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Use and Care of Gauging Sheet (Shim) Standards

These standards are plastic foils used to facilitate calibration of eddy current and magnetic induction instruments for the measurement of non-c0ndcutuive coatings (e.g., paint, anodize) on non-magnetic substrates (e.g., Al, Cu, brass) and/or non-magnetic coatings (e.g., paint, zinc plating) on ferromagnetic substrates (e.g, steel, Kovar). These plastic foils are placed onto a blank substrate with the instrument probe on top of the foil pressed against the substrate to do the calibration. As some of the gauging sheet products we provide are relatively thin and the measurement involves contact between the probe and the plastic shim, there are certain precautions and practices we recommend to preserve the integrity of your gauging sheet standards and extend their useful life:

1. Always keep the shims clean. You may use a soft cloth wetted with alcohol to gently wipe any dirt or other foreign substances from the surface of the standards. Any foreign substances on the shim standards may cause erroneous measurements.

2. Make sure the blank base metal you plan to use with the shim standards is clean and free from any sharp edges or burrs which may tear the thinner shim standards.

3. It is preferred to calibrate on flat surfaces. But there are cases where it is necessary to wrap shims around curved or complex shaped surfaces to produce a valid calibration. In such cases it is advisable to use probe stands offered by the suppliers and to proceed carefully when wrapping shim standards onto curved or complexly shaped surfaces.

4. Always move the probe in an up and down fashion when contacting the shim standard. Do so by moving the probe slowly and carefully onto the surface of the shim standard, allowing the natural force exerted by the probe’s spring to be the only force in effect when making contact with the shim standard. Try to never allow the probe to slip or slide on the surface while it is in contact with the shim.

5. Always store shim standards in the plastic box provided for this purpose. Make sure the shim standard is lying flat against the soft foam material in the box so that closure of the box does not fold or crease the shim.

6. Any shim standards, especially thin shims , 1 mil (25 microns) thick of less, with considerable wrinkling and creases should be replaced as errors in calibration can arise from shims with highly wrinkled surfaces.

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