Closed-loop Hall current sensor works - Database & Sql Blog Articles

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The closed-loop Hall current sensor is a modular product that uses the Hall device as the core sensitive component to isolate the detection current. Its working principle is Hall magnetic balance type (or Hall magnetic compensation type, Hall zero magnetic type). ). It is well known that when a current flows through a straight wire, a magnetic field is generated around the wire. The magnitude of the magnetic field is proportional to the amount of current flowing through the wire. This magnetic field can be concentrated by a soft magnetic material and then detected by a Hall device. Since the change of the magnetic field has a good linear relationship with the output voltage signal of the Hall device, the measured output signal of the Hall device can directly reflect the current in the wire, that is:

I∝B∝VH(2)

Where: I is the current through the wire; B is the magnetic induction generated after the wire is passed through; VH is the Hall voltage generated by the Hall device in the magnetic field B. When an appropriate scale factor is selected, the above relationship can be expressed as an equation. For the processing of the Hall output voltage signal VH, many kinds of circuits have been designed, but generally can be divided into two categories, one is open-loop (or direct-measurement, direct-check) Hall current sensor; the other The class is a closed loop (or zero magnetic, magnetic balance) Hall current sensor.

For the circuit form of the Hall sensor, the most easily thought is to directly amplify the output voltage of the Hall element with an operational amplifier to obtain the required signal voltage, thereby calibrating the current measured by the voltage value. This form of Hall sensor is commonly referred to as an open loop Hall current sensor. The advantage of the open-loop Hall sensor is that the circuit form is simple and the cost is relatively low; its disadvantages are poor accuracy and linearity; slow response time; and large temperature drift. In order to overcome the shortcomings of the open-loop sensor, a closed-loop Hall current sensor appeared in foreign countries in the late 1980s. In 1989, the introduction of foreign technology in Beijing Qiyi Factory took the lead in the development and production of closed-loop Hall current sensors in China. After more than ten years of hard work, this kind of sensor has gradually been understood and applied by users in China.

The working principle of the closed-loop Hall current sensor is magnetically balanced, that is, 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 the detection. The working state of zero flux. When the magnetic field generated by the primary secondary compensation current reaches equilibrium in the core, the following equation is obtained:

N×IN=n×IM(3)

Where: 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.

It can be seen from the above equation that when the primary and secondary coil turns of the sensor are known, by measuring the magnitude of the secondary compensation current IM, the value of the primary current IN can be derived, thereby achieving the isolation measurement of the primary current. .