Analysis of Hall Sensor

I. Introduction

Hall current sensor, Hall voltage sensor is the most widely used sensor device measurement, because it has high precision, good isolation, linearity number, fast response, frequency bandwidth, strong overload capability, etc., it is widely used. Frequency control devices, inverter devices, UPS power supplies, inverter welding machines, electrolytic plating, CNC machine tools, computer monitoring systems, power grid monitoring systems and high current and voltage fields that require isolation. In the case of high-voltage, high-current power electronics, accurate detection and control are also guaranteed.

Second, Hall sensor composition and principle

Hall current, voltage sensor is made according to Hall principle. It has two modes, magnetic balance and direct measurement. The Hall current, voltage sensor device is composed of a primary circuit, a Hall device, a secondary coil, a collecting ring, and an amplifying circuit.

2.1 Hall sensor Hall effect

The Hall effect refers to a physical phenomenon in which a lateral potential difference occurs when a magnetic field acts on a carrier metal conductor or a carrier in a semiconductor. The Hall Metal effect was discovered by American physicist Hall in 1879. When passing through the metal foil, when the magnetic field is applied perpendicularly to the direction of the current, a lateral potential difference occurs on both sides of the metal foil.

The Lorentz force and electric field force balance are listed as Bvq = U / L·q (B is the strength of magnetic induction, v is the speed of free electrons, q is the amount of free electron charge, Hall voltage U, l is the length of the cross section) , so that U = Bv, which depends on the microscopic current I = nevs, then the interpretation of v = I / (nes), with U = Bv, get U = BI / (ned) (the thickness of the Hall element d), such as Let K = 1 /(ne), then U = kIB / d, K is the Hall coefficient.

The Hall element can convert the magnetic quantity of magnetic induction into the electrical quantity of voltage.

Voltage and current sensors fabricated using Hall effect are highly accurate and are an effective tool for electrical measurements.

The current in the wire is proportional to the magnetic field around it. It is possible to use a Hall element to measure the magnetic field, thereby determining the current in the wire. The Hall current sensor is thus designed. It is characterized by being isolated from the circuit under test and does not affect the circuit under test, especially for high current detection.

In the magnetic balance Hall current sensor, the Hall device detects the Hall voltage signal through the magnetic flux generated by the aggregation of the primary current Ip in the magnetic circuit, and the voltage signal accurately reflects the original primary current after being amplified by the amplifier. The magnetic flux generated by the primary current Ip is balanced with the secondary current Is generated by the amplification of the Hall voltage by the magnetic flux generated by the secondary coil. The secondary current Is accurately reflects the primary current.

The magnetic balance Hall voltage sensor primary voltage Vp is converted into a primary current Ip by a primary resistor R1, and the magnetic flux generated by Ip is balanced with the magnetic flux generated by the secondary coil by the secondary current Is generated by the amplification of the Hall voltage. The secondary current Is accurately reflects the primary voltage.

When the Hall element is placed in the electromagnetic field of the electric field strength E and the magnetic field strength H, the current I generated in the element and the potential difference are proportional to the intensity electric field E. If the electromagnetic field, the value of the instantaneous power density P determined by P = EH is P = EH is determined. This method can constitute a Hall power sensor

 If the switch integrated with the Hall element is regularly arranged on the object at a predetermined position, when it is mounted through the permanent magnet, the pulse signal can be obtained from the measurement of the measuring circuit. The pulse signal is capable of detecting the moving speed of the moving object. If the number of measurements of pulses transmitted per unit time is determined, the speed of movement can be determined.

2.2 current sensor

Hall current sensors can measure various types of current, from DC to tens of kilohertz of AC, based on the principle of Hall effect.

When the primary current conductor passes through the current sensor, a primary current IP generates magnetic lines of force, which are concentrated around the core air gap, and the Hall piece built into the air gap of the core can be generated proportional to the primary magnetic line, and the size is only For a few millivolts of induced voltage, this tiny signal can be converted into a secondary current IS by a subsequent electronic circuit, and the following relationship exists: IS* NS= IP*NP

Where IS- secondary current;

IP-primary current;

One turn NP;

NS-secondary coil turns;

NP / NS - reports rotation, usually NP = 1.

 The output signal of the current sensor is the secondary current IS, which is proportional to the input signal (primary current IP), which is generally low, only 10-400 mA. If the current is output through the measuring resistor RM, an output signal voltage of a few volts proportional to the primary current can be obtained.

2.3 magnetic balance current sensor (closed loop series CST)

The magnetic balance type current sensor is 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 the magnetic field generated by a secondary coil current, so that the Hall device is in detecting the zero magnetic flux. Working status.

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. Turn it on to obtain a compensation current Is. This current then generates a magnetic field through the multi-turn winding, which is exactly opposite to the magnetic field generated by the current being measured, thus compensating for the original magnetic field, causing the output of the Hall device to gradually decrease. 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, and Ip can be tracked by Is at this time. When the Ip changes, the balance is destroyed, and the Hall device has a signal output, that is, the above process is repeated, and finally the balance is reached again. 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.

2.4 Hall Voltage Sensor (closed loop HNV series)

 The Hall voltage sensor works like a closed-loop current sensor and works in a magnetically balanced manner. According to the Hall effect, a Hall element is made of a semiconductor material, which has the advantages of being sensitive to a magnetic field, simple structure, small volume, wide frequency response, large output voltage variation, and long service life, and thus, in measurement, automation, computer and Information technology and other fields are widely used.

Third, the performance characteristics

 Hall current and voltage sensors have superior electrical performance and are an advanced electrical detection component that isolates the main circuit and electronic control circuitry. It combines all the advantages of transformers and shunts while overcoming the deficiencies of transformers and shunts (the transformers are only suitable for 50Hz power frequency measurements; the shunts are not capable of isolated measurements). The same Hall current and voltage sensor can detect both AC and DC, and even detect transient peaks, making it a new generation of alternative transformers and shunts. Hall current and voltage sensors have the following characteristics:

It can measure the voltage and current of arbitrary waveforms. Hall voltage and current sensors measure current and voltage parameters of arbitrary waveforms such as DC, AC, and pulse waveforms. Transient peak parameters can also be measured, and the secondary circuit can faithfully reflect the waveform of the primary current. This ordinary transformer can not be compared with it, because ordinary transformers are generally only suitable for 50Hz sine waves;

High precision. The general Hall current and voltage sensor has an accuracy of better than 1% in the working area. This precision is suitable for any waveform measurement, while the general transformer accuracy is generally 3% to 5%, and is only suitable for a 50Hz sinusoidal waveform;

The general linearity is better than 0.5%, which can fully meet the requirements for general industrial control. Good dynamic performance; working frequency bandwidth; strong overload capability; large measuring range; high reliability, average trouble-free operation greater than 5 × 10000 hours; small size, light weight, easy to install and will not bring any loss to the system.

Fourth, the connection method of the Hall sensor

The current and voltage sensors need only external positive and negative DC power supply. The measured current busbar is generally passed through the sensor or connected to the primary terminal, and then the simple connection at the secondary end can complete the isolation detection of the main control circuit. The design is very simple. When used with the transmitter, it can be easily interfaced with a computer or various instruments after A/D conversion, and can be transmitted over long distances.

4.1 Magnetic balance (compensation) wiring method

The magnetic balance (compensation) type current and voltage sensor/converter has two series of HNC and HNV: the output signal is mostly current. (If the voltage output mode is required, the sampling resistor can be externally connected between the M terminal and the current ground according to the required voltage level or the necessary voltage can be amplified by the sampling voltage.) The three terminals of the conventional sensor are: positive power input Connected to the "+" terminal, the negative power input is connected to the "-" terminal, and the "M" terminal is the signal output terminal.

4.2 Direct wiring method

The direct current sensor has the HDC series. Its output signal is voltage mode. Under the rated working condition, its standard output signal is ±4V, which can be selected by users. There are zero points and gain potentiometers on the sensor, so users do not need to make adjustments. If the user has special requirements, it can be customized to the factory. The wiring method of the direct current type sensor may vary depending on the specific product, but most of the four terminal blocks are: positive power input connected to "+" end, negative power input connected to "-" end, "M" The terminal is the signal output terminal, and the "0" terminal is the power supply ground.

4.3 Voltage sensor wiring method

The voltage sensor generally has five terminals, of which “V +” and “V-” are primary terminals, which are respectively connected to the positive and negative terminals of the voltage input terminal to be tested. The other three terminals are secondary terminals, the "+" terminal is connected to the +15V power supply, the "-" terminal is connected to the -15V power supply, and the "M" terminal is the signal output terminal.

 According to the difference of the measured voltage, the user can connect a current limiting resistor R to one end of the measured voltage and then connect it to the sensor. The size of the series resistor R is determined by the following formula:

R=Vp/Iin-Rin

Where R is the series resistance, Vp is the measured voltage, Iin is the rated input current, and Rin is the primary internal resistance of the sensor.

The power of the series resistor is determined by W=Vp·Iin

5. When using Hall sensors, the following points should be noted:

(1) When using the sensor, turn on the secondary power supply first, and then turn on the current or voltage once.

(2) When measuring current, it is best to fill the module aperture with a single wire to get the best dynamic characteristics and sensitivity.

(3) When measuring the voltage, the measured voltage should be connected in series with the current limiting resistor. After obtaining the primary current specified by the sensor, connect the voltage sensor to the primary terminal.

(4) The accuracy of the Hall effect sensor depends on the standard rated current IPN. At +25 °C, the measurement accuracy of the sensor has a certain influence on the primary current. At the same time, the offset current must be considered when assessing the accuracy of the sensor. When the measured current is lower than the rated value, in order to obtain better accuracy, more than one can be used at a time. , ie: Ip*Np=rated ampere-turns.

(5) Overload condition, the overload capability of the current sensor means that when the current overload occurs, the current will increase outside the measurement range, and the duration of the overload current may be short, and the overload value may exceed the allowable value of the sensor. The overload current value sensor is generally not measured, but will not cause damage to the sensor.

(6) Temperature drift, Hall power sensor generally has temperature drift, offset current ISO is calculated at 25 ° C, when the ambient temperature of the Hall electrode changes, ISO will change. Therefore, in practical applications, it is important to consider the maximum variation of the offset current ISO. Temperature drift can be compensated for in subsequent signal processing.