Abstract
We present a method of calibration and error correction of the AMR yokeless current transducer consisting of a circular array of eight anisotropic magnetoresistors (AMR) with one feedback compensation loop. The main sources of errors are the nonidentical parameters of AMR sensors and off-center position of the measured current. It is well known that AMR sensors from the same batch have 2% spread of the sensitivity; we found that the variation of the factor of the internal compensation coil is the same. We developed a novel calibration process using the readings of individual residual uncompensated voltages of the AMRs. The position of the current inside the measurement hole is estimated from the individual voltages considering the influence of external DC magnetic field such as the Earth’s field. During the calibration phase, the sensor outputs are measured for several positions of the current conductor inside the measuring hole. As a result of calibration the lookup table of error corrections is calculated and stored in the memory, and then these values are used for the correction during the measurement of the unknown current. This procedure reduces the off-center error from 0.4% to 0.06%.
Highlights
Contactless DC/AC electric current transducers usually have magnetic circuit or yoke
In our previous paper [16] we introduced the methods how to improve the accuracy of the yokeless current transducer (Figure 1) with a circular array of anisotropic magnetoresistors (AMR)
Compensation current flows through planar compensation coils integrated on AMR sensor
Summary
Contactless DC/AC electric current transducers usually have magnetic circuit or yoke. The circular sensor array improves the resistance against the position of the measured conductor [9] and against the external magnetic field and current in external conductors [10]. Both errors decrease with increasing number of sensors, and eight sensors are considered as an optimum number. Compensation current flows through planar compensation coils integrated on AMR sensor All these coils are connected in series (see Figure 1). The sensitivity S influences the accuracy of current transducer only in the case the measured magnetic field is not well compensated by the compensation coil. We show that errors mentioned above can be suppressed by the reading of individual outputs of AMR sensors and digital processing of that data
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