| 摘要 |
A sensing unit comprising sensor means enclosed in a casing made of a ferromagnetic material, to achieve a ferromagnetic shield. The sensing unit may further include signal processing means, also enclosed in the ferromagnetic casing. A distributed system for measuring, processing and displaying information from a plurality of sensors comprises a plurality of sensor units. A method for quick detection of offenders of oil, gas or other pipes, by monitoring the protective cathodic voltage and detecting quick changes in the voltage. A method for detecting leakage from a pipe using multiple channels/inputs, wherein a low frequency range input measures seismic noises, and a high frequency range input measures cavitation noises, and wherein a leakage indication is issued if both the low frequency and high frequency noises are simultaneously detected.
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