Hall current sensor can measure various types of current, from direct current to alternating current of tens of kilohertz. Its working principle is mainly based on the principle of the Hall effect.
When the primary wire passes through the current sensor, the primary current IP will generate magnetic lines of force. The magnetic field lines of the primary side are concentrated around the air gap of the magnetic core. The Hall electrode built in the air gap of the magnetic core can generate an induced voltage proportional to the magnetic field lines of the primary side, whose magnitude is only a few millivolts. The tiny signal is transformed into the secondary current IS and there is the following relationship: IS* NS= IP*NP.
Among them, IS—secondary side current; IP—primary side current; NP—primary side coil turns; NS—secondary side coil turns; NP/NS—turns ratio, generally take NP=1.
1. The output signal of the Hall effect current transducer
The secondary current IS is proportional to the input signal (primary current IP). IS is generally very small, which is only 10~400mA. If the output current passes through the measuring resistor RM, a voltage output signal of several volts proportional to the primary current can be obtained.
2. Sensor supply voltage VA
VA refers to the supply voltage of the current sensor, which must be within the range specified by the sensor. Beyond this range, the sensor will not work properly or its reliability will be reduced. In addition, the power supply voltage VA of the sensor is further divided into a positive power supply voltage VA+ and a negative power supply voltage VA-. Pay attention to the single-phase power supply sensor. Its power supply voltage VAmin is twice the two-phase power supply voltage VAmin, so its measurement range is correspondingly higher than that of the dual-phase power supply sensor.
3. Measuring range Ipmax
The measurement range refers to the maximum current value that the current sensor can measure. The measurement range is generally higher than the standard rated value IPN.
1. Standard rating IPN and rated output current ISN
IPN refers to the standard rated value that the current sensor can test, which is expressed in RMS (A, r, m, s). The size of the IPN is related to the model of the sensor product. ISN refers to the rated output current of the current sensor, which is generally 10~400mA. Of course, it may vary according to some models.
2. Offset current ISO
The offset current is also called residual current or residual current, which is mainly caused by the unstable working state of the Hall element or the operational amplifier in the electronic circuit. When the current sensor is in production, at 25°C and IP=0, the offset current has been adjusted to the minimum. But when the sensor leaves the production line, a certain amount of offset current will be generated. The accuracy mentioned in the product technical documentation takes into account the effect of increased offset current.
Linearity determines the degree to which the sensor output signal (secondary current IS) is proportional to the input signal (primary current IP) within the measurement range.
4. Temperature drift
The offset current ISO is calculated at 25°C. When the ambient temperature around the Hall electrode changes, the ISO will change. Therefore, it is important to consider the maximum change in offset current ISO, where IOT refers to the temperature drift value in the current sensor performance table.
The overload capability of the Hall current sensor means that when current overload occurs, outside the measurement range, the primary current will still increase, the duration of the overload current may be very short and the overload value may exceed the allowable value of the sensor. The overload current value sensor generally cannot measure it, but it will not cause damage to the sensor.
The accuracy of Hall effect current transducer depends on the standard current rating, IPN. At +25°C, the measurement accuracy of the sensor has a certain influence on the primary current. At the same time, the influence of offset current, linearity, and temperature drift must also be considered when evaluating the accuracy of the sensor.
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