Coating thickness is considered to be one of the most important characteristics of thermally sprayed coatings. Therefore, it has long been the goal to be able to control it. This could be achieved by implementing an online, closed-loop control. A prerequisite for such a control mechanism is a feedback signal of the coating thickness with sufficiently small measurement uncertainty. Optical distance measurement techniques have been demonstrated in the past to produce promising results for such applications. This paper analyses the measurement uncertainty of an optical distance measurement technique based on confocal distance sensors used for in situ coating thickness evaluation. As an alternative, pneumatically actuated length gauges are also used for the in situ measurement. Both techniques are applied during atmospheric plasma spraying of samples in a carousel setup. The two sensing techniques are compared with a reference, destructive coating thickness measurement method. Pros and cons of using different in situ coating thickness measurement techniques for process control applications are discussed.

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