Hall sensor

Principle 1

According to the principle of Hall effect, the magnitude of the Hall potential depends on: Rh is the Hall constant, which relates to the semiconductor material; I is the bias current of the Hall element; B is the strength of the magnetic field; d is 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 lead-out 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 outer loop, 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, Hall sensors are equipped with permalloy with high magnetic permeability on the sensing surface of the Hall element. The Hall potential of this type of sensor is relatively large, but it saturates around 0.05T. It is only applicable to the low limit. For use on a small scale.

Controlled current I is applied to both ends of the semiconductor sheet, and a uniform magnetic field having a magnetic induction intensity of B is applied in the vertical direction of the sheet. In the direction perpendicular to the current and the magnetic field, a Hall voltage having a potential difference of UH is generated.

2 working principle

There is a Hall semiconductor wafer in the magnetic field, and a constant current I passes through the wafer from A to B. Under the action of the Lorentz force, the electron flow of I is shifted to one side when passing through the Hall semiconductor, so that the sheet produces a potential difference in the CD direction, which is the so-called Hall voltage.
The Hall voltage changes with the magnetic field strength. 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 amplified by the amplifier in the integrated circuit. This voltage can be amplified enough to output a stronger signal. If Hall ICs are used for sensing, it is necessary to use mechanical methods to change the magnetic induction. The method shown in the following figure 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 of 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 to act on the ignition timing sensor. Hall effect sensors are passive sensors that require an external power source to operate. This feature makes it possible to detect low operating speeds.

3 Hall Effect

The Hall effect is essentially the deflection of a moving charged particle by a Lorentz force in a magnetic field. When charged particles (electrons or holes) are confined in the solid material, this deflection results in the accumulation of positive and negative charges in the direction of the vertical current and magnetic field, thereby creating an additional transverse electric field. For the semiconductor sample shown in Fig. 1, if the current Is is applied in the X direction and the magnetic field B is applied in the Z direction, then the opposite charges are accumulated in the Y direction, that is, on both sides of the A and A' electrodes of the sample, and the corresponding charges are generated. Additional electric field. The direction of the electric field is determined by the electrical type of the sample. Obviously, the electric field is to prevent the carrier from further shifting to the side. [1] When the horizontal electric field force eEH of the carrier is equal to the Lorentz force, the charge accumulation on both sides of the sample will reach equilibrium, so there are (1) EH is the Hall electric field, and V is the average drift speed of carriers in the current direction. Let the width of the sample be b, the thickness be d, the carrier concentration is n, then (2) can be obtained by (1), (2) two types (3); that is Hall voltage VH (voltage between A and A′ electrodes) and ISB product It is proportional to the thickness d of the sample. The proportional coefficient is called the Hall coefficient. It is an important parameter that reflects the Hall effect of the material. As long as the VH (volt) is measured and the IIs (ampere), B (gaussian) and d (cm) are known, the RH can be calculated as follows. (cm 3 / Coulomb).

4 elements

According to the Hall effect, a component made of a semiconductor material is called a Hall element. It has the advantages of being sensitive to magnetic field, simple structure, small volume, wide frequency response, large output voltage change, long service life, etc. Therefore, it has been widely used in measurement, automation, computer and information technology.

Category 5

Hall sensors are classified into linear Hall sensors and switch Hall sensors.

(a) The switching Hall sensor consists of a voltage regulator, a Hall element, a differential amplifier, a Schmitt trigger, and an output stage, which outputs digital quantities. Switch Hall sensors also have a special form, called a key-type Hall sensor.

(b) Linear Hall sensors consist of Hall elements, linear amplifiers, and emitter followers, which output analog quantities.

Linear Hall sensors can be divided into open-loop and closed-loop. Closed-loop Hall sensors, also known as zero flux Hall sensors. Linear Hall sensors are mainly used for AC and DC current and voltage measurements. .

Switch type

Bnp is the magnetic induction intensity of the "open" operating point, and BRP is the magnetic induction intensity of the release point "off". When the applied magnetic induction intensity exceeds the operating point Bnp, the sensor outputs a low level. When the magnetic induction intensity drops below the operating point Bnp, the sensor output level does not change, and the sensor will only be lowered by the release point BRP. Jumps high. The lag between Bnp and BRP makes switching more reliable.

Lock type

When the magnetic induction intensity exceeds the operating point Bnp, the sensor output transitions from a high level to a low level, and after the external magnetic field is withdrawn, the output state remains unchanged (ie, the latched state), and when the reverse magnetic induction intensity must be applied to reach the BRP Can make the level change.

Linear type

The output voltage has a linear relationship with the applied magnetic field strength.

Open-loop current sensor

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

The working principle of the Hall current sensor is shown in Fig. 6. The standard ring core has a notch. The Hall sensor is inserted into the notch. The ring is wound with a coil. When the current passes through the coil, a magnetic field is generated. The Hall sensor has a signal. Output.

Closed loop current sensor

Magnetic balance current sensor is also called Hall closed-loop current sensor, also called compensation sensor, that is, the magnetic field generated by the main loop measured current Ip at the polymagnetic ring is compensated by a secondary coil, and the magnetic field generated by the current compensates. The Hall device is in the state of detecting the zero magnetic flux.

The specific working process of the magnetic balance type current sensor is as follows: when a current passes through the main circuit, the magnetic field generated on the wire is gathered by the polymagnetic ring and sensed on the Hall device, and the generated signal output is used to drive the corresponding power tube and It is turned on to obtain a compensation current Is. This current, in turn, generates a magnetic field through multiple windings that oppose 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 is no longer increased. At this time, the Hall device serves to indicate zero magnetic flux. At this time, it can be balanced by Is. Any change in the measured current will destroy this balance. Once the magnetic field is out of balance, the Hall device has a signal output. Immediately after power amplification, a corresponding current flows through the secondary winding to compensate for the imbalanced magnetic field. From the magnetic field imbalance to the rebalancing, the required time is theoretically less than 1μs, which is a dynamic equilibrium process.

6 advantages

1, Hall sensors can measure arbitrary waveforms of current and voltage, such as: DC, AC, pulse waveform, and even the measurement of transient peaks. The secondary current faithfully reflects the waveform of the primary current. The common transformer is not comparable with it, it is generally only suitable for measuring 50Hz sine wave;

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

3, high precision: in the working temperature area accuracy is better than 1%, the accuracy is suitable for any waveform measurement;

4, good linearity: better than 0.1%;

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

6. Measurement range: Hall sensor is a series of products, current measurement up to 50KA, voltage measurement up to 6400V.

When using a Hall current sensor, follow these precautions:

1. In order to obtain better dynamic characteristics and sensitivity, it is necessary to pay attention to the coupling of the primary coil and the secondary coil. To achieve good coupling, it is better to use a single wire and the wire completely fills the hole of the Hall sensor module.

2, when the use of large DC current flowing through the sensor primary coil, and the secondary circuit is not connected to the power | regulator or secondary side open circuit, then the magnetic circuit is magnetized, resulting in remanence, affecting the measurement accuracy (So When using, please turn on the power supply and measurement terminal M). When this happens, demagnetization must be performed first. The method is that the secondary circuit does not add power, but in the primary coil, an alternating current of the same level is passed and its value is gradually reduced.

3, Hall sensors have strong resistance to external magnetic field interference, but in order to obtain high measurement accuracy, when there is a strong magnetic field interference, appropriate measures must be taken to solve. The usual methods are:

Adjust the direction of the module so that the influence of the external magnetic field on the module is minimized;

The module is covered with a magnetic shield metal shield.

4, the best measurement accuracy is obtained under the rated value, when the measured current is much lower than the rated value, to obtain the best accuracy, the primary side can be used more, but need to pay attention to the spatial position of the wire (see One).

7 uses

Hall devices have many advantages, they have a solid structure, small size, light weight, long life, easy installation, low power consumption, high frequency (up to 1MHZ), shock resistance, not afraid of dust, oil, water vapor and salt mist, etc. Pollution or corrosion.

Hall linear devices have high accuracy and linearity; Hall switches have no contact, no wear, clear output waveform, no jitter, no rebound, and high position repeat accuracy (up to μm). Hall devices with various compensation and protection measures have a wide operating temperature range of -55°C to 150°C.

According to the nature of the detected objects, their applications can be divided into: direct application and indirect application. The former is to directly detect the magnetic field or magnetic property of the object under test, and the latter is to detect the magnetic field set by the object under inspection, and use this magnetic field as a carrier of the detected information, through which many non-electrical, non-magnetic The physical quantities such as force, moment, pressure, stress, position, displacement, speed, acceleration, angle, angular velocity, revolution number, rotation speed, and time when the working state changes, etc., are converted into electricity to perform detection and control.

Displacement measurement

The two permanent magnets are placed opposite to each other, and the linear Hall sensor is placed in the middle. The magnetic induction intensity is zero. This point can be used as the zero point of the displacement. When the Hall sensor is used to make a â–³Z displacement on the Z axis, the sensor has A voltage output, the voltage magnitude is proportional to the size of the displacement.

Force measurement

If the tension, pressure and other parameters become displacement, it can measure the size of tension and pressure, according to this principle can be made of force sensors.

Angular speed measurement

A piece of magnet is glued on the side of the non-magnetic material disc. The Hall sensor is placed near the edge of the disc. The disc rotates once. The Hall sensor outputs a pulse, so that the revolution number (counter) can be measured. Into the frequency meter, you can measure the speed.

Linear velocity measurement

If the switch type Hall sensor is regularly arranged on the track at a predetermined position, a pulse signal can be measured from the measurement circuit when a permanent magnet mounted on the moving vehicle passes through it. The speed of the vehicle can be measured based on the distribution of the pulse signal.

8 Precautions

(1) The current sensor must be properly selected according to the rated effective value of the measured current. If the measured current is excessive for a long time, the final power amplifier tube (magnetic compensation type) will be damaged. Under normal circumstances, the duration of the 2 times overload current should not exceed 1 minute.

(2) The voltage sensor must be connected in series with a current limiting resistor R1 according to the product specification so that the primary side can obtain the rated current. Under normal circumstances, the 2 times overvoltage duration must not exceed 1 minute.

(3) The best accuracy of the current and voltage sensors is obtained under the condition of the primary side rated value, so when the measured current is higher than the rated value of the current sensor, a correspondingly large sensor should be selected; when the measured voltage is higher than the voltage sensor When rated, the current limiting resistor should be readjusted. When the measured current is less than 1⁄2 of the nominal value, multiple turns can be used for best accuracy.

(4) The sensor with 3KV insulation withstand voltage can work normally in 1KV and below AC systems and 1.5KV and below DC systems. 6KV sensors can work normally in 2KV and below AC systems and 2.5KV and below DC systems. , Be careful not to use overpressure.

(5) When used on devices that require good dynamic characteristics, it is best to use a single copper-aluminum busbar and match the borehole diameter. Larger or smaller turns will affect the dynamic characteristics.

(6) When used in a high-current DC system, for some reason, the power supply is open or fails, and the iron core has a large remanence, which is worth noting. Remanence affects accuracy. The method of demagnetization is to not increase the power supply, pass an alternating current in the primary side and gradually reduce its value.

(7) The sensor is resistant to external magnetic field: a distance of 5 to 10cm from the sensor, which is more than 2 times the current value of the primary side of the sensor, can produce resistance to the magnetic field. When three-phase high-current wiring, the distance between phases should be greater than 5 ~ 10cm.

(8) In order to operate the sensor in the best measurement state, the simple typical regulated power supply described in Figure 1-10 should be used.

(9) The sensor's magnetic saturation point and circuit saturation point make it have a strong overload capacity, but the overload capacity is time-limited. When the test overload capacity is exceeded, the overload current more than 2 times must not exceed 1 minute.

(10) The temperature of the primary side busbar must not exceed 85°C. This is determined by the characteristics of the ABS engineering plastics. The user has special requirements and can choose high temperature plastics as the shell.

Hall voltage sensors and Hall current sensors are mainly used for voltage and current measurement in industrial control fields. Since the sensor generally does not provide the index of angular difference, it is necessary to verify the angular difference indicator for occasions where it is necessary to accurately measure the AC power. This requires special attention. The power frequency measurement can be replaced by a transformer. The frequency measurement can be replaced by a combination of voltage and current frequency conversion power sensors.

9 applications

Hall sensor technology applied to the automotive industry

Hall 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 sensors are available in switch, analog and digital sensors.

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

The form of Hall sensor determines the difference of the amplifying circuit, and its output must adapt to the controlled device. This output may be analog, such as an accelerometer 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 as a throttle position sensor in a temperature meter or a power control system in an air conditioning system. The Hall element is connected to a differential amplifier and the amplifier is connected to an NPN transistor. The magnet is fixed on the rotating shaft. When the shaft rotates, the magnetic field on the Hall element is strengthened. The resulting Hall voltage is proportional to the strength of the magnetic field.

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

Hall sensor applied to taxi meter

Application of Hall sensor on taxi meter: The signal detected by Hall sensor A44E mounted on the wheel is sent to the SCM, processed and calculated, and sent to the display unit. This completes the mileage calculation. Detection principle, P3.2 port as the signal input, the internal use of external interrupt 0, each wheel of the wheel (set the wheel circumference is 1 m), Hall switch detects and outputs the signal, causing the microcontroller to interrupt, Pulse counting, when the count reaches 1000, that is, 1 km, the microcontroller will automatically increase the amount of control.

Whenever the Hall sensor outputs a low-level signal, the microcontroller will be interrupted once. When the odometer counter counts 1 000 times of the odometer pulse, the program will accumulate the current total and the microcomputer will enter the mileage counter interrupt service routine. In this program, you need to complete the cumulative operation of the current mileage and total amount and store the result in the mileage and total registers.

Application of Hall Current Sensor in Frequency Converter

A magnetic field is induced around a current flowing through the wire, and a magnetic field induced by the current is detected by a Hall device to measure the magnitude of the current that generates the magnetic field. As a result, Hall current and voltage sensors can be constructed. Since the output voltage of the Hall device is proportional to the product of the magnetic induction applied thereto and the operating current flowing therethrough, it is a device having a multiplier function and can be directly interfaced with various logic circuits and can also be directly driven. Various kinds of loads. 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, so it also plays a very important role in the frequency converter.

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

The Hall current sensor can be divided into direct measurement type and zero-flux type according to its operating mode. In the frequency converter, precise control and calculation are needed, so the zero-flux method is selected. The output voltage of the Hall device is amplified, and after current amplification, this current is passed through the compensation coil, and the magnetic field generated by the compensation coil and the magnetic field generated by the measured current are in opposite directions. If the condition IoN1=IsN2 is satisfied, the magnetic core is The magnetic flux in 0 is 0, then the following formula holds:

Io=Is(N2/N1)

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

The Hall current sensor is characterized by a "potentiometric" detection of the current. That is, the measurement circuit can realize current detection without having to connect the circuit under test, and they are coupled by a 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 circuit under inspection do not affect each other.