Speed Sensing (the Hall Effect)

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Speed Sensing(the Hall Effect)

• John Hoyt

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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.

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Background

• Dr. Edwin Hall discovered the Hall effect, which
  bears his name, in 1879.
• 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.

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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

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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

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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

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Analog Output
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Digital Output
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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

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Applications

• Motion sensing
• Power sensing
• Position sensing
• Ignition and fuel injection systems
• Speed sensing
• ABS systems

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Resources

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

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Questions