A Bourdon-tube pressure gauge is calibrated on a dead-weight tester
PHYSICS · Multi-part · Fermi University Physics · Scientific Practice & Experimental Methods · Quantities, units and the practice of measurement · Uncertainty in measurement
Measurement and Method, Ch The instrument: resolution, sensitivity, calibration and traceability
Problem
A Bourdon-tube pressure gauge is calibrated on a dead-weight tester, whose applied pressures are traceable and treated as exact. Vented to atmosphere (reference pressure p1=0.0kPa) the gauge indicates I1=1.4kPa. Loaded to a reference pressure p2=1000.0kPa the gauge indicates I2=1013.6kPa. Repeating a reading shows the gauge's repeatability is ±0.3kPa, and this applies to every reading it gives, including the two calibration readings above. The gauge is then connected to a process line and indicates 640.0kPa.
((a)) Fit the straight line True =a+b× Indicated through the two calibration points, and find the corrected pressure corresponding to the indicated 640.0kPa.
((b)) Suppose both calibration readings had been biased together, in the same direction, by the full ±0.3kPa repeatability (the worst case, since raising either one lowers the corrected pressure), and recompute the correction to see how much it would shift. Add the process reading's own ±0.3kPa repeatability directly to this shift (no quadrature) to obtain a bound on the corrected pressure.