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How Hall Effect Sensors Work

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If you have studied about brushless motors, you'll probably know that they need a electronic controller (ESC) to run. Since the ESC can't actually see how the motor is running,  it needs to somehow detect the orientation of the rotor (moving part) relative to the stator (stationary part) of the motor. The two most popular ways of doing this is to use a Hall Effect Sensor or to measure the Back EMF of the undriven coils.

The Back EMF method does not require any additional sensors, but it's implementation is complicated and has to overcome several issues. The Hall Effect method is much simpler than that, but requires a Hall Effect Sensor near the rotor of the motor to operate.

So, how does a Hall Effect sensor work?
Simply put, it is a device that varies its output voltage based on changes on a magnetic field.

The operation of the sensor is based on the Hall Effect which was discovered by Edwin Hall in 1879. The theory is explained as follows, 
The Hall Effect



When a electrical current is flowing through a conductor which is placed in a magnetic field perpendicular to the current, the magnetic field produce a force on the flowing electrons which tends to push them towards the sides of the conductor. This produces a voltage difference between the sides of the conductor which is known as the Hall Voltage.

If the magnetic field is known (such as in a fixed magnet), the hall voltage can be measured to determine the distance from the hall plate (the conductor). If array of sensors are used, the relative position of the magnet can also be determined.

A hall effect sensor as a rotation detector
As discussed above, Hall Effect sensors are commonly used in brushless motors to detect the position of the rotor. The same concept is also used in disc drive speed regulators and also in engines for ignition timing and anti-lock braking systems. Computer printers use them to detect missing paper and open covers. Industrial applications include detecting the position of pneumatic cylinders.

Since a conductor carrying electricity also generates a magnetic field that varies according to the current, a Hall Effect sensor can be used to measure the current without interrupting the circuit.

References 
http://en.wikipedia.org/wiki/Hall_effect_sensor
http://en.wikipedia.org/wiki/Hall_effect
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/hall.html
http://en.wikipedia.org/wiki/Brushless_DC_electric_motor
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Comments

  1. acdOctober 13, 2012 at 12:16 AM

    Hall effect Current Sensor gives isolated DC voltage out put proportional to the AC or DC Current passing through. Sensors with higher Current ratings are in the offing.Systems new Current Sensor uses Hall effect to sense AC or DC Current. The sensor is totally isolated from main Current and not susceptible to external disturbances.

    Current Sensor

    ReplyDelete

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