Air gap measurement in large electric motors


With all electric motors, a smooth operation is required in order to ensure a long operating life. Particularly with large motors, imbalance can cause significant damage in the running motor, resulting in high financial losses. Capacitive sensors from Micro-Epsilon reliably monitor the concentricity during running.

Large electric motors are intended for use in rock grinding mills for cement production or mining. Sensors monitor if the rotor, which is the moveable part inside the electric motor, is running smoothly in combination with the stator, which is the stationary part. Due to imbalances inside during operation, the rotor can come into contact with the stator, which would cause much damage to the motor.

Capacitive sensors from Micro-Epsilon designed for non-contact displacement and distance measurements reliably monitor the operation. Therefore, the sensors are used to measure the distance between the stator and rotor and to monitor the so-called rotor gap. For this measurement task, capacitive sensors with a measuring range of approx. 30mm are used.

Inside an electric motor are some challenges to be mastered. The capacitive capaNCDT 6220 sensor enables 100 per cent reliable inspection. The capacitive sensors are resistant to the magnetic fields that occur regularly inside the electric motor. Due to the restricted installation space, flat capacitive sensors with a height of just 2.5mm are used. The cable length is another important aspect. Due to the enormous size of the motor, cable lengths of 8m or longer are necessary. In total, one motor normally has 8 sensor channels, but up to 16 channels can also be installed. Permanent retooling is not necessary. Measurements are generally carried out in a non-contact manner, ensuring long-term reliability and stability.

Accuracy, stability, resolution and measuring rates are the most important characteristics of capacitive sensors. They monitor movements, tolerances of parts and are responsible for process control. The parameters to be measured are very diverse: oscillation, amplitude, clearance, position, tilt angle, planarity, profile, deformation, gap, stroke, roundness, thickness, displacement, contour, etc.

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