The need for speed implies the requirement for speed sensing. Speed sensors provide the input and feedback data to monitor and control motors and other rate sensitive linear and rotary applications.
For example, the throughput of automated high-speed production lines depends on many parameters but the line speed is an early indication of expected versus unexpected output. The speed sensors can operate as part of a conveyor system, such as a conveyor belt scale that allows calculation of belt speed as well as belt loading, rate and more.
In building automation, monitoring of the fan belt speed and detecting a belt failure are desired system characteristics. An inductive sensor with integrated speed evaluation capability can provide data for the control system.
Sensing techniques for monitoring speed and measuring performance in turbines, include Hall effect, magnetoresistive, inductive and other technologies. However, any rotating shaft can be a target for speed sensing. One of the newer techniques for speed sensing is a Magnetic Logic Unit (MLU) sensor that changes resistance based on magnetic field density.
Brushless DC motors typically use Hall effect sensors to control the phases and provide electrical commutation. Hall effect sensors have many variations including omnipolar, bipolar and unipolar and both analog and digital outputs. The ability to sense zero speed is important in speed sensing applications and this is one option available for Hall effect sensors. Other circuitry that is readily integrated into the Hall effect IC includes short circuit and reverse battery protection as well as system enhancements such as dynamic offset calibration and low jitter output.
