Skip to main content

How Hall Effect Sensors Work

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

Comments

  1. 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

Post a Comment

Popular posts from this blog

Selecting the Correct Gauge Wires for your RC Models

When we are building RC models (aircrafts, multicopters etc.), something we typically overlook is what type of wires to use to distribute power in them. Usually, we try to reduce the weight of the model, so we tend to go with smaller wires. But, we cant expect to put in small circuit-wires and have them handle the amount of power needed. If you look at the wires that comes in the output leads of a Li-Po, or the wires that comes on a standard XT Jack, you'll notice that they're quite huge. Large gauge wires on a Li-Po and XT connectors These need to be huge to handle the amount of amperage that goes through them. So, we should also consider the amperage, and the length of wire needed when selecting the size (gauge) of the wires.

What do the prop size numbers mean?

Have you been trying to shop for propellers - either online or at a hobby shop - and got confused of the numbering used to denote the size of the propellers? You see things like " 10 x 4.5 CW ", or " 8055 CCW ". What do these numbers mean? A 8 x 4.5 CW and CCW Propeller Set It's actually quite simple once you figure it out. The first number denotes the diameter of the prop (length from tip-to-tip). The second number denotes the pitch of the prop. Here, the pitch is denoted as a length, not a angle. Let's see how that works.

Li-Po Batteries Explained - Part 2

I explained about Li-ion batteries (the predecessor of Li-Po) in my earlier post ( Li-Po Batteries Explained - Part 1 ). Now let's see what these 'Lithium Polymers' are. Lithium-Polymer Batteries - The real ones Li-Po batteries - also known as Li-Poly, Pi-Pol, PLI and PLI - are a type of rechargeable batteries that uses same types of electrodes as the Li-ion batteries. The difference is with the electrolyte it uses. Instead of the liquid solvent used in Li-ions, Li-Po uses a polymer electrolyte. In the original design, which dates back to the 1970's, the electrolyte is a dry, plastic-like, thin film. It doesn't conduct electricity, but allows the exchange of ions between the electrodes. Theoretically, with this design, batteries could be made very thin (less than 1 millimeter) and to a variety of form factors. And because of the electrolyte being dry, the manufacturing process can be simplified and the safety of the battery will be higher because of no risk in