1、Standard Specification for Weighing Devices Used in the Testing of Materials AASHTO Designation: M 231-95 (2015) American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-1b M 231-1 AASHTO Standard Specification for Weighing
2、 Devices Used in the Testing of Materials AASHTO Designation: M 231-95 (2015) 1. SCOPE 1.1. This specification covers requirements for scales and balances, and the loose standard masses used with balances, used in the testing of construction materials. 1.2. The requirements included are descriptive
3、of the balances required by a number of AASHTO test methods. The general-purpose balances described herein may not be sufficiently accurate for certain tests, especially where a high degree of accuracy is required at large capacities. In such instances, the requirements for the balance should be inc
4、luded in the test method. 1.3. The requirements included herein are not sufficiently descriptive to be used as purchase specifications without amplification by the potential purchaser. 1.4. The values stated in SI units are to be regarded as the standard. 2. REFERENCED DOCUMENTS 2.1. ASTM Standard:
5、E617, Standard Specification for Laboratory Weights and Precision Mass Standards 2.2. National Institute of Standards and Technology: NIST Handbook 44 (1992 Edition) 3. CLASSIFICATION 3.1. Weighing devices are divided into two classes of analytical balances, designated A and B, and five classes of g
6、eneral-purpose scales or balances, designated G1, G2, G5, G20, and G100, based on readability. 3.2. Standard masses classified as Class 1, 2, 3, and 4, listed in ASTM E617, Standard Specification for Laboratory Weights and Precision Mass Standards, may be used with the analytical balances. Standard
7、masses listed in Table 2, Section 2.23 of NIST Handbook 44 (1992 Edition) may be used with general-purpose balances. 4. TERMINOLOGY 4.1. acceptance tolerancethe maximum permissible deviation from correct indication for new standard masses or balances and for standard masses or balances having receiv
8、ed major servicing. Usually equal to one half of the maintenance tolerance. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b M 231-2 AASHTO 4.2. accuracymaximum permissible deviation of indications
9、of a balance or scale from the true value within applicable tolerances. 4.3. balancean instrument for determining mass, in its simplest form having a beam supported exactly in the middle and having two pans of equal mass suspended from its extremities. Generally, weighing devices of a relatively hig
10、h degree of accuracy used for determinations of mass in the laboratory. 4.4. direct-reading balancea balance on which the mass of applied loads of various magnitudes is either automatically indicated, or is indicated by means of a calibrated weighbeam, throughout all or a portion of the range of the
11、 balance. 4.5. equal-arm balancea balance having a beam supported exactly in the middle, having two pans suspended from its extremities, in which the mass of unknown quantity on one pan is compared with a set of standards of mass in the other pan. There may or may not be a weighbeam. 4.6. general-pu
12、rpose massesstandard masses used for general mass determination, generally being less accurate than standard analytical masses. 4.7. maintenance tolerancemaximum permissible deviation from correct indication for masses or balances in service. 4.8. off-center loadingapplication of a load to the pan o
13、f a balance or scale at a point displaced from the center of the support axis of the load-receiving element. 4.9. readabilitythe smallest unit of mass that can be read without estimation over the given range of measurement either directly or by use of a vernier or micrometer. 4.10. scalean instrumen
14、t or machine used for mass determination, usually embodying a system of multiplying levers. Generally considered to have a lesser degree of accuracy than balances. 4.11. sensitivitymass required to produce a discernible movement in the indicating system of the balance or scale. 4.12. sensitivity req
15、uirementthe minimum change in the position of rest of the indicating element of a scale or balance in response to a specified change in test load on the load-receiving element of the scale or balance. 4.13. simple balancea balance designed primarily for use in conjunction with a set of standard mass
16、es. There may or may not be a weighbeam. 4.14. standard analytical massesworking standards of mass used for analytical work, having relatively small tolerances from the stated values. 5. REQUIREMENTS 5.1. Analytical BalancesAnalytical balances of the class specified shall conform to the requirements
17、 of Table 1. These requirements apply both to balances with built-in masses and balances used with separate masses. The class for standard masses is suggested to provide the required accuracy (Note 1). 2015 by the American Association of State Highway and Transportation Officials.All rights reserved
18、. Duplication is a violation of applicable law.TS-1b M 231-3 AASHTO Table 1Standard Analytical Balances Balance Class Accuracy Sensitivity ReadabilityaClass of Standard MassesbCapacitycA 0.0002 g 0.0001 g 0.0001 g 1, 2, or 3 200 g B 0.002 g 0.001 g 0.001 g 3 200 g aReadability of markings on direct
19、reading balances. bClass suggested for use with simple balances. cMaximum capacity generally available with balances of the accuracy and sensitivity indicated for the class. Varies depending on the manufacturer, and whether direct reading or simple balance. Note 1The tolerances for standard masses a
20、re such that a single mass deviating by the full tolerance may cause the balance to exceed the accuracy requirement. In general, an individual mass will deviate only slightly from the stated value, and groups of masses will have some with a positive variation and some with a negative variation, whic
21、h will tend to be compensating. 5.2. General-Purpose Balances and ScalesGeneral-purpose weighing devices shall conform to the accuracy, readability, and sensitivity indicated in Table 2. Within any interval equal to 10 percent of the capacity of the balance, the difference in the load indications sh
22、all be accurate to within 0.1 percent of the difference in masses (Note 2). The device shall not be loaded in excess of its nominal or stated capacity. Table 2General-Purpose Balances and Scales Class Readability and Sensitivity AccuracyaG 1 0.01 g 0.02 g or 0.1 percent G 2 0.1 g 0.2 g or 0.1 percen
23、t G 5 1 g 2 g or 0.1 percent G 20 5 g 5 g or 0.1 percent G 100 20 g 20 g or 0.1 percent a Accuracy equal to the mass stated or 0.1 percent of the test load, whichever is greater, throughout the range of use. Note 2This requirement is to ensure linear performance of balance or scale. It is recommende
24、d that it be checked at five or more points throughout its range. 5.2.1. The balance selected for use is based on the accuracy, readability, sensitivity, and capacity required for the test being performed. Subportions of the sample are to be weighed to at least the accuracy indicated by the device r
25、equired for the total sample (Note 3). Note 3Balances have considerable variation in quality. Less expensive balances may be unable to provide the required accuracy for the full range of the capacity of the device, especially if subjected to rough field usage. 5.2.2. Balances indicating in the Avoir
26、dupois system (pounds and ounces), or separate masses used with such devices, shall meet levels of accuracy, readability, and sensitivity equivalent to those shown in Table 2 for balances and Table 4 for masses. 5.3. Balance ConditionThe physical design and condition of a balance shall be such that
27、the balance will meet the requirements of Sections 5.1 and 5.2. 5.3.1. Repeated determinations of the mass of a test load shall yield load indications that agree with each other within the sensitivity specification for the balance. 5.3.2. Mechanisms for adding or subtracting built-in internal masses
28、 shall function smoothly. 5.3.3. Dials and mass increment indicators shall display clearly the readings they were designed to show. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b M 231-4 AASHTO 5.
29、3.4. The accuracy requirement shall be met for any point of application of a test load on the balance pan or other mass receiving element. 5.4. MassesMasses shall be selected so that the requirements for accuracy, sensitivity, and/or readability specified in Sections 5.1 and 5.2 are met when the mas
30、ses are used with the appropriate balance. 5.4.1. Standard Analytical BalancesAnalytical masses for use with equal arm balances should be Class 1, 2, 3, or 4, as appropriate for the accuracy of the balance with which they are to be used. The requirements for these masses are described in ASTM E617.
31、Applicable tolerances are shown in Table 3. Class 1 and 2 masses are reference masses, generally used for verification of masses of lesser classes, although Class 2 masses are used as working masses for high-precision mass determinations. Classes 3 and 4 are considered to be working masses (Note 1).
32、 Table 3Tolerances for Standard Analytical Masses Acceptance Tolerances Class 1aClass 2bTolerance Tolerance Class 3cClass 4cDenomination Individual, mg Group, mg Individual, mg Group, mg Tolerance, mg Tolerance, mg 1000 g 2.5 5.0 10.0 20.0 500 g 1.2 2.5 5.0 10.0 300 g 0.75 1.35 1.5 2.7 3.0 6.0 200 g
33、 0.50 1.0 2.0 4.0 100 g 0.25 0.50 1.0 2.0 50 g 0.12 0.25 0.60 1.2 30 g 0.074 0.16 0.15 0.29 0.45 0.90 20 g 0.074 0.10 0.35 0.70 10 g 0.050 0.074 0.25 0.50 5 g 0.034 0.054 0.18 0.36 3 g 0.034 0.054 0.15 0.30 2 g 0.034 0.065 0.054 0.105 0.13 0.26 1 g 0.034 0.054 0.10 0.20 500 mg 0.010 0.025 0.080 0.16
34、 300 mg 0.010 0.025 0.070 0.14 200 mg 0.010 0.020 0.025 0.055 0.060 0.12 100 mg 0.010 0.025 0.050 0.10 50 mg 0.010 0.014 0.042 0.085 30 mg 0.010 0.014 0.038 0.075 20 mg 0.010 0.020 0.014 0.034 0.035 0.070 10 mg 0.010 0.014 0.030 0.060 5 mg 0.010 0.014 0.028 0.055 3 mg 0.010 0.014 0.026 0.052 2 mg 0.
35、010 0.020 0.014 0.034 0.025 0.050 1 mg 0.010 0.014 0.025 0.050 a Maintenance tolerances same as acceptance tolerances. b Maintenance tolerances for standard masses below 100 mg are the same as acceptance tolerances. For standard masses 100 mg and above, the maintenance tolerances are twice the accep
36、tance tolerances. c Maintenance tolerances are twice the acceptance tolerances. 5.4.2. General-Purpose MassesGeneral-purpose masses for use with equal arm balances should conform to the requirements of NIST Handbook 44 (1992 Edition), Table 2, Section 2.23, Weights. Masses for use with single pan ba
37、lances shall have sufficient accuracy so that the balances meet the requirements for such devices. Applicable tolerances are shown in Table 4. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b M 231-
38、5 AASHTO Table 4Tolerances for General-Purpose Masses Denomination Maintenance ToleranceaDenomination Maintenance Tolerancea20 kg 1500 mg 30 g 30 mg 10 kg 1000 mg 20 g 20 mg 5 kg 800 mg 10 g 15 mg 3 kg 500 mg 5 g 10 mg 2 kg 400 mg 3 g 8 mg 1 kg 250 mg 2 g 6 mg 500 g 175 mg 1 g 4 mg 300 g 150 mg 500
39、mg 3.0 mg 200 g 100 mg 300 mg 2.0 mg 100 g 70 mg 200 mg 1.5 mg 50 g 40 mg 100 mg 1.0 mg a Acceptance tolerances on new masses are one half of the maintenance tolerances. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.
