Quality Assurance & GD&T // Protocol ISO-03

Metrology Tolerance & ISO 10360-8 Checker

Evaluate optical scanner volumetric error limits (MPE_E = ±(A + L/K) µm), test uncertainty ratios (TUR), and ISO 14253-1 conformance against engineering drawings.

Scanner Metrology Verification Class

Measured Feature Length (L in mm)300 mm

Drawing Bilateral Tolerance (± mm)

Drawing limit: ±0.100 mm

Measured CAD Deviation (mm)

Actual surface delta: +0.035 mm

ISO Conformance Verdict

Conforming (Pass)

Measured deviation is safely inside the acceptance zone after subtracting measurement uncertainty.

MPE_E Volumetric Limit

±21.5 µm

±0.021 mm

TUR (Gauge Capability)

6.6 : 1

Meets 4:1 rule

Expanded Uncertainty U95%:±15.0 µm (±0.015 mm)

Guard-band Safe Zone:±0.085 mm

Probing Form Error Pf:14 µm

Metrology Conformance Protocols

ISO 10360-8 Volumetric Accuracy & Guard-Banding

1. Volumetric Length Error Equation (MPE_E)

Optical CMMs and structured light sensors specify length measurement accuracy using the linear degradation model:

MPE_E = ±(A + L / K) µm

Where $A$ is the intrinsic noise floor of the optics and camera detector (in µm), and $L/K$ represents the scale-dependent error caused by temperature drifts, thermal expansion mismatches, and photogrammetric bundle adjustment deviations over distance $L$.

2. ISO 14253-1 Decision Rules

Under international metrology standards, a measurement cannot be declared in conformance merely because the nominal reading falls inside the drawing boundary:

Conformance Zone: Drawing tolerance reduced by the expanded uncertainty U_95%. Only parts within this restricted envelope guarantee 95% confidence.
Guard-Banding: When readings fall within the uncertainty zone, neither customer nor supplier can prove pass/fail without incurring legal liability or secondary CMM touch probing.