturer’s Manual.
test weights approximates a straight line. For a quantitative
5.2 Standard Weights—A set of weights up to the capacity
statement of linearity errors, the concept of terminal-based
of the scale with sufficient subdivisions of weight so that
non-linearityisrecommended,suchas,themaximumdeviation
incrementsofabout10%ofthecapacityuptothecapacitycan
of the calibration curve (average of the readings at increasing
be tested.
and decreasing test load, respectively) from a straight line
drawnthroughtheupperandlowerendpointsofthecalibration 5.3 Thermometer, room temperature, with a resolution of at
curve.
least 1°C.
3.1.5 off-center errors—differences in indicated weight
5.4 Stop-Watch, reading to ⁄5 s.
when a sample weight is shifted to various positions on the
weighing area of the sample pan.
6. Preparation
3.1.6 hysteresis—difference in weight values indicated at a
6.1 Make sure that the scale and weights are clean.
given test load depending on whether the test load was arrived
6.2 Place the standard weights near the instrument.
at by an increase or a decrease from the previous load on the
6.3 Place the thermometer on the bench in such a position
scale.
that it can be read without being touched.
3.1.7 repeatability—closeness of agreement of the indicated
6.4 Allow the instrument and the weights to sit undisturbed
values for successive weighings of the same load, under
for at least 2 h with the balance turned off. Monitor the
essentially the same conditions, approaching from the same
temperatureduringthistimetomakesurethatthereisnomore
direction (such as, disregarding hysteresis).
than approximately 2°C variation over the last hour before
3.1.8 reproducibility—closeness of agreement of the indi-
beginning the test.
cated values when weighings of the same load are made over
a period of time under essentially the same conditions but not 6.5 Read the manufacturer’s instructions carefully. During
limited to the same direction of approach (such as, hysteresis each step of the test procedure, the instrument should be used
errors are included). in the manner recommended by the manufacturer. Know the
location of any switches, dials, or buttons as well as their
3.1.9 precision—the smallest amount of weight difference
functions.
between closely similar loads that a balance is capable of
detecting. The limiting factor is either the size of the digital
7. Test Procedure
stepoftheindicatorreadoutortherepeatabilityoftheindicated
values.
7.1 Warm-up Test:
7.1.1 If it is required in the normal operation of the scale to
3.1.10 standard deviation—used as a quantitative figure of
turn it “on” as an operation separate from weighing, perform
merit when making statements on the repeatability, reproduc-
that operation simultaneously with the starting of the stop-
ibility or precision of a balance.
watch.
3.1.11 readability—the value of the smallest unit of weight
7.1.2 If a zeroing operation is required, do it promptly.
that can be read without estimation. In the case of digital
Record the temperature.
instruments, the readability is the smallest increment of the
7.1.3 At the end of 1 min, read and record the indication
least significant digit (for example, 1, 2 or 5). Optical scales
with the pan empty.
may have a vernier or micrometer for subdividing the smallest
7.1.4 At the center of the sample pan place a standard
scale division. In that case, the smallest graduation of the
weight nearly equal to but not exceeding 98% of the capacity
vernier or micrometer represents the readability.
of the scale. If the scale allows no weight readings above the
3.1.12 standard weight—any weight whose mass is given.
stated nominal capacity, then this test should be performed
Since weights are not always available with documented
with standard weights equal to 90% of capacity. When the
corrections, weights defined by class may be used if the class
indication is steady, record the indication and remove the
chosen has sufficiently small limits and there is an understand-
weight from the pan.
ing that errors perceived as being instrumental in nature could
7.1.5 At the end of 5 min, repeat steps 7.1.3 and 7.1.4
be attributed to incorrectly adjusted weights.
without rezeroing.
7.1.6 At the end of 30 min, repeat again.
4. Significance and Use
7.1.7 At the end of 1 h, repeat again. Record the tempera-
ture.
4.1 Thismethodwillenabletheusertodevelopinformation
7.1.8 Compute for each measurement as follows:
concerning the precision and accuracy of weighing instru-
ments. In addition, results obtained using this method will k 5 W/ I 2 I (1)
~ !
t w o
permit the most advantageous use of the instrument. Weak-
where:
nesses as well as strengths of the instrument should become
I = indication with the standard weight on the pan,
w
apparent. It is not the intent of this method to compare similar
I = indication with pan empty,
o
instruments of different manufacture, but to enable the user to
W = known or assumed value of the standard weight, and
choose a suitable instrument.
E898 − 88 (2013)
Operation Weight on Pan Balance Reading
k = calibration factor for time t.
t
1 nil 0
7.1.9 Plot the values of k against the time (1 min, 5 min, 30
t
2 ⁄2 capacity W1
min, and 60 min). The time at which k apparently no longer
t
3 full capacity W2
drifts in one direction can be assumed to be the warm-up time 1
4 ⁄2 capacity W1'
5 nil Z
required.
7.1.10 If there is
...
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