Sensors are used in a multitude of devices and equipment to detect the presence of objects or other phenomena. These components are used in applications ranging from automation, computer sensors, cars, and many other products that are a part of our everyday lives. In this blog, we will discuss the Hall effect sensor, which is one type of sensor that finds use in countless applications.
The Hall effect refers to the phenomenon that occurs when a voltage differential is created across a conductive material in the presence of a magnetic field that is perpendicular to the current. The eponymous effect is named after physicist Edwin Hall, who observed that this configuration moved electrical charges in the same direction and created an opposite charge at either pole. Different materials generally tend to have varying affinities towards pulling the charge in either direction. For example, most metals have a negative predominant charge, whereas the opposite is true for a minority of conductors like zinc, beryllium, and cadmium.
Hall effect sensors, therefore, can detect the strength and presence of a magnetic field around a material. These devices apply a current to a thin piece of metal and then sense the voltage difference that would occur when the conductor is near a magnetic field. Because the voltage is directly proportional to the magnitude of the magnetic field, a higher voltage difference would imply a stronger magnetic field. Unlike an inductive sensor, which only recognizes dynamic changes in magnetic fields, Hall effect sensors are best suited for static fields.
There are generally two types of Hall effect sensors used in most applications, linear and digital. Linear or analog sensors apply a continuous current which varies depending on the strength of the surrounding magnetic field. Conversely, digital sensors use a Schmitt trigger to deliver current, which increases or decreases in a stepwise manner when the voltage reaches a certain threshold. Digital Hall effect sensors can be further subdivided into bipolar and unipolar variations. Unipolar sensors can only be activated and deactivated by a positive field created by a magnet with a south polarity. On the other hand, bipolar sensors are triggered by a positive, south-facing magnetic pole and require a negative north-facing pole to be released.
Choosing a Hall effect sensor for a particular application is usually dependent on the detection mechanism of the device, being either head-on or sideways. Head-on detection requires the field to approach the sensor in a linear and direct manner. As such, the output voltage drastically increases as the magnet gets closer to the sensor, making these devices indispensable in measuring the proximity and position of the object they are attached to. On the other hand, sideways detection devices are activated when the field is angled towards the sensor at a right angle. With this configuration, it is possible to sense rotational movement, making this type of sensor popular in detecting how fast a motor is moving.
Since magnetic fields can be measured by sampling current strength with a Hall effect sensor, the inverse is also true. This method of current sampling is more accurate than other methods and can be accomplished without direct contact, removing the risk of electrocution. Additionally, Hall effect sensors have a higher tolerance to transient overcurrents, which would otherwise damage similar devices.
There are numerous applications for both linear and digital Hall effect sensors. Some of the most popular are thus listed:
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