ASME B89.7.6 pdf download

ASME B89.7.6 pdf download.Guidelines for the Evaluation of Uncertainty of Test Values Associated With the Verification of Dimensional Measuring Instruments to Their Performance Specifications.
ASME B89.7.6 provides guidelines for evaluating the uncertainty of test values obtained when verifying dimensional measuring instruments’ to an ASME 889 testing protocol. The scope is limited to the case in which the test measurand is the error of indication at a rated operating condition; hence, Lest measurands such as the “worst possible” error of indication that might occur at any operating condition (including those conditions that are not tested) are outside the scope of this Standard.
ASME B89 testing protocols are composed of many individual tests, each test yielding one test value that is an estimate of the instrument’s measurement error at the particular operatrng condition tested, and this test value is compared against the maximum permissible error (M PE) (specified for that rated operating condition) using the protocol’s decision rule. Although the MPE is specified by the Instrument manufacturer for all rated operating conditions, the test value uncertainty is associated only with the test value obtained at the particular operating condition prevailing at the moment the test value was obtained (unless a correction to the indication is performed that is allowed by the test protocol).
Because each test investigates the error of indication at a particular rated operating condition, the test value uncertainty does not include the robustness or comprehensiveness of the testing protocol, i.e., it does not address the number of tests or their distribution over different rated operating conditions. This issue is addressed by the standardization committee creating the testing protocol; the committee balances the number of tests against the amount of time and effort to complete the testing protocol.
The scope of this Standard excludes issues associated with the evaluation of the uncertainty of future measurement results on workpleces and focuses solely on the Lest value uncertainties used to verify the instruments performance specification. Typically, the test value uncertainty is much smaller than the associated MPE value of the verification test.
2 DEFINITIONS
The following definitions are specific to this Standard:
instrument. the measuring system that is under verification to its performance specification.
NOTE: In this Standard, the term instrurnent is equivalent to instrurnent under vertflcation.
verification system: the measuring system that is used to verify an instrument to its performance specification.
NOTE: In this Standard, the verification system includes everything necessary to execute the testing protocol. This includes the calibrated reference quantity, equipment used in the transfer process, the human operator (if one is involved), computations and any other analysis needed, environmental and other conditions required by the instrument under verification, and any input quantities required to realize the measurand of the verification test.
3 REFERENCES
The following is a list of publications referenced in this Standard:
ASME B891.13-2013, Micrometers
ASME B89.1,14-2018, Calipers
ASME B89.4.10360.2-2008, Acceptance Test and Reverification Test for Coordinate Measuring Machines (CMMs) — Part 2: CMMs Used for Measuring Linear Dimensions (Technical Report)
A-2 REFERENCE STANDARD CALIBRATED VALUE
(a) Included in Test Value Uncertainty. The reference value is obtained from a gauge block whose length is uncertain by an amount stated on its calibration certificate, i.e., the true value of the reference length is uncertain. Dividing the expanded uncertainty (shown on the gauge block calibration report) by the coverage factor (e.g., k = 2) yields the standard uncertainty of 0,25 pin. Since this gauge block has been recalibrated several times and it consistently yields the same calibrated value (within the 0.5-pm calibration uncertainty), there is no additional uncertainty due to dimensional instability of the block, and hence the reference value of the gauge block at the time of’ testing is taken to be its calibrated value with the uncertainty shown on the calibration report.
(b) Not Included in Test Value Uncertainty. No additional test value uncertainty is allowed for the accuracy of the scales in the CMM as they are part of the system under test and their inaccuracies will appear as an error of Indication, which Is subject to the MPE specification being tested.
A-3 REPRODUCIBILITY AND RESOLUTION OF THE REFERENCE STANDARD
‘a) Included in Test Value Uncertainty. Any influence that causes the reference value of the gauge block, at the moment it Is presented to the CMM underveriflcatlon, to vary from Its calibrated value Is an uncertainty contributor. In this example, an analysis of the fixturing holding the gauge block determines it is vibrating slightly due to excitations from the CMM motion. Since the rated operating conditions (required for the MPE) require a rigid reference standard, this is an uncertainty source; it is estimated to have a standard uncertainty of 0.1 pm. The resolution of the measuring system (the gauge block) is determined by the last digit shown on the gauge block calibration report. Since it is common practice to report the gauge block length with more precision than its associated uncertainty, this source is negligible.