Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 441 of 707

Illustration of three probes with the measuring areas detailed. Probe frequency determines measurement range. diameters are sized to accommodate the size and shape of the parts being mea- sured. Probes with smaller tips can measure on very small areas of parts less than 90 mils. Smaller probe tips are subject to increased wear and are more easily worn or damaged, so probes are also produced with larger diameter tips for measuring on larger parts such as plated brackets or castings. Depth of measurement penetration is a function of the conductivity of the coat- ing and substrate as well as the frequency of the probe being used. The specific frequency for the probe is chosen depending on the application plus the coating thickness specification. Lower frequency probes penetrate deeper into the parts than higher frequencies. The higher the probe frequency, the better the accuracy will be for measuring thinner coatings. Right angle probes are also available that can be used to determine thickness inside bores as small as .250" diameter. Placing and holding the probe steady at the proper angle inside a bored hole is very difficult, increasing likelihood of measurement error due to improper probe positioning. To obtain the maximum accuracy achievable, a probe stand should be used for measuring inside internal bores or on small part surfaces. With PSEC the same probe can often be used for measuring different applica- tions. For example, conductive coatings on steel and non-conductive coatings on conductive substrates can be measured using the same probe. SUMMARY Phase-sensitive eddy current technology provides an excellent option to metal fin- 440 Picture of probe stand being used to measure small parts. Picture courtesy of UPA technology

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