When using the power analyzer to measure data, choose the appropriate synchronization source. If the synchronization source is set incorrectly, the measured value may be unstable or error. The harmonic measurement mode also selects the appropriate PLL source. Many customers often ask questions. What are the similarities and differences between the sync source and the PLL source, and what is their role? In order to accurately calculate the measured values ​​such as power, it is necessary to intercept the data from the sampled data according to the complete signal period. The original sampled signal has two kinds of voltage and current. Since the signal period of the voltage and current cannot be exactly the same, no matter the choice The voltage signal period is used as the interception basis, or the current signal period is selected as the interception basis. It is impossible to intercept the complete signal period perfectly. What should I do? Selecting a signal with small distortion, input level and frequency from the voltage and current as the interception basis, such a signal is easy to measure the signal period, and thus the calculated power and other measured values ​​are certainly relatively good, then the interception basis The signal is called the synchronization source. From this, the basis for selecting the synchronization source can be obtained, that is, the input signal with small distortion and stable frequency is selected as the synchronization source. When the measured object is a frequency converter, the distortion of the current waveform is smaller than the voltage waveform, please select the current signal as the synchronization source. In the power analyzer PA6000, the normal measurement mode only needs to set the synchronization source. It is not necessary to set the PLL source. It is only necessary to set the PLL source in the harmonic mode and IEC harmonic mode. Why introduce a PLL source when measuring harmonics? The core of harmonic measurement is the time domain to frequency domain conversion. Discrete Fourier Transform (DFT) is a time domain to frequency domain conversion of digital signals. The efficient DFT method is Fast Fourier Transform (FFT), which uses FFT to implement harmonic measurements. There is a hypothesis in the FFT algorithm that assumes that discrete time series can be cyclically extended throughout the time domain. All signals containing the discrete time series are periodic functions, and the period is related to the length of the time series. However, if the length of the time series is not an integer multiple of the signal period, a spectral leak will occur if the condition is not true. When performing FFT analysis on a signal, if the sampling frequency is fixed, due to the small change of the frequency of the sampled signal and the influence of the interference factor, the collected data is not an integer multiple of the signal period, and a spectrum leak occurs at this time. The PLL phase-locked loop is a feedback circuit that synchronizes the phase of the clock on the circuit with the phase of an external clock. The PLL synchronizes by comparing the phase of the external signal with the phase of the voltage controlled crystal oscillator (VCXO). During the comparison, the phase-locked loop circuit continuously adjusts the clock phase of the local crystal according to the phase of the external signal until two The phase of the signal is synchronized. By introducing PLL hardware, the PA6000 synchronizes the sampling frequency with the signal frequency, and then maintains the sampling frequency by an integral multiple of the signal frequency by multiplying, ensuring that the acquired data is exactly an integer multiple of the signal period, thereby eliminating spectral leakage. How to choose the PLL source, the principle of selecting the synchronization source can be known, of course, choose the input signal with small distortion and stable frequency as the PLL source! Compared to the PA6000, Zhou Ligong Zhiyuan Electronics' latest PA5000 power analysis already supports dual PLL sources. Users can select different PLL sources for different measurement channels. Figure 1 Setting the PLL source Figure 2 Setting the PLL source used by the measurement channel 24V Frequency Transformer,110V 60Hz To 220V 50Hz Transformer,Oil-Filled Electric Transformer, electronic oiled transformer IHUA INDUSTRIES CO.,LTD. , https://www.ihua-sensor.com
