Tooke Film Thickness Standards

Operating instructions for measuring instruments will normally include calibration procedures. In the absence of written procedures, the user is advised to contact the instrument manufacturer. In general, proximity type instruments are most reliably calibrated for a given measurement by selecting two standard films which “bracket” (one above, one below) the expected film thickness to be measured. By first causing the instrument to read both standards correctly over a bare surface (the same or similar to the coated one), then the unknown reading should be correctly made. Of course, the narrower the range between the two standards the lesser are the possibilities of errors due to instrumental non-linearities.

An optical-mechanical gauge may be calibrated by the owner following a simple verification procedure on a standard test panel. If observed thicknesses deviate from “true” values, a calibration curve can be drawn to specify necessary corrections. Restoration of “zero” correction, if desired, will usually require attention by the manufacturer’s shop to re-establish precise alignment.