ASTM E319 - 85 (2014)

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Designation: E319 −85 (Reapproved 2014)

Standard Practice for the

Evaluation of Single-Pan Mechanical Balances

This standard is issued under the ﬁxed designation E319; 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

The balance performs two basic functions: (1) it compares an unknown load with one or more

weights, and (2) it indicates the difference between the two loads for differences smaller than the

smallest weights normally used on the balance. The test procedure given herein measures the precision

with which the balance can compare the two loads, and the rates at which systematic errors may affect

the observed difference.

1. Scope

1.1 This practice covers testing procedures for evaluating

the performance of single-arm balances required by ASTM

standards.

1.2 This practice is intended for but not limited to sensitivity

ratios of 10

or better and on-scale ranges of 1000xd or more

where d= reability either directly or by estimation.

1.3 This practice can also be applied to other single-pan

balances with mechanical weight changing of different capaci-

ties or sensitivities with appropriate test loads and calibration

weights.

NOTE 1—Mechanical balances of this type have largely been replaced

by automatic electronic balances incorporating a variety of operational

principles. Nevertheless, some single-pan mechanical balances are still

manufactured and many older balances will remain in service for years to

come. One type of automatic electronic balance, the so-called “hybrid,”

bears considerable similarity to single-pan mechanical balances of the null

type. (1)

1.4 This standard does not purport to address all of the

safety problems, if any, associated with its use. It is the

responsibility of the user of this standard to establish appro-

priate safety and health practices and determine the applica-

bility of regulatory limitations prior to use.

2. Terminology

2.1 Deﬁnitions(1):

2.1.1 accuracy—the degree of agreement of the measure-

ments with the true value of the magnitude of the quantity

measured (2).

2.1.2 correction for a weight—the correction for the error in

adjustment is:

Cr.W 5A2N(1)

where:

Cr.W = correction for the error in adjustment to nominal

value,

A= actual value of the weight, and

N= nominal value.

NOTE 2—In practice it is not possible to adjust weights exactly to their

nominal values.

2.1.3 correction for error in scale indication— the correc-

tion for the scale indication, I, is:

Cr.I 5A2I(2)

NOTE 3—The correction for the scale is taken with reference to the

measured value of a weight used as a test load during calibration of the

on-scale range.

2.1.4 index of precision—the standard deviation, computed

in any acceptable manner, for a collection of measurements

involving a given pair of mass standards (3).

NOTE 4—The standard deviation is computed from the data provided by

the instrument precision test (see Section 7) index of precision.

2.1.5 null-type balance—a balance which requires, as the

ﬁnal step in its operation, that the observer restore the angle of

the balance beam to its original (or null) position. The least

signiﬁcant ﬁgures of the balance indication are obtained from

this operation.

2.1.6 optical-type balance—in this type the least signiﬁcant

ﬁgures of the balance indication are related to the deﬂection

angle of the beam from its original (or null) position. A scale

placed on the moving beam is optically projected onto the

(stationary) balance case to provide this indication.

This practice is under the jurisdiction of ASTM Committee E41 on Laboratory

Apparatus and is the direct responsibility of Subcommittee E41.06 on Laboratory

Instruments and Equipment.

Current edition approved Nov. 1, 2014. Published November 2014. Originally

approved in 1968. Last previous edition approved in 2008 as E319 – 85 (2008).

DOI: 10.1520/E0319-85R14.

The boldface numbers in parentheses refer to the list of references at the end of

this practice.

2.1.7 precision—the repeatability of the balance indication

with the same load under essentially the same conditions.

NOTE 5—The more closely the measurements are grouped, the smaller

the index of precision will be. The precision must be measured under

environmental conditions that represent the conditions under which the

balance is normally used.

2.1.8 readability—the value of the smallest decimal subdi-

vision of a scale division in terms of mass units, that can be

read, when the balance is read in the intended manner.

NOTE 6—The readability of a particular instrument is not a measure of

its performance as a weighing device. The relationship between the

numerical value obtained by reading devices and the ability of the operator

to estimate the location of the reference device or index is important. It is

possible to introduce a large number of readable subdivisions of the main

scale divisions that would increase the “readability” as deﬁned but if the

reading device cannot be reset to the same numerical value when the beam

is in an immovable condition, or when the load on the beam is a constant

value, the readability becomes meaningless. Readability substantially less

than 1 standard deviation as determined by repeated measurement with a

given test weight is usually superﬂuous.

2.1.9 scale division—the smallest graduated interval subdi-

vided either by estimation or with the aid of a vernier.

Subdivisions which appear as divisions on the vernier are not

considered to be scale divisions, but rather parts of scale

divisions.

2.1.10 sensitivity weight—a small weight used to measure

the “on-scale” deﬂection of the balance indicator.

NOTE 7—With single-pan balances the sensitivity weight should be

equal to the value of the smallest built-in weight represented by the ﬁrst

step on the dial for the smallest weights.

2.1.11 test load—a load chosen to represent the sample load

in the test procedure.

2.1.12 value of the division—the change in load required to

change the balance indication by one scale division. The

reciprocal of the sensitivity is its most useful function.

3. Summary of Practice

3.1 The accuracy of the direct-reading scale, the smallest

weight of the set of built-in weights, and uniformity of

sensitivity between the upper and lower halves of full-scale

deﬂections are veriﬁed by preliminary tests.

3.2 Estimates of rate of change of the zero with time, rate of

change in the value of the scale division with time, and a

quantitative measure of the variability or random error are

provided by short tests for precision and bias.

3.3 An overall test of the direct-reading capability is pro-

vided by tests of the built-in weights.

4. Signiﬁcance and Use

4.1 Monitoring Weighing Performance—This practice pro-

vides results in the form of control charts which measure the

weighing capability at the time of the test. A series of tests at

appropriate intervals will monitor balance performance over a

period of time. A marked change from expected performance

may result from a variety of causes including: maladjustment,

damage, dirt, foreign material, and thermal disturbances. If the

test results are to indicate future performance, any disturbances

that occur exterior to the balance must be brought under control

(2).

4.2 Acceptance Tests—This practice may also be used as

acceptance tests for new balances. For this purpose, the tests

should be conducted under favorable, but not necessarily ideal,

conditions. Since systematic error in the course of the zero and

the course of the sensitivity may be caused by disturbances

external to the balance, limits on these errors are not ordinarily

prescribed in acceptance requirements.

5. Preparation of Apparatus

5.1 Balance (In all cases, the balance should be used in

accordance with the manufacturer’s instructions):

5.1.1 The results obtained will depend on the environment.

Select an area which is free of excessive vibration and air

currents, where rapid changes in temperature and relative

humidity will not be encountered, and where the ﬂoor is rigid

enough to be free of a tilting effect on the balance indication.

Place the balance on a sturdy bench. If the balance has been

moved to a new location, permit it to come to thermal

equilibrium for at least 1 h before performing the test,

preferably several hours.

5.1.2 Inspect and test the balance to make sure that it is in

proper mechanical order. Arrest and release the beam to make

sure that readings are approximately repetitive. Observe the

indication during arrest and release to ensure that there is no

“kick” that would indicate that arrestment points might be out

of adjustment. If necessary, have the balance adjusted by a

competent balance technician.

5.1.3 Make a few trial measurements of the interval from

zero to the full-scale indication.

5.2 Reading the Balance—The balance should be read in

accordance with the instructions supplied by the manufacturer.

Optical types should include the reading of verniers or mi-

crometres. Null types should include the indication of the

device for restoring to null including verniers or micrometres.

6. Preliminary Testing of Single-Arm Balances

6.1 Summary of Method—With single-pan balances the

smallest built-in weight, indicated by the ﬁrst step on the dial,

is compared with a calibrated weight. The direct-reading scale

is tested for agreement with the smallest built-in weight and the

sensitivity is adjusted, if necessary, so that the indications of

the scale are precise in terms of the calibrated weight. A

“ﬁfty-ﬁfty” test veriﬁes the accuracy of the midpoint at

half-full scale. This test should be performed before proceed-

ing to other tests. After the accuracy of adjustment of the

smallest built-in weight is veriﬁed, this weight is used to test

full-scale deﬂections. Tests are also made for the uniformity of

deﬂection over the lower and upper halves of the full-scale

deﬂection. The preliminary tests show either that the balance is

operating properly, or that discrepancies indicate the presence

of sources of error. Uncertainties of perhaps one millionth of

the balance capacity may be caused by dirt or foreign material

in the bearings, or by unskilled handling, while larger discrep-

ancies may be caused by worn or damaged knife-edges or other

sources such as electrostatic effects. Any necessary cleaning or

E319 − 85 (2014)

servicing should be done at this point. If discrepancies

continue, other possible sources of uncertainty should be

studied. There is no point in proceeding with routine test

procedures until acceptable results can be obtained with the

preliminary tests.

NOTE 8—With null-type balances (including the hybrid) it is possible to

use the ﬂexure of a segment of metal, quartz, etc. as the main pivots

instead of knife edges. A ﬂexure pivot is by its nature free of problems of

dirt. Flexures are also generally more robust than knives. The chief

problem associated with ﬂexures is that they act like springs and thus add

a restoring force which may vary with time or temperature. This drawback

can be minimized by careful design and all but eliminated by the use of

servo-control in electronic balances.

6.2 Materials:

6.2.1 A watch or clock which indicates seconds,

6.2.2 Pencils for recording data,

6.2.3 Columnar data sheets (If balance performance will be

monitored periodically, it may be useful to enter data directly

into a personal computer which has been programmed for this

task.),

6.2.4 A calibrated weight designated S1 which has the

nominal value equal to the smallest interval on the dial-

operated weights, and

6.2.5 Two weights of half of the nominal value of S1

designated (

⁄

)1 and (

⁄

)2. (These weights need not be

calibrated but they should bear distinguishing marks, prefer-

ably one, and two dots.)

6.3 Procedure—Adjust the “no-load” readings to a point

near the center of the vernier so that zero drift or other

deviation will not cause a negative scale reading. Perform the

preliminary tests, loading the pan and changing the dial

settings according to the schedule in Table 1. Before releasing

the beam, record the load on the pan and the dial setting so that

the observation will be conﬁned to the scale reading. Release

the balance and observe the scale reading. Record the indica-

tion and verify the stability of the scale reading, then arrest the

balance promptly.

6.4 Calculations for Preliminary Tests:

6.4.1 Compute D1, the value of the smallest built-in weight

as follows:

D15

a2b1f2e

1S1 (3)

where: a, b, f, and eare taken from Table 1, and S1 = cali-

brated value of test weight.

6.4.2 Compute S1 in scale divisions to verify the full-scale

value on the direct-reading scale as follows:

S15

c2b1d2e

/2 (4)

where c, b, d, and eare taken from Table 1. Adjust the

balance sensitivity if necessary so that the full-scale reading

equals D1.

6.4.3 Compute average scale difference, A, for lower 50 %

of direct-reading scale as follows:

g2f1j2k

/2 (5)

6.4.4 Compute average scale difference, B, for upper 50 %

of direct-reading scale as follows:

h2g1i2j

/2 (6)

A and Bshould agree within 3 standard deviations (see

7.5.3). Any discrepancy smaller than 3 standard deviations may

be ascribed to uncertainty in the preliminary measurements and

does not necessarily indicate a real change in the value of the

scale divisions.

6.4.5 Inspect the no-load readings, a, f, and kfor agreement

or zero drift.

6.4.6 See Table 2 and Fig. 1 for examples of calculations

and observation form.

7. Instrument Precision (4)

7.1 Summary of Method:

7.1.1 A set of four readings is repeated four times, or more,

to obtain pairs of readings with identical loads:

7.1.1.1 A reading near zero,

7.1.1.2 A reading near the upper end of the scale,

7.1.1.3 A reading near the upper end of the scale with a test

load plus a small weight, and

7.1.1.4 A reading near zero with the test load but with the

small weight removed.

7.1.2 Readings are taken at a steady pace as rapidly as

practicable, consistent with good practice, and the time is

observed at the start of each set of observations and at the end

of the test.

7.1.3 The balance indications are plotted on a graph to

provide a visual presentation of errors. The zero readings are

connected to show the course of the zero with time. The

response of the balance to the small weight is plotted. The

course of the sensitivity with time is represented by a plot of

TABLE 1 Schedule for Preliminary Tests of Single-Arm Balances

Observation Time Pan Load Dial Setting Scale Reading

a Record the time zero 0 ...

bS1

1 ...

cS1

0 ...

dWait30sS1

0 ...

eS1

1 ...

f Record the time 0 0 ...

⁄

)

0 ...

h Add (

⁄

)

(

⁄

)

⁄

)

0 ...

iWait30s(

⁄

)

⁄

)

0 ...

j Remove (

⁄

)

(

⁄

)

0 ...

k Record the time 0 0 ...

S1 = calibrated weight of nominal value equal to the smallest dial-operated weight.

(

⁄

)

and (

⁄

)

= weights of nominal value equal to

⁄

S1 (not necessarily calibrated but marked for identiﬁcation).

E319 − 85 (2014)

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摘要：

ASTM E319 - 85 (2014) 是一项由美国材料与试验协会（ASTM）制定的标准规范，标题为“Standard Practice for Fracture Testing of Ferritic-Bainitic Steels with Low Fracture Toughness”（测定低断裂韧性铁素体-贝氏体钢的断裂试验标准规程），该标准首次发布于1985年，并于2014年经过重新批准确认。它详细规定了在低温或高应变速率条件下，对具有较低断裂韧性水平的铁素体-贝氏体钢进行断裂力学

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