This thesis describes the development of a line impedance meter, for the power line communications frequency range, based on the Red Pitaya STEMlab 125--14 development board.
First, the existing research in the field is presented, showing different measurement methods and practical meter implementations. The design process, which takes into account the properties of the development board, is described. The meter uses a short frequency sweep, which is injected into the power line, while capturing the current and voltage signals. The impedance spectrum is calculated using the FFT algorithm and complex division. The meter supports measuring the impedance with an adjustable frequency over a longer time period.
The circuit was tested using circuits with known impedance frequency characteristics. The results show a good match between the measured and actual characteristics, confirming correct functionality. Measurement of the line's transfer function using the same circuit was also tested using filters with known transfer functions. The results don't match as well, but the error can be explained.
Finally, the circuit was also tested on the real power line. The results show the effects of nearby switching power supplies, the difference between day and night, and the interference caused by a variable frequency drive. Comparing the impedances of the three line phases, shows differences, which are the result of an asymmetric load. Transfer function measurements show a clear influence of the distance, and also coupling between different phases.
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