Speed Sensing (the Hall Effect) John Hoyt

Need for Speed Sensors ► Team Hybrid may use a drive-train system that uses drive shafts driven by separate components. If this is the case, the ability to monitor the rotational shaft speeds and adjust power accordingly will help the overall system perform effectively.

Background ► Dr. Edwin Hall discovered the Hall effect, which bears his name, in ► If a conductive material is placed in a magnetic field (with the field oriented perpendicular to the material) and a current is passed through the length of the material, a voltage drop will be produced across the width of the material.

The Hall Effect ► V = IB/(ned)  V is the Hall voltage across the material  I is the current  B is the magnetic flux density  n is the “bulk density of the carrier electrons”  e is the electron charge  d is the material thickness

Speed Sensing ► Fit a magnet (or two) to a rotating shaft ► Mount a Hall Effect sensor near the shaft (explained later) ► As the magnet nears the sensor, the Hall voltage will rise, until it spikes as the magnet passes by

Hall Effect Sensors ► Produce an output voltage which is very small, and must be amplified in order to be used ► Two types of outputs  Analog  Digital

Analog Output

Digital Output

Advantages ► Does not require physical contact to work which eliminates possible wear ► Not affected by outside elements such as dirt, dust, water, or any combination of these

Applications ► Motion sensing ► Power sensing ► Position sensing  Ignition and fuel injection systems ► Speed sensing  ABS systems

Resources ► autopartscorner.com ► electronicproducts.com ► honeywell.com ► howstuffworks.com ► hyperphysics.phy-astr.gsu.edu ► sensorsmag.com ► wikipedia.com ► “The Hall Effect” by Jacob Wernhoff

Questions