Hall Effect: Definition, Principle, Measurement Methods

Ⅰ. What is the Hall Effect?

The interaction of the matching electric and magnetic fields of charged particles, such as electrons, results in the Hall effect. The Hall effect principle is illustrated in the following animation for a clearer understanding.

Figure. 1

Ⅱ. Hall effect principle

Current starts to flow when the conductive plate is linked to a circuit with a battery. From one end of the plate to the other, the charge carriers will move in a straight line. A magnetic field is produced by the passage of charge carriers. The magnetic field of the charge carriers is altered when the magnet is put close to the plate. The straight-line flow of charge carriers is hampered as a result. The Lorentz force is the force that alters the direction of the flow of charge carriers.

Positively charged holes will be deflected to one side of the plate and negatively charged electrons will be diverted to the opposite side of the plate as a result of the distortion of the charge carrier magnetic field.The Hall voltage, which may be measured using a meter, is the potential difference that is produced between the two sides of the plate.

Figure. 2

The magnetic field perpendicular to the conducting plate is represented by blue arrow B in the Hall effect and Lorentz force equation.

According to the Hall effect concept, a voltage can be measured where the current path is at a right angle when a current-carrying conductor or semiconductor is inserted into a vertical magnetic field.

The following formula yields the Hall voltage, written as VH:

Hall Voltage Formula:

On the conducting plate, VH stands for the Hall voltage.

Figure. 3

The sensor's current is denoted by the symbol I.

The magnetic field intensity is B.

The charge is q.

The number of charge carriers per volume unit is n.

The sensor's thickness is d.

Principle of Hall Effect Sensors

The sensor detects it and generates an output voltage known as the Hall voltage VH when the magnetic flux density in the area surrounding the sensor reaches a certain threshold. The ensuing figure illustrates the particular principle.

A small rectangular slice of p-type semiconductor material, such as gallium arsenide (GaAs), indium antimonide (InSb), or indium arsenide (InAs), that carries a continuous current is the basic building block of a Hall-effect sensor.

Figure. 4

Ⅲ. Hall Effect Sensor Schematic

The magnetic flux lines acting on the semiconductor material in a Hall-effect sensor cause charge carriers, electrons, and holes to be deflected to either side of the semiconductor plate. The magnetic field that charge carriers encounter as they go through the semiconductor material is what causes this movement.

Due to the accumulation of these charge carriers when the electrons and holes flow sideways, there is a potential difference between the two sides of the semiconductor material. An external magnetic field at right angles to the semiconductor material then affects the flow of the electrons through it; this effect is stronger in flat rectangular materials.

The magnetic field's strength and the sort of magnetic pole are both revealed by the Hall effect. For instance, a south pole would result in a voltage output from the device, whereas a north pole would have no impact. In the absence of a magnetic field, Hall effect sensors and switches are typically built to be "off" (open circuit states). They can only "open" (become closed-circuit) when exposed to a magnetic field with enough power and polarity.

Ⅳ. Hall Effect Sensor

The sensor functions as an analog sensor in its most basic form, directly returning voltage. Its separation from the Hall plate can be calculated with the aid of a known magnetic field. The relative position of the magnets can be determined using the sensor set.

Hall effect sensors are frequently used in conjunction with circuitry that enables the device to operate in digital (on/off) mode; in this arrangement, they may be referred to as switches. The change in light is readily visible in the image below, which depicts a wheel holding two magnets moving through a Hall effect sensor.

Figure. 5 A wheel containing two magnets passes a Hall effect sensor

Because most Hall effect devices only have a very tiny output drive capacity—between 10 and 20 mA—they are unable to switch big electrical loads directly. Add an open collector (current sinking) NPN transistor to the output for high current loads. As displayed below

When the applied magnetic flux density is greater than the "ON" preset value, the transistor behaves as an NPN sink current switch, shorting the output terminal to ground.

Relays, motors, LEDs, lights, and other loads can all be driven directly by the output switching transistors in a push-pull output configuration whether they are configured as open-emitter transistors, open-collector transistors, or both.

Figure. 6 Typical Hall Effect Switch Diagram

Linear or digital outputs are provided for Hall-effect sensors. The output voltage of a linear (analog) sensor is proportional to the magnetic field passing through the Hall sensor, and the output signal is directly obtained from the output of the op amp. The Hall voltage at the output is：

Figure. 7 Hall voltage formula diagram

Hall voltage is expressed in volts as V H.

The Hall effect coefficient is R H.

I is the amount of current (in amps) passing through the sensor.

T is the sensor's thickness in millimeters.

B is the magnetic flux density for Tesla.

A continuous voltage output is produced by linear or analog sensors, and it rises in the presence of powerful magnetic fields and falls in the presence of weak ones. As the magnetic field intensity rises in a linear output Hall effect sensor, the output signal from the amplifier rises as well until the supplied power supply's constraints cause it to saturate.

Any further expansion of the magnetic field will saturate the output further rather than having any impact on it.

Ⅴ. Hall Sensor Measurement Method--Motion Path of Magnetic Field

In many applications, a single permanent magnet fastened to a rotating shaft or other device can be used to operate Hall effect sensors, which are activated by a magnetic field. Magnet movements can take many different forms, including inductive movements like "frontal," "sideways," "push-pull," or "push-push."

The magnetic flux lines in each configuration must always be perpendicular to the device's sensing region and have the right polarity to guarantee maximum sensitivity.

In order to provide substantial field strength variations for the desired motion, high field strength magnets are also necessary to assure linearity. Two of the more popular sensing setups employing a single magnet are frontal detection and sideways detection. There are numerous different courses of motion for detecting magnetic fields.

1. Front detection Hall sensor measuring method

As the term "frontal detection" suggests, it is necessary for the magnetic field to be perpendicular to the Hall-effect sensing device and directed toward the active face proximity sensor in order to detect something. a "positive" strategy.

Figure. 8

In a linear device, this frontal method generates an output signal, VH, which represents the magnetic field intensity, or flux density, as a function of proximity to the Hall-effect sensor. The magnetic field is stronger and the output voltage is higher at closer distances and vice versa.

Positive and negative magnetic fields can also be distinguished using linear devices. To signal position detection, the nonlinear device can turn on the output at a predetermined air gap distance from the magnet.

2. Sideways detection in the Hall sensor measuring method

The second type of sensing is called "lateral detection". The magnets must be moved laterally over the Hall effect element's surface to accomplish this.

For example, to determine the rotational speed of a spinning magnet or motor, sideways or slip-through detection can be used to detect the presence of a magnetic field when the magnetic field crosses the surface of the Hall element within a defined air gap distance.

Figure. 9

Positive and negative outputs can be represented by linear output voltages, depending on where the magnetic field crosses the sensor's zero-field centerline. This enables the detection of directional motion, which may be vertical or horizontal.

Ⅵ. Position Detector with Hall Sensor

There are numerous ways to link Hall-effect sensors to electrical and electronic circuits, depending on the type of device (whether digital or linear). Below is an example that is really basic and straightforward to construct:

Figure. 10 Position Detector

The frontal position detector will be in the "off" position when there is no magnetic field (0). The device will "switch on" and illuminate the LED when the south pole of the permanent magnet (positive Gaussian) moves vertically within the active region of the Hall effect sensor. The Hall effect sensor will remain "ON" once it has been toggled.

Ⅶ. Advantages and disadvantages of hall sensor

Advantage

Electronic switches can be created using hall effect sensors.

1. These switches are more dependable and less expensive than mechanical switches.

2. It can function at up to 100 kHz of frequency.

3. Since solid state switches with hysteresis are utilized in place of mechanical contacts, contact bounce is not an issue.

4. The sensor is not impacted by environmental contaminants because it is hermetically sealed when it is sent. It can therefore be used in challenging circumstances.

For linear sensors, Hall effect sensors, and measuring magnetic field strength:

1. Able to measure a variety of magnetic fields

2. Can measure magnetic fields to the north or south.

3. Possibly flat

Disadvantages

Compared to fluxgate magnetometers or magnetoresistive-based sensors, Hall-effect sensors have substantially lower measurement precision. Hall-effect sensors also need to be compensated for their substantial drift.