Measurements of relative vibrations in electric motors

The article presents the problem of diagnostics of electric motors on slide bearings using measurements of relative vibrations. This motor diagnostics method is not applied in Poland. It is used for diagnostics of turbine sets. It is worth using the method of relative vibration measurement to diagnostics of motors using slide bearings. Vibrations are measured by two proximity eddy-current sensors measuring displacement of vibrations, located in a bearing casing or near the casing on a plane perpendicular to the rotor axis. There is an angle of 90° is between the sensors and 45° between sensor axes and the horizontal plane. A voltage signal of a single sensor depends on the distance between the sensor and the surface of the shaft in a given moment of time. XY type oscilloscopic observation of signals coming from a two-sensor system enables to observe the trajectory of the movement of the pivot middle. The diagnostics of motors uses characteristic diagnostic relations between inefficiencies of a turbomachine on slide bearings and features of the trajectory of the pivot movement in respect of the bearing sleeve. The following are accepted as features of the trajectory: size of trajectory; turn of rotation direction of a point in the trajectory; period; shape; invariability of trajectory features in time