ASME B1.25-2019 pdf download

ASME B1.25-2019 pdf download.Measurement Uncertainty Factors in the Calibration of Screw Thread Gages.
Optical comparators and similar devices may have specially designed accessories for measuring linear pitch, but their overall performance is limited compared to that of instruments designed for such work.
5 FACTORS TO BE INCLUDED IN UNCERTAINTY BUDGETS
Fvery factor that could affect a particular measurement should be included in the uncertainty budget or statement for the measurement. It is recommended that even a factor of little significance be included because its inclusion will assure anyone reviewing the uncertainty midget that all factors have been considered.
Similarly, multiple readings for each measurement help to quantify the effects of some of the factors. From a commercial point of view, however, this ideal is rarely realized due to the costs involved. A typical commercial laboratory takes only a single reading for each measurement location on a gage, whereas a NIST laboratory or another National Measurement Institute facility takes multiple measurements and generates statistically significant values for a factor. The lab values therefore have a lower level uncertainty than do the commercial laboratory’s values. The factors noted in this section assume that a single reading for each measurement will be treated mathematically using statistically derived divisors or multipliers with that situation in mind.
5.1 Common Factors
5.1.1 Temperature. All dimensional measurement results are considered valid at the standard reference temperature of 68°F (20°C). Measurements taken at other temperatures are acceptable if they are corrected for the deviation from the standard reference temperature. Alternatively, the uncertainty budget could include a factor for large variations from the standard temperature. A footnote to the uncertainty statement should indicate that if the alternative is chosen, that fact should be noted in the budget.
An uncertainty budget must include known temperature variations arid errors in the thermometry used to determine them. Typically, the finer the resolution of the measurement or the larger the item being measured, the greater the effects of the temperature variations.
5.1.2 RepeatabiLity and Resolution. The typical uncertainty budget includes either the repeatability or the resolution of the measurement process, whichever of these elements has the higher variation. Usually, resolution is much finer than repeatability, and so repeatability is the element that appears in the uncertainty budget.
It should be noted that repeatability refers to the repeatability of the overall process and not just to that of the measuring device. While the overall repeatability may be estimated, tests of 30 readings or more can be processed statistically for a more reliable indication of 5.1.3 Gage Geometry and Surface Texture. Roundness and surface texture are factors that shall he considered when thread gages are calibrated, particularly used gages that have dings or chips and/or show signs of excessive rust, corrosion, or abuse. Similarly, the finish on turned rather than ground gages can present significant problems. When rusting is severe, some laboratories will not attempt to calibrate them and will advise the gage user about the situation. Others will estimate the effects on uncertainty and get customer approval before proceeding. Some will calibrate the gages if possible but include a note in their report to Indicate the state of the gages and the fact that the uncertainty shown does not include the effects of their condition.
5.2 Uncertainty Factors for Pitch (Groove) Diameter CaLibration
5.2.1 Thread PLug Gages
(a) temperature
(b) uncertainty from calibration of gage blocks used as a setting master
(c) uncertainty in the calibration of thread wire size1
(d) variations in measuring force from specified values
(e) uncertainty in the calibration of the measuring instrument
U) variations in thread wire roundness/taper’
(g) cosine error
5.2.2 Setting and Checking PLug Gages for Thread Ring Gages.