Coating thickness gauges measure the thickness of paint, plating, anodizing, galvanizing, and other coatings on metal substrates. They use magnetic induction (for non-magnetic coatings on steel) or eddy current (for non-conductive coatings on non-ferrous metals) principles. Calibration verifies accuracy using certified coating thickness standards on reference substrates.
Inspect the probe tip for wear, scratches, or contamination. A worn probe produces inconsistent readings and poor repeatability. Verify the probe cable is intact and the connector is clean.
Place the probe on an uncoated reference substrate (steel for magnetic mode, aluminum for eddy current mode) and verify the reading is near zero. Record the as-found zero reading.
Using certified plastic shims of known thickness placed on the bare reference substrate, verify the gauge reading at a minimum of four thicknesses spanning the measurement range (e.g., 25 µm, 100 µm, 250 µm, 500 µm). Record the reading for each standard.
Take five consecutive readings on one certified shim, lifting and repositioning the probe each time. Calculate the standard deviation to assess repeatability.
If the gauge will be used on curved surfaces, verify accuracy on a curved reference piece with known coating thickness. Surface roughness affects readings, so note any systematic differences between smooth and rough substrates.
Record all data, standard shim certifications, substrate identification, and measurement uncertainty. Issue the calibration certificate and apply the calibration label.
Per ASTM D7091, accuracy must be within ±(1 µm + 3% of reading) for measurements up to 1000 µm, or per the manufacturer's specification if tighter. Repeatability (standard deviation of five readings) must not exceed 1% of the mean reading or 0.5 µm, whichever is larger.
12 months; daily verification with certified shims
Magnetic induction gauges measure non-magnetic coatings (paint, zinc, chrome) on ferromagnetic substrates (steel). Eddy current gauges measure non-conductive coatings (paint, anodize) on non-ferrous metal substrates (aluminum, copper, brass). Dual-mode gauges can measure on both substrate types.
For highest accuracy, yes. Substrate composition, thickness, and geometry affect gauge response. Calibrating on a flat steel reference plate and then measuring on thin-wall tubing or an alloy steel may introduce errors. Application-specific verification on actual part material is recommended.
Certified shims are precision plastic films of known thickness that simulate coatings when placed on a bare metal substrate. They provide a traceable reference without needing actual coated samples. Shims must be handled carefully to avoid stretching, wrinkling, or contamination.
CalibrationOS tracks due dates, stores certificates, and generates audit-ready reports.
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