Application Cases

Experiment Name: Experimental Study of AC-DC Hybrid Strong Electric Field Sensors

Experiment Purpose: To build a test platform for testing the sensor's response under AC-DC hybrid electric fields, to separate and extract the target signal components in the modulated electric field, to measure the strength of AC-DC hybrid electric fields and determine the polarity of the DC electric field, to verify the effectiveness of the sensing method, and to calibrate the sensor.

Testing Equipment: High-voltage amplifier, function signal generator, oscilloscope, photodetector, laser source, etc.

Figure 1: Sensor Testing and Calibration Platform

Experiment Process:

The test platform for the AC-DC hybrid strong electric field sensor is built as shown in Figure 1. The function signal generator produces an AC (50Hz) and DC mixed voltage signal, which is amplified by the high-voltage amplifier and applied to the upper flat electrode. The lower flat electrode is grounded, creating a uniform electric field between the two electrodes. The rotating shielding electrode of the electric field modulation mechanism is placed close to the lower flat electrode and rotates at a constant speed driven by a motor, reliably grounded through a brush. A high-precision laser source emits a laser with a wavelength of 1550nm, which is transmitted through a single-mode fiber to the electro-optic sensing unit. Under the action of the modulated electric field, the intensity of the laser changes accordingly and is transmitted through a multi-mode fiber to the photodetector for intensity detection, achieving the measurement of the modulated electric field waveform. The monitoring signal of the high-voltage amplifier, the output signal of the photodetector, and the output signal of the optical encoder are measured and recorded by the oscilloscope.

The motor speed is set to 1000r/min, and the number of openings in the shielding electrode is 6, resulting in an electric field modulation frequency of 100Hz. DC electric fields and AC (50Hz) DC hybrid electric fields are applied between the upper and lower flat electrodes, respectively. Due to the modulation effect of the rotating shielding electrode, the photodetector outputs a changing voltage signal, as shown in Figure 2.

Figure 2: Measured Modulated Electric Field Waveform

When the applied electric field is a DC electric field, the output waveform of the photodetector is a sine wave with a period of 100Hz, the same as the modulation frequency. When the applied electric field is an AC-DC hybrid electric field, due to the presence of the AC electric field, different harmonic components appear in the output waveform of the photodetector after modulation. The above results show that the electric field modulation mechanism is effective, and the electric field under the rotating shielding electrode has changed accordingly after modulation. Keeping the DC (AC) electric field strength in the AC-DC hybrid electric field constant, the AC (DC) electric field strength is gradually increased, and the output waveform is recorded and subjected to Fourier analysis. As shown in the spectrum in Figure 3, when the DC electric field strength is kept constant at 100kV/m, the peak-to-peak value of the AC electric field strength is gradually increased to 225kV/m. The measured waveform spectrum mainly contains 50Hz, 100Hz, and 150Hz components, which are consistent with the analysis results. Among them, the 50Hz and 150Hz components are generated by the AC electric field, and their amplitudes represent the strength of the AC electric field; the 100Hz component is generated by the DC electric field and represents the strength of the DC electric field.

Figure 3: Spectrum Analysis of Measured Waveform

Experimental Results:

When the AC electric field strength increases, the amplitudes of the 50Hz and 150Hz components increase linearly, while the amplitude of the 100Hz component remains unchanged, with an error of only within 1%. Similarly, as shown in the spectrum in Figure 3(b), when the peak-to-peak value of the AC electric field strength is kept constant at 150kV/m and the DC electric field strength is gradually increased to 150kV/m, the amplitude of the 100Hz component in the measured waveform, which represents the strength of the DC electric field, increases linearly, while the amplitudes of the 50Hz and 150Hz signals representing the strength of the AC electric field remain unchanged, with a maximum error of no more than 2%. It can be seen that the electric field modulation mechanism has achieved the desired modulation effect. The external AC or DC electric field strength only affects its corresponding frequency components, and the theoretical analysis is consistent with the experimental results.

Voltage Amplifier Recommendation: ATA-7020

Figure: Specification Parameters of the ATA-7020 High-Voltage Amplifier

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