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The structure and properties of thermally sprayed coatings depend directly on the state of the particles before impact on the substrate or the already deposited coating layers. Monitoring particle parameters can thus provide a unique tool for optimising coating properties as well as controlling spraying processes during coating deposition. In this paper, a new optical sensing device for on line monitoring of temperature, velocity, diameter, and trajectory of in flight particles during coating production is described. Thermal radiation emitted by in flight particles is collected by a sensing head that can be attached to the gun providing continuous monitoring of the spray process. The collected radiation is transmitted through optical fibres to a detection cabinet located away from the dusty environment around the operating spray gun. Tests were carried out on two identical plasma torches with significant differences in deposition efficiency. Measured particle flowrates were in agreement with efficiency differences.

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