The expenses related to the rejection and replacement of imperfect coatings can reach 15% of the production cost. Thus, for manufacturers, the reproducibility and reliability of plasma sprayed coatings are the main goals for respecting quality standards and decreasing production cost. The aim of this paper is a tentative to answer to the questions: —Which diagnostics can be used within harsh conditions prevailing in spray-booths? —Which close-loop control can be achieved between the on-line measured parameters and the spraying process macroscopic parameters?