Current sensors, also known as magnetic sensors, can be used in household appliances, smart grids, electric vehicles, wind power, and so on. Many magnetic sensors are used in our daily lives, such as computer hard drives, compasses, household appliances, and so on.

A closed-loop Hall current sensor is a product that uses Hall devices as the core sensitive element for isolating and detecting current. Its working principle is Hall magnetic balance (also known as Hall magnetic compensation or Hall zero flux). As is well known, when current flows through a straight wire, a magnetic field is generated around the wire, and the magnitude of the magnetic field is proportional to the magnitude of the current flowing through the wire. This magnetic field can be concentrated by soft magnetic materials and then detected by Hall devices. Due to the good linear relationship between the change in magnetic field and the output voltage signal of the Hall device, the measured output signal of the Hall device can be used to directly reflect the magnitude of the current in the wire, that is:

I ∝ B ∝ VH (2)

In the formula: I is the current passing through the wire; B is the magnetic induction intensity generated by the current passing through the wire; VH is the Hall voltage generated by the Hall device in magnetic field B. When selecting appropriate proportional coefficients, the above relationship can be expressed as an equation. For the processing of Hall output voltage signal VH, many circuits have been designed, but overall they can be divided into two categories: open-loop (or direct measurement, direct detection) Hall current sensors; The other type is a closed-loop (or zero flux, magnetic balance) Hall current sensor.

For the circuit form of Hall sensors, the most common idea is to directly amplify the output voltage of the Hall element to obtain the required signal voltage, and use this voltage value to calibrate the measured current on the primary side. This type of Hall sensor is usually called an open-loop Hall current sensor. The advantages of open-loop Hall sensors are simple circuit form and relatively low cost; Its disadvantage is poor accuracy and linearity; Slow response time; The temperature drift is significant. In order to overcome the shortcomings of open-loop sensors, closed-loop Hall current sensors appeared abroad in the late 1980s. In 1989, Beijing 701 Factory introduced foreign technology and was the first in China to develop and produce closed-loop Hall current sensors. After more than a decade of effort, this type of sensor has gradually been understood and applied by a large number of users in China.

The working principle of a closed-loop Hall current sensor is magnetic balance, which means that the magnetic field generated by the primary current (IN) is compensated by the magnetic field generated by the current (IM) of a secondary coil, so that the Hall device is always in a state of detecting zero magnetic flux. When the magnetic field generated by the compensating current of the primary and secondary sides reaches equilibrium in the middle, there is the following equation:

N × IN=n × IM (3)

In the formula: IN is the primary current; N is the number of turns of the primary coil; IM is the secondary compensation current; N is the number of turns of the secondary coil.

From the above equation, it can be seen that when the primary and secondary coil turns of the sensor are known

When counting, the value of the primary current IN can be calculated by compensating for the magnitude of the secondary current IM, thus achieving isolated measurement of the primary current.

Below are the precautions for using current sensors.

In the field of industrial applications, the most popular type of magnetic sensor is the current sensor. In many applications that measure currents below 50 amperes, such as residential solar applications or small UPS systems, simple resisve bars or shunts are used

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

2. When a large DC current flows through the primary coil of the sensor during use, and the secondary circuit is not connected to the power supply | voltage regulator or the secondary side is open circuited, the magnetic circuit is magnetized, resulting in residual magnetism and affecting measurement accuracy (therefore, the power supply and measurement terminal M should be connected first). When this situation occurs, demagnetization treatment should be carried out first. The method is to not apply power to the secondary circuit, but to pass the same level of AC current through the primary coil and gradually reduce its value;

3. In most cases, Hall sensors have strong resistance to external magnetic field interference. Generally, the magnetic field interference generated by a current twice the working current Ip between 5-10cm from the module can be ignored. However, when there is stronger magnetic field interference, appropriate measures should be taken to solve it. The usual methods are:

① Adjust the module direction to minimize the impact of external magnetic fields on the module;

② Add a magnetic field resistant metal shielding cover on the module;

③ Select modules with dual or multiple Hall elements;

④ The best accuracy of measurement is obtained at the rated value. To achieve the best accuracy when the measured current is far below the rated value, multiple turns can be used on the primary side, that is, IpNp=rated ampere turns. In addition, the temperature of the primary feeder should not exceed 80 ℃.

Hall Current Sensor Due to its numerous advantages, precise detection and control of high currents ensure the safe and reliable operation of frequency converter products, enabling them to handle abnormal situations in a timely manner while outputting normally. Improved the reliability and safety quality of the frequency converter. So the advantages of Hall current sensors in frequency converters are becoming increasingly apparent and have become an indispensable part of the frequency converter industry.