Quality Magazine - March 2009 - (Page 42) | QUA LIT Y T EST & IN S P E C TI O N | sn, is calculated with these measurements and is included in the measuring uncertainty budget as the standard deviation, uObject (Type A). The standard uncertainty of the test equipment uPM = 198 nm and the object uObjekt = 473 nm as well as an estimated value of 500 nm for the unknown systematic measuring uncertainty are used to determine the additional measurement program related measuring uncertainty test process U for the shaft diameter 38.12 js7. The measuring uncertainty represents an interval within which the unknown “true” measurement result can be determined with the defined probability (P = 95%, k = 2). The suitability of the test process can be determined by looking at the ratio of the extended measuring uncertainty to the characteristic tolerance. With a shaft diameter of 38.12 js7, for example, and a diameter tolerance T of 24 µm, the ratio equals U:T = 0.049. Figure 4 Trace Rz = 2.3µm Probe TK100 Lt = 480mm Vt = 0.50 mm/s 4.80 Contour Peakline Source: Hommel-Etamic America Figure 5 Test Equipment Designation: Manufacturer: ID No. Resolution: Optical shaft measuring system ABC Co. Device No. 10100608 0.1 µm Accepted Measuring Variable Shaft Diameter 38.12 js7 Min. limit Value Max. limit value Tolerance 38.108 38.132 24 µm Test Object Gear Shaft Drawing no. 56-0897-xx Standard/ID number Step-Master 8-140 L211 Standard cert. no. 3D-0511-115 Measuring Conditions Measurement of the workpieces in accordance with requirement calibration of the measuring system including built-in calibrated Step-Master (standard) Automatic compensation of the measurement deviations due to deviations in the temperature of the environment and of the workpieces from the reference temperature of 20 C. Workpieces are free of contamination. Standard uncertainty u (ux ) in nm i Type/determination method Limit value a in nm Limit value a in nm Number of measurements n Standard test equipment uncertainty Unknown systematic deviation usys Inspector Add ✓ A 50 ✓ B Transfer of suitable sheet test equipment 500 Rectangle 0.58 - 198.6 290.0 39435 84100 u(x )² in nm i Source uncertainty components u(xi) Standard 1 473.9 224588 Combined standard uncertainty . U = k · u = 1180.0 nm k=2 Characteristic tolerance T = 24 Extended measuring uncertainty Request suitability of test process general preset freely selected Actual value for the ratio . Result The test process is suitable! . . Minimal testable tolerance in nm . Source: Hommel-Etamic America 42 QUALITY | March 2009 www.qualitymag.com Part of u(x )² to i u(y)² 11% 24% 65% Transformation coefficient b c weighting xi n* http://www.qualitymag.com
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