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Basic Understanding of Hall effect sensor

Updated: Mar 29

What is a hall effect sensor?


A hall effect sensor is a type of magnetic sensor used to detect the direction and strength of a magnetic field that is produced from a permanent magnet or an electromagnet, with its output varying in proportion to the strength of the magnetic field that is being detected. A magnetic sensor converts magnetic signals into electrical signals for processing by electronic circuits.

Hall Effect Sensor Module
Hall Effect Sensor Module

A magnetic sensor is a solid-state device. It is becoming popular as it can be used in several different types of applications, such as sensing position, velocity, or directional movement. It is the best choice of sensor for electronics designers for the following reasons, such as:

  • non-contact, wear-free operation

  • low maintenance

  • robust design

  • sealed hall effect devices that are immune to vibration, dust, and water


One of the most significant and primary uses of magnetic sensors is in automotive systems for sensing position, speed, and distance.

For example,

  • position of car seats and seat belts for air bag control

  • angular position of crank shaft for firing angle of spark plugs

  • detection of wheel speed for the anti-lock braking system (ABS)


Magnetic sensors are designed to respond to a large range of positive and negative magnetic fields in several different applications.


A hall effect sensor is a type of magnetic sensor whose output signal is a function of the magnetic flux density around it. Hall effect sensors are devices that detect an external magnetic field. Two critical characteristics they respond to are the magnetic flux density (B) and the polarity, which includes the north and south poles. The hall effect sensor detects the magnetic flux density around it and produces a hall voltage (VH) when the flux density surpasses a specific threshold.





The Hall Effect Sensor: A Key Player in Modern Technology


The Hall Effect sensor stands at the forefront of modern sensor technology, embodying innovation in magnetic field detection. Employing the principles of the Hall Effect, this sensor excels in various applications where precise measurement of magnetic fields is paramount. Its significance in sensor technology lies in its ability to operate contactlessly, showcasing a technological marvel that minimizes wear and tear. The Hall Effect sensor's integration into sensor technology brings forth a transformative approach to position sensing, current monitoring, and speed detection. Its compact design and low power consumption underscore its prowess in the ever-evolving landscape of sensor technology, solidifying its role as a key player in advancing electronic and electromechanical systems.


Construction and Principles of Hall Effect Sensors


A hall effect sensor is comprised mainly of thin-piece rectangular p-type semiconductors like gallium arsenide (GaAs), indium antimonide (InSb), or indium arsenide (InAs), which plan an uninterrupted current flow through themselves. When the device is positioned within a magnetic field, the magnetic flux lines will apply a force on the semiconductor material. This force leads to the deflection of the charge carriers, namely electrons and holes to each side of the semiconductor slab. This charge carrier movement is a result of the magnetic field they experienced while passing through semiconductor material.


The potential difference is developed between the two sides of semiconductor material when these electrons and holes move sideways, building up these charge carriers. The movement of electrons through semiconductor material is affected by the available external magnetic field, which is at right angles to it. This effect is larger in a rectangular material that is flat in shape. By using a magnetic field, the effect of producing a measurable voltage is called the hall effect. For generating a potential difference across the device, the magnetic flux lines must be at right angles to current flow and be of the right polarity (usually a south pole).



Working of Hall Effect Sensor
Working of Hall Effect Sensor

The Hall effect delivers information regarding magnetic pole type and magnetic field magnitude. For example, the south pole will cause the device to generate an output voltage, while the north pole will have no effect. When there is no magnetic field, hall effect sensors and switches are designed in such a way to be in an OFF state (i.e., open circuit conditions). Hall effect sensors and switches will be turned on (closed circuit condition) only when they are subjected to sufficient strength and polarity of a magnetic field.


Enhancing Hall Effect Sensors with Integrated Circuits





The output voltage, named the hall voltage (VH), of the fundamental hall element is directly proportional to the strength of the magnetic field that is passed through the semiconductor material. Output voltage can potentially be very low, sometimes just a few micro volts, even when exposed to a powerful magnetic field. This is why most commercially produced Hall effect devices come equipped with integrated DC amplifiers, logic switching circuits, and voltage regulators to improve the sensors sensitivity, hysteresis, and output voltage. And hence, this allows hall effect sensors to be operated over a large range of power supplies and magnetic field conditions.



Hall Effect Sensor of Fan cooler
Hall Effect Sensor of Fan cooler


Output Types and Drive Capabilities of Hall effect sensor


They are available with linear or digital output. The linear (analogue) sensors will output a signal directly from the operational amplifier, where the voltage corresponds proportionally to the magnetic field detected by the Hall effect sensor.


This specific output hall voltage is given as:


VH = RH(I/t)B


where VH = Hall voltage in volts

RH = hall effect coefficient

I = current flow through the hall effect sensor in amps

t = thickness of the hall effect sensor in mm

B = magnetic flux density in Tesla


Linear or analog sensors give a continuous output voltage that increases with a strong magnetic field and decreases with a weak magnetic field. In linear output hall effect sensors, there are two basic types of digital hall effect sensors: bipolar and unipolar. Bipolar sensors function when exposed to a positive magnetic field, such as the south pole, for activation, and a negative magnetic field, like the north pole, for deactivation. A unipolar sensor requires only a single magnetic south pole to both operate and release it when it moves in and out of a magnetic field.





As the output drive capabilities of hall effect devices are very small, around 10–20 mm, they cannot directly switch large electrical loads. For such large current loads, an open collector (current sinking) NPN transistor is connected additionally to the output. This transistor operates in a saturated region. Because the NPN sink switch sorts the output terminal to ground when the applied flux density is greater than that of the ON-preset point.


The output switching transistor can take the form of an open emitter transistor, an open collector transistor configuration, or a combination of both. This setup enables a push-pull output type configuration that has the capacity to sink sufficient current to directly power various loads such as relays, motors, LEDs, and lamps.



General Sensor Baser Hall Effect
General Sensor Baser Hall Effect

Let's compare current transducers, capacitive sensors, and Hall Effect sensors in terms of similarities and differences.


Similarities


  1. Sensor Nature: All three are sensors designed to detect and measure specific physical phenomena.

  2. Contactless Operation: Like the Hall Effect sensor, both current transducers and capacitive sensors can operate without physical contact with the measured object, ensuring non-intrusive and wear-free sensing.

  3. Electronic Output: These sensors provide electronic output signals that can be further processed by electronic circuits or systems for various applications.


Differences


Physical Phenomenon Measured


  • Current Transducer: Measures electric current flowing through a conductor. It usually involves converting the magnetic field produced by the current into a measurable signal.

  • Capacitive Sensor: Measures changes in capacitance, which is influenced by the proximity or dielectric properties of objects.

  • Hall Effect Sensor: Detects and measures magnetic fields, utilizing the Hall Effect in semiconductors.


Applications


  • Current Transducer: Primarily used in applications where monitoring and control of electric current are critical, such as in power systems, electric vehicles, and industrial automation.

  • Capacitive Sensor: Commonly employed in proximity sensing, level detection, and touchscreens. Applications range from smartphones to industrial automation.

  • Hall Effect Sensor: Used for position sensing, speed detection, and current sensing. Applications include automotive systems (ABS), brushless DC motor control, and magnetic field measurement.


Working Principle


  • Current Transducer: Operates based on the principles of electromagnetic induction or the Hall Effect to convert current into a measurable signal.

  • Capacitive Sensor: Relies on changes in capacitance due to the proximity or dielectric properties of objects.

  • Hall Effect Sensor: Detects the effect of a magnetic field on a semiconductor, producing a voltage proportional to the magnetic flux density.


Physical Structure


  • Current Transducer: Can take the form of toroidal cores or hall-effect sensors embedded in the current path.

  • Capacitive Sensor: Typically consists of two conductive plates separated by a dielectric material.

  • Hall Effect Sensor: Comprises a semiconductor material with a current flowing through it, perpendicular to an applied magnetic field.


Sensitivity


  • Current Transducer: Sensitive to changes in the magnetic field produced by the current flowing through a conductor.

  • Capacitive Sensor: Sensitive to changes in capacitance influenced by the dielectric properties of the nearby objects.

  • Hall Effect Sensor: Sensitive to changes in magnetic fields.


While these sensors share the general trait of being electronic devices used for sensing, they differ significantly in terms of the physical phenomena they measure, applications, working principles, and structural designs.


The Hall Effect sensor is a versatile electronic device that has found its way into various applications due to its unique working principle. Here, we delve into a detailed exploration of its advantages, disadvantages, limitations, and applications.


Advantages of Hall Effect Sensor


Contactless Operation

  • The Hall Effect sensors function without the need for direct contact with the object being measured. This feature eliminates issues related to wear and tear, increasing their reliability and longevity.

Long Operational Life

  • The absence of mechanical components subject to friction contributes to the long operational life of Hall Effect sensors, making them suitable for demanding and continuous-use applications.

High Reliability

  • Hall Effect sensors offer accuracy and reliability in their measurements. This attribute is especially vital in use cases that require a high level of accuracy, such as in industrial automation and control systems.

Low Power Consumption

  • These sensors typically have low power requirements, rendering them energy-efficient. This feature is advantageous in battery-powered devices and portable applications.

Compact Size

  • Hall Effect sensors can be designed in compact sizes, facilitating integration into systems with limited space. This attribute is particularly beneficial in applications where size constraints are a critical consideration.

Wide Operating Temperature Range

  • Hall Effect sensors exhibit a broad operating temperature range, making them suitable for deployment in diverse environmental conditions, from extreme cold to high heat.

Fast Response Time

  • The sensors offer rapid response times, making them well-suited for applications that demand quick sensing and prompt feedback, such as in motor control systems.


Disadvantages of Hall Effect Sensor


Temperature Sensitivity

  • Despite their ability to operate in a wide temperature range, Hall Effect sensors can exhibit some sensitivity to temperature variations. This sensitivity may introduce errors in applications requiring high precision.

Cost

  • Hall Effect sensors can be more expensive compared to some traditional sensors. The higher cost may limit their use in applications where cost-effectiveness is a primary concern.

Complex Signal Conditioning

  • The output signal from Hall Effect sensors might require complex signal conditioning to obtain the desired information. This complexity could increase system design and implementation efforts.


Limitations of Hall Effect Sensor


Magnetic Field Dependency

  • Hall Effect sensors rely on the presence of a magnetic field. The accuracy and performance of these sensors can be influenced by the strength and orientation of the magnetic field, posing a limitation in certain applications.

Limited Sensing Range

  • Hall Effect sensors may have a limited sensing range, restricting their use in applications that require sensing over long distances.

External Magnetic Fields

  • External magnetic fields can interfere with Hall Effect sensor readings, leading to inaccuracies in certain situations. Shielding or careful placement may be required to mitigate these effects.


Applications of Hall Effect Sensor


Position Sensing

  • Hall Effect sensors are widely employed for position sensing in applications such as automotive throttle position sensing, rotary encoders, and gear position sensing.

Current Sensing

  • These sensors find use in current sensors for measuring electric current in electronic circuits, ensuring precise monitoring and control.

Speed Sensing

  • Hall Effect sensors are integral in detecting the speed of rotating objects, such as in motor control applications and conveyor systems.

Proximity Detection

  • They are utilized in proximity detection systems, like in smartphones for detecting the closing of flip covers or in security systems for intrusion detection.

Magnetic Field Measurement

  • Hall Effect sensors are employed for measuring magnetic fields in scientific research, industrial processes, and geophysical applications.

Anti-lock Braking Systems (ABS)

  • In automotive systems, Hall Effect sensors play a crucial role in ABS, monitoring wheel speed to prevent skidding during braking.

Brushless DC Motors

  • Hall Effect sensors are fundamental in the commutation of brushless DC motors, ensuring efficient and precise control of motor operation.


In conclusion, Hall Effect sensors offer a combination of advantages and disadvantages, making them suitable for specific applications where their characteristics align with the requirements of the system. Understanding these aspects is crucial for effectively implementing Hall Effect sensors in diverse technological applications.


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