Measurement Uncertainty: flow_ultrasonic_transit_time
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 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| flow_ultrasonic_transit_time | calibration | 95 | 2 | normal | 2 | 0.6 | pct_flow | Clamp-on ultrasonic: calibration uncertainty dominated by path length and transducer positioning; insertion type better U95 = 0.5-1.0% | pct_flow | 0.3 | Type_B |
| flow_ultrasonic_transit_time | combined_standard_uncertainty | 95 | 2 | normal | 1 | 1.16 | pct_flow | RSS: sqrt(0.3^2+0.5^2) = 0.583% flow; U95 = 1.2% flow; clamp-on suitable for check metering not fiscal | pct_flow | 0.58 | Combined |
| flow_ultrasonic_transit_time | installation_profile | 95 | 2 | normal | 2 | 1 | pct_flow | Velocity profile distortion from upstream elbows or valves; 20D upstream straight run reduces to 0.5%; less straight run increases error | pct_flow | 0.5 | Type_B |
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