The principle of the new Hall sensor and the Hall effect

The principle of the new Hall sensor and the Hall effect

The Hall sensor is a magnetic field sensor fabricated according to the Hall effect. The Hall effect is a kind of magnetoelectric effect, which was discovered by Hall (AHHall, 1855-1938) in 1879 when studying 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 that of metals. Various Hall elements made by this phenomenon are widely used in industrial automation technology, detection technology, information processing, etc. aspect. The Hall effect is the basic method for studying the properties of semiconductor materials. The Hall coefficient measured by the Hall effect experiment can determine important parameters such as conductivity type, carrier concentration, and carrier mobility of the semiconductor material.

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

principle

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

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

Hall Effect

A Hall element typically has four terminals, two of which are the input of the bias current I of the Hall element and the other two are the output of the Hall voltage. If the two outputs form an outer loop, a Hall current is generated. In general, the setting of the bias current is usually given by an external reference; if the accuracy is high, the reference is replaced by a constant current source. In order to achieve high sensitivity, some Hall elements are coated with a coating alloy with high magnetic permeability; the Hall potential of these sensors is large, but saturation occurs at around 0.05T, which is only applicable to low-quantity limits. Used in small scales.

A control current I is applied across the semiconductor wafer, and a uniform magnetic field having a magnetic induction B of B is applied in the vertical direction of the sheet, and a Hall voltage having a potential difference of UH is generated in a direction perpendicular to the current and the magnetic field.

working principle

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

The Hall voltage changes with the change of the magnetic field strength. The stronger the magnetic field, the higher the voltage, the weaker the magnetic field, the lower the voltage, the smaller the Hall voltage, 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 the Hall IC is used for sensing, a mechanical method is required to change the magnetic induction. The method shown in the figure below uses a rotating impeller as a switch to control the magnetic flux. When the impeller blades are in the air gap between the magnet and the Hall integrated circuit, the magnetic field deviates from the integrated piece and the Hall voltage disappears. Thus, the change of the output voltage of the Hall integrated circuit can indicate a certain position of the impeller drive shaft. With this working principle, the Hall IC can be used as the ignition timing sensor. The Hall effect sensor is a passive sensor that requires an external power supply to operate. This feature allows it to detect low speed operation.

classification

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

(1) The switching Hall sensor consists of a voltage regulator, a Hall element, a differential amplifier, a Schmitt trigger and an output stage, which outputs a digital quantity. The switch type Hall sensor also has a special form called a lock type Hall sensor.

(B) The linear Hall sensor consists of a Hall element, a linear amplifier, and an emitter follower, which outputs an analog quantity.

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

Switch type

Among them, Bnp is the magnetic induction intensity of the operating point "on", and BRP is the magnetic induction intensity of the release point "off". When the applied magnetic induction exceeds the operating point Bnp, the sensor outputs a low level. When the magnetic induction decreases below the operating point Bnp, the sensor output level does not change, and the sensor is lowered to the release point BRP. Jump to high level. The hysteresis between Bnp and BRP makes the switching action more reliable.

Lock type

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

Closed loop current sensor

The magnetic balance type current sensor is also called a Hall closed-loop current sensor, also called a compensation type sensor, that is, the magnetic field generated by the main circuit measured current Ip at the collecting magnetic ring is compensated by a magnetic field generated by the current through a secondary coil, thereby The Hall device is in an active state of detecting zero flux.

The specific working process of the magnetic balance current sensor is: when a current flows through the main circuit, the magnetic field generated on the wire is concentrated by the collecting ring and sensed on the Hall device, and the generated signal output is used to drive the corresponding power tube and Turn it on to obtain a compensation current Is. This current then generates a magnetic field through a multi-turn winding that is exactly opposite to the magnetic field produced by the current being measured, thereby 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. At this time, the Hall device functions to indicate zero flux, which 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 unbalanced magnetic field. From the imbalance of the magnetic field to the rebalancing, the time required is theoretically less than 1 μs, which is a process of dynamic equilibrium.

use

Hall devices have many advantages. They are solid in structure, small in size, light in weight, long in life, easy to install, low in power consumption, high in frequency (up to 1 MHZ), resistant to vibration, and not afraid of dust, oil, water vapor and salt spray. Contaminated or corroded.

The Hall linear device has high precision and good linearity; the Hall switch device has no contact, no wear, clear output waveform, no jitter, no rebound, and high position repeatability (up to μm level). 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 objects being detected, their applications can be divided into direct applications and indirect applications. The former directly detects the magnetic field or magnetic characteristics of the object to be detected, and the latter detects the artificially set magnetic field on the object to be used, and uses this magnetic field as a carrier for the detected information, through which many non-electrical and non-magnetic materials are used. Physical quantities such as force, moment, pressure, stress, position, displacement, velocity, acceleration, angle, angular velocity, number of revolutions, rotational speed, and time at which the operating state changes are converted into electrical quantities for detection and control.

application

Hall sensor technology for 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 switching, analog and digital sensors.

Hall sensors can be made of metals and semiconductors. The quality of the effect depends 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 the Hall sensor determines the difference in the amplifying circuit and its output is adapted to the device being controlled. This output may be analog, such as an acceleration position sensor or a throttle position sensor, or it may be digital. Such as crankshaft or camshaft position sensor.

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

When a 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 Schmitt trigger. In this configuration. The sensor outputs an on or off signal. In most automotive circuits, the Hall sensor is a current sink or grounds the signal circuit. To do this, an NPN transistor is required to connect to the output of the Schmitt trigger. The magnetic field passes through the Hall element and the blades on one of the trigger wheels pass between the magnetic field and the Hall element.

Hall sensor applied to taxi meter

The application of the Hall sensor on the taxi meter: the signal detected by the Hall sensor A44E mounted on the wheel is sent to the single chip microcomputer, processed and calculated, and sent to the display unit, thus completing the mileage calculation. The detection principle, P3.2 port as the input end of the signal, the internal use of external interrupt 0, each turn of the wheel (set the circumference of the wheel is 1 m), the Hall switch detects and outputs the signal, causing the interrupt of the microcontroller, Pulse counting, when the count reaches 1 000 times, that is, 1 km, the microcontroller will automatically increase the amount.

Whenever the Hall sensor outputs a low level signal, the MCU interrupts once. When the mileage counter counts the mileage pulse for 1 000 times, the program accumulates the current total amount, so that the microcomputer enters the mileage count interrupt service routine. In this program, the accumulation of the current mileage and total amount needs to be completed, and the result is stored in the mileage and total registers.

Application of Hall current sensor in frequency converter

A magnetic field is induced around a wire through which a current flows, and a Hall device is used to detect the magnetic field induced by the current, and the magnitude of the current generating the magnetic field can be measured. Thus, a Hall current and a voltage sensor 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 operating current flowing through it, it is a device with multiplier function, and can directly interface with various logic circuits, and can also be directly driven. Loads of various natures. 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. Since the response time of the Hall current sensor is shorter than 1μs, when an overload short circuit occurs, the power supply can be cut off before the transistor reaches the limit temperature, so that the transistor can be reliably protected.

Hall current sensors can be divided into direct measurement type and zero magnetic formula according to their working modes. Because of the need for precise control and calculation in the inverter, the zero flux mode is selected. Amplify the output voltage of the Hall device, and then, after current amplification, let the current pass through the compensation coil, and the magnetic field generated by the compensation coil and the magnetic field generated by the measured current are opposite. If the condition IoN1=IsN2 is satisfied, the magnetic core The magnetic flux in is 0, then the following formula holds:

Io=Is(N2/N1)

Where, Io is the current to be measured, that is, the current in the primary winding in the 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. It can be seen from the above formula that when the magnetic balance is reached, Io can be obtained from Is and the turns ratio N2/N1.

Hall current sensors are characterized by "potential-free" detection of current. That is, the measurement circuit can realize current detection without having to access 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 to be inspected do not affect each other.

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