1、Standard Practice for Establishing Requirements for Equipment Calibrations, Standardizations, and Checks AASHTO Designation: R 61-12 (2016)1Release: Group 1 (April 2016) American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001
2、 TS-5c R 61-1 AASHTO Standard Practice for Establishing Requirements for Equipment Calibrations, Standardizations, and Checks AASHTO Designation: R 61-12 (2016)1Release: Group 1 (April 2016) 1. SCOPE 1.1. This practice contains general criteria and guidelines for establishing requirements for equipm
3、ent calibrations, verification of calibrations, standardizations, and checks. This practice is intended to be used for equipment and test methods not specifically addressed in R 18. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: R 18, Establishing and Implementing a Quality Management System for Con
4、struction Materials Testing Laboratories T 176, Plastic Fines in Graded Aggregates and Soils by Use of the Sand Equivalent Test T 201, Kinematic Viscosity of Asphalts (Bitumens) T 245, Resistance to Plastic Flow of Asphalt Mixtures Using Marshall Apparatus 2.2. International Standards: International
5、 Vocabulary of MetrologyBasic and General Concepts and Associated Terms (VIM), Third Edition. International Organization for Standardization, Joint Committee for Guides on Metrology, Svres, France, 2008. ISO 5725-1, Accuracy (Trueness and Precision) of Measurement Methods and Results Part 1: General
6、 Principles and Definitions ISO/IEC 17025, General Requirements for the Competence of Testing and Calibration Laboratories. Evaluation of Measurement DataGuide to the Expression of Uncertainty in Measurement (GUM). International Organization for Standardization, Joint Committee for Guides on Metrolo
7、gy, Svres, France, 2008. The U.S. edition of the GUM is entitled American National Standard for Expressing UncertaintyU.S. Guide to the Expression of Uncertainty in Measurement, ANSI/NCSL Z540-2-1997 (R2012). 3. TERMINOLOGY 3.1. accuracy of measurementcloseness of the agreement between the result of
8、 a measurement and a true value of the measurand (VIM, Section 3.5). 3.1.1. DiscussionPart 1 of the international standard ISO 5725-1 on the accuracy of measurement methods and results defines accuracy as the closeness of agreement between a test result and the accepted reference value. This definit
9、ion is supplemented by a note that states that the term “accuracy,” when applied to a set of test results, involves a combination of random components 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-
10、5c R 61-2 AASHTO and a common systematic error or bias component. Accuracy is thus viewed as a characteristic of a measurement process consisting of precision as well as bias components. A process is considered to be accurate only if it is precise as well as unbiased. The expanded uncertainty of a m
11、easurement, discounting the bias, is equivalent to the accuracy of the measurement after a correction or correction factor is applied. 3.2. calibration, na set of operations that establish, under specified conditions, the relationship between values of quantities indicated by a measuring instrument
12、or measuring system, or between values represented by a material measure or a reference material, and the corresponding values realized by standards (VIM, Section 6.11). 3.2.1. ExampleBalances (measurement instrument), Dynamic Shear Rheometer (measuring system), Pycnometer (material measure). 3.2.2.
13、 DiscussionThe purpose of calibration is to ensure that measurements made by the laboratory are traceable to the International System of Units (SI). Where traceability of measurements to SI units is not possible or relevant, measurements must be traceable to certified reference materials, agreed met
14、hods, or consensus standards. Uncertainty estimates obtained during calibration are used to judge if an instrument is suitable for its intended purpose. There is a need to reestablish traceability or recalibrate only when instrument measurements drift out of control as determined through verificatio
15、n of calibration (Section 3.10). 3.3. check, na specific type of inspection and/or measurement performed on the physical properties of equipment and materials to determine compliance or otherwise with stated criteria. 3.4. correction, nvalue added algebraically to the uncorrected result of a measure
16、ment to compensate for systematic error (VIM, Section 3.15). 3.4.1. DiscussionBecause the systematic error cannot be known perfectly, the correction can only be an estimate. 3.5. correction factor, nnumerical factor by which the uncorrected result of a measurement is multiplied to compensate for sys
17、tematic error (VIM, Section 3.16). 3.5.1. DiscussionBecause the systematic error cannot be known perfectly, the correction factor can only be an estimate. 3.6. standard, nmaterial measure, measuring instrument, reference material, or measuring system intended to define, realize, conserve, or reprodu
18、ce a unit of one or more values of a quantity to serve as a reference (VIM, Section 6.1). 3.7. standardization, na process that determines (1) the correction or correction factor to be applied to the result of a measuring instrument, measuring system, material measure, or reference material when its
19、 values are compared to the values realized by standards, (2) the adjustment to be applied to a piece of equipment when its performance is compared with that of an accepted standard or process. 3.7.1. DiscussionStandardization in case (1) is a simplified form of calibration that estimates systematic
20、 error but does not identify random error. Standardization, therefore, does not address all of the elements of uncertainty of measurement and does not lead to traceable measurements. An example of case (2) standardization is adjusting the number of blows of a mechanically operated hammer so it appli
21、es the energy equivalent to that of a manually operated hammer. 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-5c R 61-3 AASHTO 3.8. traceability, nthe property of the result of a measurement or the
22、 value of a standard whereby it can be related to stated references, usually national or international standards, through an unbroken chain of comparisons all having stated uncertainties (VIM, Section 6.10). 3.8.1. DiscussionThere is a need for traceable measurements. Measurements, not the instrumen
23、t, can be traceable. Measurement traceability is established through calibration. Measurement traceability is maintained through verification of calibration (a regular check of instrument output using a control standard). 3.9. uncertainty of measurement, nparameter, associated with the result of a m
24、easurement, that characterizes the dispersion of the values that could reasonably be attributed to the measurand (VIM, Section 3.10). 3.9.1. DiscussionThe uncertainty of a measurement is required in order to establish its traceability. An evaluation of the uncertainty of measurement is conducted to
25、determine if measurement equipment is fit for purpose. The expanded uncertainty of a measurement, discounting the bias, is equivalent to the accuracy of the measurement after a correction or correction factor is applied. 3.9.2. The definitions of various uncertainty terms used in the GUM are: Standa
26、rd uncertaintyuncertainty of the result of a measurement expressed as a standard deviation. Combined standard uncertaintystandard uncertainty of the result of a measurement when that result is obtained from the values of a number of other quantities, equal to the positive square root of the sum of t
27、he terms, the terms being the variances or covariance of these other quantities weighed according to how the measurement result varies with change in these quantities. Expanded uncertaintyquantity defining an interval about the result of a measurement that may be expected to encompass a large fracti
28、on of the distribution of values that could reasonably be attributed to the measurement. Coverage factornumerical factor used as a multiplier of the combined standard uncertainty in order to obtain an expanded uncertainty. The coverage factor k is typically in the range of 2 to 3. 3.10. verification
29、 of calibration, na process that establishes whether the results of a previously calibrated measurement instrument, measurement system, material measure, or reference material are in control. 3.10.1. DiscussionVerification of calibration is used to maintain the traceability of a measurement and to d
30、etermine when to recalibrate. Control charts should be used to plot verification results and determine if instrument measurements have drifted out of control. 3.11. verification of standardization, na process that establishes whether the results of a previously standardized measurement instrument, m
31、easurement system, material measure, or reference material are in control. 3.11.1. DiscussionVerification of standardization is used to indicate when a shift in the population average occurs and when it is time to restandardize. Control charts should be used to plot verification results and determin
32、e if instrument measurements have drifted out of control. 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-5c R 61-4 AASHTO 4. SIGNIFICANCE AND USE 4.1. Construction material test standards can be imp
33、roved if equipment calibrations, standardizations, and checks are properly specified and if each activity and its requirements are understood. 4.2. The guidance in this document is intended to be used by standards developers in the selection of terms used in methods and in the establishment of appro
34、priate requirements for equipment calibrations, standardizations, and checks. 4.3. The guidance in this document can also be used by laboratories for performing equipment calibrations, standardizations, and checks. 5. GUIDANCE FOR STANDARDS DEVELOPERS 5.1. Calibration or Standardization versus Check
35、ingMost measuring instruments, measuring systems, and material measures should be either calibrated or standardized. Checking applies to test equipment that is not a measuring instrument, measuring system, or material measure such as an oven, straightedge, or specimen mold. 5.2. Determining if Equip
36、ment Checks Are NecessaryThe primary consideration in deciding whether a piece of test equipment should be checked is the equipments influence on the test result. If the physical properties of a piece of equipment could significantly influence the test result, then routine checks to determine compli
37、ance or otherwise with stated criteria are essential. However, if the physical properties of a piece of test equipment are not likely to affect the test result, routine equipment checks are not necessary. 5.3. Calibration versus StandardizationThe two primary considerations for making the decision t
38、o calibrate or standardize a measuring instrument, measuring system, or material measure are (1) the measurements influence on the test result and (2) the probability that the uncertainty of measurement could exceed the accuracy requirement of the measurement. Refer to Figure 1 for guidance for dete
39、rmining whether to specify equipment calibration, standardization, or nothing. Probability That the Uncertainty of Measurement Could Exceed the Accuracy Requirement of the Measurement Low Moderate High MeasurementsInfluence onthe TestResultHighStandardize Calibrate Calibrate ModerateStandardize Stan
40、dardize Calibrate LowNothing Standardize Standardize Figure 1Guidance for Determining Whether Equipment Shall Be Calibrated, Standardized, or Neither 5.4. Selecting and Specifying Intervals for Equipment Calibrations, Standardizations, and ChecksEquipment calibration, standardization, and check inte
41、rvals shall be specified in the test methods (Notes 1 and 2). The two primary considerations for determining an acceptable interval are (1) the probability that time and/or usage will affect the instrument or device and (2) the measurements 2016 by the American Association of State Highway and Trans
42、portation Officials. All rights reserved. Duplication is a violation of applicable law.TS-5c R 61-5 AASHTO or devices influence on the test result. Refer to Table 2 for guidance for determining intervals between calibrations, standardizations, and checks. Note 1When the risk associated with using in
43、accurate equipment or nonconforming equipment is high, equipment should be monitored frequently. When the risk is low, less frequent monitoring may suffice. Note 2Because the user may have verification of calibration data to support extending a calibration interval beyond the interval specified, the
44、 following wording is suggested for use when specifying calibration intervals: “In the absence of verification of calibration data to support the extension of the interval between calibrations, the interval between calibrations shall not exceed _ months.” Probability That Time or Usage Will Affect t
45、he Instrument/Device Low Moderate High MeasurementsInfluence onthe TestResultHighMonitoring (Moderate Risk) Frequent Monitoring (High Risk) Frequent Monitoring (High Risk) ModerateInfrequent Monitoring (Low Risk) Moderate Monitoring (Moderate Risk) Frequent Monitoring (High Risk) LowInfrequent Monit
46、oring (Low Risk) Infrequent Monitoring (Low Risk) Moderate Monitoring (Moderate Risk) Figure 2Determining the Interval between Equipment Calibrations, Verification of Calibrations, Standardizations, and Checks Note 3Intervals for frequent monitoring should be between 1 month and 4 months; intervals
47、for moderate monitoring should be between 4 and 12 months; intervals for infrequent monitoring should be between 12 and 24 months. 6. GUIDANCE FOR LABORATORIES THAT CHOOSE TO EXTEND CALIBRATION OR STANDARDIZATION INTERVALS BEYOND THE INTERVALS SPECIFIED IN STANDARDS 6.1. GeneralA laboratory may use
48、the calibration and standardization intervals specified in a standard or may extend calibration and standardization intervals beyond the intervals specified in the standards. To extend calibration and standardization intervals beyond those specified, a laboratory must establish and implement a progr
49、am for continual verification of equipment calibrations and standardizations. 6.2. Appendix X1 gives an example of an acceptable “verification of calibration” program. A “verification of standardization” program would be similar to the “verification of calibration” program. 7. REQUIREMENTS FOR LABORATORIES PERFORMING CALIBRATIONS, STANDARDIZATIONS, AND CHECKS 7.1. General (the Risk)When the results of equipment calibrations, standardizations, or checks indicate that the equipment is out of conformance with s
