Calibration, verification, adjustment, spot layout, coupling, records — a reliable measurement is built from a set of disciplined actions. This section gives step-by-step procedures and self-check lists you can apply on site.
ASTM D7091-22 breaks gauge use into three steps: Calibration (done once by the manufacturer or a lab), Verification (performed by the operator every shift), and Adjustment (done on site when…
The base metal reading (BMR) is the “false thickness” measured on bare substrate, coming from surface roughness, substrate material and geometric curvature; both SSPC-PA 2 and ISO 19840 require measuring…
SSPC-PA 2-2022 uses a two-level sampling plan: spot measurement (the average of no fewer than 3 readings within a roughly 1.5-inch diameter circle) and zone statistics (number of spots set…
Shim verification is the every-shift action required by ASTM D7091-22: place a shim of known thickness on bare substrate, and the reading versus nominal must fall within tolerance; common mistakes…
Errors on curved, small and edge surfaces come from incomplete contact geometry: convex reads high, concave reads low, edges read unstable; countermeasures include a small-diameter probe, calibration on a same-curvature…
Rough surfaces (blast-cleaned steel, hot-dip galvanising, concrete) make readings read systematically high; the correction is to first measure the base metal reading on uncoated substrate of the same roughness and…
Ambient temperature affects the gauge electronics and the coating state, humidity affects surface coupling and the sound speed in substrates like concrete, and the coating cure state directly decides whether…
Ultrasonic thickness readings depend heavily on coupling: pick the couplant for the job, use the right amount, spread it evenly; keep the probe perpendicular, pressure steady, no sliding; when the…
An auditable thickness acceptance report should contain: project and zone identification, gauge model and serial number, calibration status and certificate number, method and environmental conditions, spot positions and point-by-point readings,…
Most errors in coating and wall-thickness measurement come from procedure, not the instrument: wrong principle for the substrate, no zero adjustment, measuring uncured coating, missing shim verification, poor handling of…
