Application Cases

Experiment Name: Current Sensor Output Testing

Research Direction: Electromagnetic Testing

Test Objective:
To overcome the influence of temperature and spatial geomagnetic fields during measurement and to improve the measurement accuracy of the TMR current sensor, this study also investigates the output correction of the TMR current sensor under environmental interference. First, for abnormal output data caused by strong magnetic field interference or faults in the TMR current sensor, Bayesian theory combined with information entropy is used to identify and eliminate outliers. Second, the Adam algorithm is employed to optimize the fine-tuning process of the deep belief network, reconstructing the mapping relationship between the spatial geomagnetic field, temperature, and the TMR current sensor's measured output. Finally, calibration experiments and error analysis were conducted on the designed TMR current sensor. The experimental results show that within the temperature variation range of -40°C to 80°C, the sensitivity of the TMR current sensor to temperature and the spatial geomagnetic field is significantly reduced. Furthermore, by comparing the errors after data processing using four different algorithms, the superiority of the proposed algorithm in improving the output accuracy of the TMR current sensor is verified, demonstrating its ability to meet the measurement demands of smart grids well.

Testing Equipment: ATA-4012B high-voltage power amplifier, signal generator, current sensor, oscilloscope.

Experimental Procedure:

Figure: TMR Current Sensor and Physical Packaging

The main characteristics of the designed TMR current sensor, including static characteristics and frequency response characteristics, were tested. Using a TMR current sensor test platform at a room temperature of 25°C, the TMR current sensor was tested and analyzed.

Before using the TMR current sensor, it must be calibrated. The TMR current sensor output correction platform was used to test its static characteristics. A 125TCF constant temperature chamber was used to set the operating environment of the TMR current sensor to a room temperature of 25°C. DC input-output characteristic tests were performed on the designed TMR current sensor. A high-precision current source provided the measured DC current from 0 to 10 A with a step size of 0.05 A. The current was gradually increased from 0 A to 10 A, and the voltage output of the TMR current sensor was recorded. The input-output curve of the TMR current sensor is shown in Figure (a) below, and the calculated absolute output error is shown in Figure (b) below.

Figure: Input-Output Fitting Curve and Absolute Output Error

A constant temperature chamber was used to set the operating environment of the TMR current sensor to a room temperature of 25°C. The power supply current source for the Helmholtz coil was disconnected to maintain a clean test environment. Because the frequency of the current that the current source can generate is limited, a signal generator combined with the ATA-4012 power amplifier was used to perform frequency response testing on the closed-loop TMR current sensor. The output of the TMR current sensor was connected to channel A of a dual-channel oscilloscope, while the input signal was simultaneously connected to the other channel (channel B) of the oscilloscope. Keeping the amplitude of the measured current constant, its frequency was varied, and the phase difference between the input and output signals of the closed-loop TMR current sensor was observed. For the TMR current sensor measurement, the current was set to 0.2 A. The resulting frequency response characteristics of the closed-loop TMR current sensor at different frequencies are shown in the figure below.

Figure: Frequency Response Characteristics of the Closed-Loop TMR Current Sensor

From the figure above, it can be seen that the closed-loop TMR current sensor exhibits essentially no significant amplitude attenuation or phase delay in the range from DC to 100 kHz. In the range from 50 kHz to 1 MHz, its amplitude gradually attenuates, and the degree of phase delay gradually increases. When the frequency is 500 kHz, the output voltage of the closed-loop TMR current sensor is attenuated by -3 dB, and the output voltage phase lags by 14° at this frequency. Therefore, the -3 dB bandwidth of the closed-loop TMR current sensor can reach 500 kHz.

Experimental Results:
The test results show that the sensitivity of the designed closed-loop TMR current sensor reaches 200.03 mV/A, the linearity is 0.2%, and the bandwidth is 500 kHz. Furthermore, through calibration experiments and measurement error analysis of the TMR current sensor, the experimental results indicate that the proposed algorithm significantly reduces the sensitivity of the TMR current sensor's output data to temperature and the spatial geomagnetic field.

Figure: Specifications of the ATA-4012C High-Voltage Power Amplifier