Homework #1: Automobile Sensors

Chris BuckinghamECE-85256/9/2015

Hall effect sensors are used extensively in the automotive market. From speed sensing and ignition control to powered seat and window controls, variations of the Hall effect sensor have found a comfortable home in most modern automobiles.

The Hall effect (or Hall voltage) is mediated fundamentally by the Lorentz force. The Lorentz force is brought about when a charged particle moves with some velocity in the presence of an electrical field through a magnetic field [1]. The force is heuristically imagined using the right and rule (shown below along with the application with the rail-gun)

Figure 1: right hand rule and rail gun operation

For this discussion the application in RPM sensing will be investigated.

Figure 2: typical configuration in RPM sensing for

As the teeth (or tape/window) passes over the air gap between the sensor housing and rotating component (trigger wheel) an alternating positive/ negative voltage is output by the Hall effect device. The rate at which the signal repeats is correlated to the speed of the specific rotor. These sensors have the advantage of being relatively immune to harsh environmental conditions e.g. contamination, heat, pressure, etc. they also cost less than a mechanical sensor with greater accuracy and relibility.