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This article presents a contactless measurement technique of the rotor temperature of small rotating machines using Near-Infrared Fiber Bragg Gratings (FBGs) sensors. This principle allows localizing heat spots in the rotor of electrical machines. The temperature information can be used to protect the machine by stopping its operation due to a heat spot. The concept is to measure the wavelength shift due to temperature changes for several FBGs integrated into a rotor. First, the temperature response of the FBG is simulated using Matlab. Then, a test bench is designed including a geometrically small electrical motor, a mechanical coupler, two bearings and a 3D printed cylinder. It has a rotational speed equivalent to a real electrical machine. The measurement principle uses a super-luminescent diode (815-855 nm) which is continuously coupled into an FBG embedded onto the rotor using suitable optics. The heating system is calibrated using a T-type thermocouple (class A: +/- 1 °C). Then, the Fiber Bragg Grating is heated while rotating the cylinder. The reflected signals are detected by a spectrometer. Finally, wavelength shifts due to temperature variations (10°C steps from 20 °C up to 70 °C) are experimentally measured up to 754 RPM. A temperature sensibility of 4.7 pm/°C is experimentally reached. As future work, the system with several gratings will be integrated into a small power rotating machine (kW) suitable for automotive applications. Reflected signals that correspond to temperature variations will be detected while rotating the FBGs to measure high temperatures ~ 150 °C for 1500 RPM.
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