Basic Introduction to Hall Effect Sensors

Catalog

Ⅰ Introduction

The Hall effect sensor is a magnetic field sensor made according to the Hall effect. The Hall effect is a type of magnetoelectric effect. This phenomenon was discovered by Hall (A.H. Hall, 1855-1938) in 1879 when he studied the conductive mechanism of metals. Later, it was found that semiconductors, conductive fluids, etc. also have this effect, and the Hall effect of semiconductors is much stronger than metals. Various Hall elements made using this phenomenon are widely used in industrial automation technology, detection technology, and information processing, etc. The Hall effect is a basic method for studying the performance of semiconductor materials. The Hall coefficient measured by the Hall effect experiment can determine important parameters such as the conductivity type, carrier concentration, and carrier mobility of semiconductor materials.

Ⅱ How does a hall sensor work?

According to the principle of the Hall effect, the size of the Hall potential depends on Rh, the Hall constant, which is related to the semiconductor material; I, the bias current of the Hall element; B, the magnetic field strength; d, the thickness of the semiconductor material.

For a given Hall device, when the bias current I is fixed, UH will completely depend on the measured magnetic field strength B.

A Hall element generally has four terminals, two of which are the input terminals of the bias current I of the Hall element, and the other two are the output terminals of the Hall voltage. If the two output terminals form an external loop, a Hall current will be generated. Generally speaking, the setting of the bias current is usually given by an external reference voltage source. If the accuracy requirements are high, the reference voltage source is replaced by a constant current source. In order to achieve high sensitivity, some Hall elements are equipped with coated alloys with high magnetic permeability; the Hall potential of this type of sensor is large, but the saturation occurs around 0.05T.

Figure1. Hall effect

A control current I is applied to both ends of the semiconductor sheet, and a uniform magnetic field with a magnetic induction strength of B is applied in the vertical direction of the sheet, then a Hall voltage with a potential difference of UH will be generated in the direction perpendicular to the current and magnetic field.

There is a Hall semiconductor chip in the magnetic field, and a constant current I passes from A to B through the chip. Under the effect of the Lorentz force, the electron flow of I is shifted to one side when passing through the Hall semiconductor, causing the potential difference of the sheet in the CD direction, which is the so-called Hall voltage.

The Hall voltage changes with the strength of the magnetic field. The stronger the magnetic field, the higher the voltage. The weaker the magnetic field, the lower the voltage. The Hall voltage is very small, usually only a few millivolts, but it is amplified by the amplifier in the integrated circuit. The voltage can be amplified enough to output a stronger signal. If the Hall IC is used as a sensor, a mechanical method is required to change the magnetic induction intensity. The method shown in the figure below uses a rotating impeller as a switch to control the magnetic flux. When the impeller blade is in the air gap between the magnet and the Hall IC, the magnetic field deviates from the integrated chip and the Hall voltage disappears. In this way, the change in the output voltage of the Hall IC can indicate a certain position of the impeller drive shaft. Using this working principle, the Hall IC chip can be used as the ignition timing sensor. The Hall effect sensor is a passive sensor. It needs an external power supply to work. This feature allows it to detect low-speed operation.

Fgure2. Hall effect sensor

1-Hall semiconductor materials element 2-Permanent magnet 3-Blade blocking magnetic field line

Ⅲ Hall Effect

Applying a magnetic field perpendicular to the direction of the current on the semiconductor will cause the electrons and holes in the semiconductor to gather in different directions under the Lorentz force in different directions, and an electric field will be generated between the accumulated electrons and holes. After the force balances with the Lorentz force, it no longer gathers. At this time, the electric field will subject the subsequent electrons and holes to the electric field force and balance out the Lorentz force generated by the magnetic field. The holes can pass smoothly without shifting, this phenomenon is called the Hall effect. The built-in voltage generated is called the Hall voltage.

The Hall effect is particularly important in applied technology. Hall discovered that if a current (Iv) is applied to a conductor (d) located in a magnetic field (B), the direction of the magnetic field is perpendicular to the direction of the applied voltage, then it is both perpendicular to the magnetic field and perpendicular to the direction of the applied current Another voltage (UH) will be generated in the direction of. The voltage is called the Hall voltage. This phenomenon is called the Hall effect. It's like a road. Everyone was evenly distributed on the road and moved forward. When there is a magnetic field, everyone may be pushed to the right of the walk. There will be a voltage difference on both sides of the road (conductor). This is called the "Hall effect". The Hall device made according to the Hall effect is to use the magnetic field as the working medium to convert the motion parameters of the object into the form of digital voltage output, so that it has the functions of sensing and switching.

So far, Hall devices that have been widely used in modern automobiles include signal sensors on distributors, speed sensors in ABS systems, car speedometers and odometers, liquid physical quantity detectors, and currents of various electrical loads detection and diagnosis of working conditions, engine speed and crank angle sensors, various switches, etc.

Ⅳ Classification of Hall effect sensor

Hall effect sensors are divided into linear Hall effect sensors and switch Hall effect sensors.

(1) The switch-type Hall effect sensor is composed of a voltage regulator, Hall elements, a differential amplifier, a Schmitt trigger, and an output stage, which outputs a digital quantity. There is also a special form of the switch-type Hall effect sensor, called the lock-type Hall effect sensor.

(2) The linear Hall effect sensor is composed of Hall elements, a linear amplifier, and an emitter follower, which outputs analog quantity.

Linear Hall effect sensors can be divided into open-loop and closed-loop. The closed-loop Hall effect sensor is also called the zero flux Hall effect sensor. Linear Hall effect sensors are mainly used for AC and DC current and voltage measurement.

1. Switch type

As shown in Figure 3, where Bnp is the magnetic induction intensity at the operating point "on" and BRP is the magnetic induction intensity at the release point "off". When the applied magnetic induction intensity exceeds the action point Bnp, the sensor outputs a low level. When the magnetic induction intensity drops below the action point Bnp, the sensor output level does not change, and the sensor will go from low level until it drops to the release point BRP to a high level. The hysteresis between Bnp and BRP makes the switching action more reliable.

Figure3. Switch type Hall sensor

2. Key type

As shown in Figure4, when the magnetic induction intensity exceeds the operating point Bnp, the sensor output changes from high level to a low level. After the external magnetic field is cancelled, its output state remains unchanged (that is, the latched state), and only when the magnetic induction intensity reaches BRP can the level be changed.

Figure4. Key type Hall sensor

3. Linear type

The output voltage has a linear relationship with the applied magnetic field strength. As shown in Figure5, it can be seen that there is good linearity in the range of magnetic induction intensity of B1 to B2. When the magnetic induction intensity exceeds this range, it is saturated.

Figure5. Linear type Hall sensor

4. Open-loop current sensor

Because there is a magnetic field inside the energized solenoid, its size is proportional to the current in the wire, so the Hall effect sensor can be used to measure the magnetic field to determine the size of the current in the wire. Using this principle, the Hall current sensor can be designed and manufactured. The advantage of the Hall effect sensor is that it does not make electrical contact with the circuit under test. So it does not affect the circuit under test and does not consume the power of the power supply under test, and is particularly suitable for large current sensing.

The working principle of the Hall current sensor is shown in Figure. The standard ring core has a gap. Insert the Hall effect sensor into the gap. The ring is wound with a coil. When the current passes through the coil, a magnetic field is generated and the Hall effect sensor has a signal output.

5. Closed-loop current sensor

The magnetic balance current sensor is also called Hall closed-loop current sensor, also known as the compensation sensor. The magnetic field generated by the measured current Ip of the main loop at the magnetic ring passes through a secondary coil so that the Hall device is in the working state of detecting zero magnetic flux.

The specific working process of the magnetic balance current sensor is: when a current passes through the main loop, the magnetic field generated on the wire is collected by the magnetic ring and induced on the Hall device, and the generated signal output is used to drive the corresponding power tube to obtain a compensation current Is. This current then generates a magnetic field through the multi-turn winding, which is exactly the opposite of the magnetic field generated by the measured current, thus compensating for the original magnetic field and gradually reducing the output of the Hall device. When the magnetic field generated by multiplying Ip and the number of turns is equal, Is no longer increases, and the Hall device at this time plays the role of indicating zero magnetic flux, which can be balanced by Is. Any change in the measured current will disrupt this balance. Once the magnetic field is out of balance, the Hall device has signal output. Immediately after power amplification, a corresponding current flows through the secondary winding to compensate for the unbalanced magnetic field. The time required from magnetic field imbalance to re-equilibrium is theoretically less than 1μs, which is a dynamic balancing process.　　

Figure6. Closed-loop current sensor

Ⅴ Advantages of Hall effect sensor

1. Hall effect sensors can measure arbitrary waveforms of current and voltage, such as DC, AC, and pulse waveforms, and even the transient peaks. The secondary current faithfully reflects the waveform of the primary current. The ordinary transformer is incomparable, it is generally only suitable for measuring 50Hz sine wave;

2. There is good electrical isolation between the primary circuit and the secondary circuit, and the isolation voltage can reach 9600Vrms;

3. High accuracy: The accuracy is better than 1% in the working temperature range, which is suitable for the measurement of any waveform;

4. Good linearity: better than 0.1%;

5. Wide bandwidth: The rise time of the high-bandwidth current sensor can be less than 1μs; however, the bandwidth of the voltage sensor is narrow, generally within 15kHz, the rise time of the 6400Vrms high-voltage voltage sensor is about 500uS, and the bandwidth is about 700Hz.

6. Measurement range: Hall effect sensors are series products, current measurement can reach 50KA, voltage measurement can reach 6400V.

Ⅵ Applications of Hall effect sensor

1. Hall effect sensor technology used in the automotive industry

Hall effect sensor technology has a wide range of applications in the automotive industry, including power, body control, traction control, and anti-lock braking systems. In order to meet the needs of different systems, Hall effect sensors have three types which are switch, analog, and digital sensors.

Hall effect sensors can be made of metals, semiconductors, etc. The quality of the Hall effect depends on the material of the conductor, which directly affects the positive ions and electrons flowing through the sensor. When manufacturing Hall elements, the automotive industry generally uses three semiconductor materials, namely gallium arsenide, indium antimonide, and indium arsenide. The most commonly used semiconductor material is indium arsenide.

The form of the Hall effect sensor determines the difference of the amplifier circuit, and its output should be adapted to the device to be controlled. This output may be analogs, such as an acceleration position sensor or throttle position sensor, or it may be digital such as crankshaft or camshaft position sensor.

When the Hall element is used for an analog sensor, this sensor can be used for a thermometer in an air-conditioning system or a throttle position sensor in a power control system. The Hall element is connected to the differential amplifier, and the amplifier is connected to the NPN transistor. The magnet is fixed on the rotating shaft. When the shaft rotates, the magnetic field on the Hall element is strengthened. The Hall voltage it produces is proportional to the strength of the magnetic field.

When the Hall element is used for digital signals, such as a crankshaft position sensor, camshaft position sensor, or vehicle speed sensor, the circuit must be changed first. The Hall element is connected to the differential amplifier, and the differential amplifier is connected to the Schmitt trigger. In this configuration, the sensor outputs an on or off signal. In most automotive circuits, Hall effect sensors are current sinks or ground signal circuits. To accomplish this, an NPN transistor is required to be connected to the output of a Schmitt trigger. The magnetic field passes through the Hall element, and the blade on a trigger wheel passes between the magnetic field and the Hall element.

2. Hall effect sensor applied to taxi meter

The application of the Hall effect sensor to the taximeter: the signal detected by the Hall effect sensor A44E installed on the wheel is sent to the single-chip microcomputer. After processing and calculating, and sent to the display unit, thus completing the mileage calculation. P3.2 port is used as the input terminal of the signal, and the external interrupt 0 is used internally. Every time the wheel turns (the wheel circumference is 1 m), the Hall switch detects and outputs the signal, causing the interruption of the microcontroller. When the pulse counting reaches 1 000 times, that is, 1 km, the single-chip microcomputer controls to automatically increase the amount.

Whenever the Hall effect sensor outputs a low-level signal, the microcontroller is interrupted once. When the mileage counter counts the mileage pulses for 1 000 times, a program accumulates the current total, and the microcomputer enters the mileage counting interrupt service program. In this program, it is necessary to complete the accumulation operation of the current mileage and total amount, and store the result in the mileage and total amount register.

3. Hall current sensor used in frequency converter

A magnetic field is induced around the wire through which the current flows, and then the Hall device is used to detect the magnetic field induced by the current, and the magnitude of the current that generates this magnetic field can be measured. Thus, Hall current and voltage sensors can be constructed. Because the output voltage of the Hall device is proportional to the product of the magnetic induction applied to it and the working current flowing through it, it is a device with a multiplier function and can be directly interfaced with various logic circuits and can also be directly driven loads of various nature. Because the application principle of the Hall device is simple, the signal processing is convenient, and the device itself has a series of unique advantages, it also plays a very important role in the inverter.

In frequency converters, the main role of Hall current sensors is to protect expensive high-power transistors. Because the response time of the Hall current sensor is shorter than 1μs, when an overload short circuit occurs, the power can be cut off before the transistor reaches the limit temperature.

Hall current sensor can be divided into direct measurement type and zero magnetic formula according to its working mode. In the inverter, because of the need for precise control and calculation, the zero magnetic flux method is selected. Amplifying the output voltage of the Hall device, and then amplifying the current. This current passes through the compensation coil, and the magnetic field is generated by the compensation coil and the magnetic field generated by the measured current in the opposite direction. If the condition IoN1=IsN2 is met, then the magnetic flux in the core is 0, then the following formula holds:

Io=Is(N2/N1)

In the formula, Io is the measured current, that is, the current in the primary winding in the magnetic core. N1 is the number of turns in the primary winding. Is is the current in the compensation winding, and N2 is the number of turns in the compensation winding. It can be known from the above formula that when the magnetic balance is reached, Io can be obtained from Is and the turns ratio N2/N1.

The hall current sensor is characterized by the "potential-free" detection of current. That is, the measurement circuit can realize current detection without accessing the circuit under test, and they are coupled by the magnetic field. Therefore, the input and output circuits of the detection circuit are completely electrically isolated. During the detection process, the detection circuit and the detected circuit do not affect each other.

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