ISO 1463:2021 pdf download – Metallic and oxide coatings — Measurement of coating thickness — Microscopical method.
Repeated calibrations of the micrometer eyepiece can be reasonably expected to have a spread of less than 1 %. The distance between the two lines of a stage micrometer used for the calibration shall be known to within 0,2 µm or 0,1 %, whichever is the greater. Some image splitting micrometer eyepieces have a nonlinearity that introduces an uncertainty of up to 1 % for short measurement distances. Uncertainties can be introduced by backlash in the movement of the micrometer eyepiece. To avoid this uncertainty, ensure that the final motion during alignment of the hairline is always made in the same direction. 5.10.2 Digital image processing Microscopes with a triocular tube, camera adapters with projecting lens and digital cameras connected to a computer with software for image capturing and processing are nowadays state of the art. Similar to 5.10.1, the measurement will be no more accurate than the adjustment and calibration of the length measurement function (combination of hardware and software). For adjustment, digital images from the stage micrometer (in both directions parallel to the x- and y-axis of the image) are recorded for every combination of objective, if applicable intermediate magnification changer, and resolution setting of the camera (full resolution and typical settings of pixel binning). The length in object space represented by a pixel of the digital image is calculated by measuring a known distance on the stage micrometer with the respective function of the software and is then saved in the software. Usually after such an adjustment, the images are recorded “calibrated ”, i.e. with the µm/pixel factor assigned to the image, by selecting the objective, if applicable the intermediate magnification changer, and the pixel setting of the camera in the software at the time of capturing the image. The adjustment and/or calibration are usually stable for long time. Furthermore, they are not operator dependent as long as no changes are applied to the tube, if applicable an intermediate magnification changer, the camera adapter or the camera itself, and as long as the same resolution of the camera (number of pixels in x and y direction) is used for adjustment and/or calibration and for measurement. Normally, it is sufficient to record in regular time intervals images from the stage micrometer and measure known distances. When the deviation between the measured length and the certified length is less than a reasonably defined uncertainty limit for length measurements, which the laboratory wants to achieve, e.g. 1 %, the calibration is still valid and no re-adjustment is necessary. 5.11 Uniformity of magnification Uncertainties can occur if the magnification is not uniform over the entire field of view. Thus, ensure that both the calibration and the measurement are made over the same portion of the field of view with the measured boundaries centred about the optical axis. 5.12 Lens quality As lack of sharpness of the image contributes to the uncertainty of the measurement, ensure that good quality lenses are used. NOTE Sometimes, image sharpness can be improved by using monochromatic light. 5.13 Orientation of measuring lines Ensure that the movement of the hairline of the eyepiece for alignment or the measuring line of a digital image processing software is perpendicular to the boundaries of the coating cross-section, e.g. 10° misalignment will contribute a 1,5 % uncertainty.
ISO 1463:2021 pdf download – Metallic and oxide coatings — Measurement of coating thickness — Microscopical method
