ASME B89.1.13 pdf download

ASME B89.1.13 pdf download.MICROMETERS.
ASME B89.1.13 is intended to provide the essential requirements for micrometers as a basis for mutual understanding between manufacturers and consumers. Outside. inside, and depth micrometers arc described in the Standard.
2 DEFINITIONS
backlash: a relative movement between interacting mechanical parts. resulting from looseness IASME B5.54M-1992 (Rl998)I. In this Standard, backlash is further delined as the rotation of the spindle, in the opposite direction of the initial reading. before spindle moves iii a linear direction. This condition is typically caused by looseness of lit between the lead screw and adjusting nut.
bias: systematic error of the indicahon of a measuring instrument (VIM).
end s/sake: the amount of spindle movement, when an axial force is applied in the direction of the spindle alternating towards the anvil and away from the anvil. without rotating the spindle.
error (of indication) of a measursng insInnaent: indication of a measuring instrument minus a true value of the corresponding quantity (VIM).
NOTE: This conccpm applies mainly whcrc thc instrument is compared to a reiernce standard,
flatness: the condition of a surface having all elements in one plane (ASME Yl4.5M-l994.
ma.imurn permissible error (MPE): extreme values of an error permitted by specifications. etc.. for a given measuring instrument V I M).
parallelism: the condition of a surface or center plane. equidistant at all points from a datum plane or axis. equidistant along its length from one or more datum planes or a datum axis IASME Yl4.5M-l994).
D5 SOURCES OF ERROR IN INSTRUMENT CALIBRATION
Common sources of error in mechanical calibrations include the uncertainty in the master, the repeatability, resolution, parallax errors, uncertainty in the temperature of the master, uncertainty in the temperature of the test item, uncertainty in the coefficient of thermal expansion. elastic deformation, cosine errors, Abbe offset, and others, depending on the type of instrument or niaterial standards being measured, Not all of these sources contribute to the measurement uncertainty when calibrating a micrometer.
D6 SAMPLE UNCERTAINTY BUDGETS
Two sample uncertainty budgets are included, the first in metric units and the second in inch units. The dominant uncertainty source is different in the two examples.
An uncertainty budget for the measurement of the error of indication for a 0—25 mm metric micrometer is given in Table Dl. The micrometer error of indication was measured using gage blocks in a temperature- controlled room maintained at 20C i2’C. The difference between the temperature of the micrometer and the gage blocks used in the calibration was estimated not to exceed lC.
D6.1 0—25 mm Vernier Micrometer
D6.1.1 Master Values. The calibrated values of the gage blocks used in the calibration were not known. It was only known that the blocks were within the tolerances for a grade 2 set. The blocks could deviate anywhere from 0 to ±0.14 urn from nominal, so a rectangular distribution is assumed.
D6.1.2 Repeatability. The repeatability of the instrument was determined by measuring a 0.75 in. gage block .30 times. The one standard deviation was 0.45
urn The standard deviation of the mean was 0.451%30. or 0.08 lam. In all subsequent measurements only one reading will bc taken: therefore, the one standard deviation (0.45 ELm) is used in the uncertainty budget. Once the measurement uncertainty for a process has been obtained, it can then be used for all measurements made under similar conditions.
D6.1.3 Uncertainty in Coefficient of Thermal Expansion. Because the coefficient of thermal expansion is not known any better than l0. a component in the uncertainty budget is added for this effect. The coeflicient of thermal expansion of steel was assumed to be 11.5 X 10”t°C. The difference in the coefficient of thermal expansion between the two materials could be as large as 1.6 X l0PC. The standard temperature for dimensional measurements is 20°C. The uncertainty in correcting the two gages to 20°C due to the uncertainty in knowing the coefficient of thennal expansion can be expressed by the equation.