Measurement Uncertainty: length_cmm
GUM-compliant measurement uncertainty budget components and coverage factors for common engineering measurements. Covers Type A (statistical) and Type B (non-statistical) uncertainty sources with standard uncertainties, expanded uncertainties at k=2 (95%), and confidence levels for: length/dimension (caliper, micrometer, CMM, gauge block), mass (analytical balance, platform scale), temperature (Type K thermocouple, Pt100 RTD, IR pyrometer), pressure (Bourdon gauge, electronic transducer, liquid manometer), flow (orifice plate, turbine meter, Coriolis, ultrasonic transit-time), electrical (DMM, power analyzer), force (load cell), and torque (torque wrench). Also includes coverage factor reference rows (k=1/2/3, 68/95/99.7%) and distribution divisors (rectangular, triangular, normal, U-shaped). Per ISO/IEC Guide 98-3:2008 (GUM), NIST TN 1297, ISO/IEC 17025:2017.
| measurement type | uncertainty source | confidence level pct (%) | coverage factor k | distribution | divisor | expanded uncertainty k2 | expanded uncertainty unit | notes | standard uncertainty unit | standard uncertainty value | uncertainty type |
|---|---|---|---|---|---|---|---|---|---|---|---|
| length_cmm | combined_standard_uncertainty | 95 | 2 | normal | 1 | 0.008 | mm | RSS: sqrt(0.002^2+0.003^2+0.001^2+0.002^2) approx 0.004 mm; U95=0.008 mm; consistent with good CMM performance | mm | 0.004 | Combined |
| length_cmm | probe_qualification | 95 | 2 | normal | 2 | 0.004 | mm | CMM probe qualification (reference sphere calibration) contributes uncertainty from reference sphere certificate; typical 0.002 mm | mm | 0.002 | Type_B |
| length_cmm | repeatability | 95 | 2 | normal | 1 | 0.002 | mm | CMM repeatability: standard deviation of probe lobing test; typically 0.001-0.002 mm for bridge CMM; lower than handheld instruments | mm | 0.001 | Type_A |
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