Sensor bearing for industrial machinery. Source: NSKSensor bearing for industrial machinery. Source: NSKAccurate measurement of speed, acceleration and direction parameters is critical in rotating applications like AC motors and industrial machinery.

Traditional solutions incorporate external sensors but this results in additional space requirements, heavier assemblies and extra components to purchase.

Bearing manufacturers have developed the sensor bearing as an alternative to standalone sensors. Sensor bearings are mechatronic machine components that feature a bearing and a sensor packaged together. The result is a compact solution that reduces weight, takes up less space, and cuts purchasing, manufacturing and assembly costs.

Although the names are similar, sensor bearings and bearing sensors are not the same. A sensor bearing has an integrated sensor that measures bearing speed and direction which is relayed to a control system. Bearing sensors are a standalone sensor mounted near a bearing. Although external sensors can be used to determine speed or direction, bearing sensors typically measure temperature or vibration and are primarily used for condition monitoring.

Sensor bearings were first introduced with anti-lock braking systems (ABS) in automobiles in the mid-1980s. ABS systems required measurement of the variations of the circumferential speed of the wheel. Leading bearing manufacturers at the time began development of “smart” bearings that included sensors.

As ABS systems evolved, bearing sensors were phased out of the design in favor of active wheel speed sensors to provide wheel speed data for anti-lock brakes, traction control and stability control systems.

Sensor bearing cross-section. Source: Schaeffler FAGSensor bearing cross-section. Source: Schaeffler FAG

Although they are no longer used for ABS systems, millions are in operation around the world in industrial and automotive applications such as AC servo motors, DC servo motors, hydraulic motors, electric vehicle drive systems, tractors, forklifts and conveyors. Sensor bearings today are manufactured by SKF, NTN, Schaeffler (FAG), and NSK among others.

These bearings are used for:

  • Counting the number of revolutions
  • Speed measurement
  • Direction of rotation
  • Relative position or counting
  • Acceleration or deceleration

How sensor bearings work

A magnetic pulse generator ring with alternating north and south poles is mounted to the rotating inner ring. The stationary outer ring carries the sensor housing with embedded Hall cells. As the inner ring rotates, the generator ring passes over the stationary magnetic sensor and detects the change in magnetic polarity, generating an electrical signal with a rectangular waveform. Numerical processing converts these signals into rotational speed data and direction of rotation.

Sensor bearing output. Source: SKFSensor bearing output. Source: SKF

Although sensor bearings are not practical for every application, they are ideal options for reducing equipment size and weight in applications where speed and direction measurement are important. Improvements in the latest generation of smart bearings can deliver higher performance and reliability at lower operating costs.


SKF Sensor Bearing Units

SKF Sensor Bearing Units (pdf)

NTN Integrated Rotation Sensor Bearings (pdf)

NSK Sensor Bearings for Industrial Machinery (pdf)

FAG Sensor Bearings in Electric Car Motors (pdf)