https://www.mktester.com/ground-resistance-tester/earth-ground-resistance-tester.html
Earth ground resistance tester is a high-precision testing instrument used in various fields such as substations to test grounding resistance and related parameters.The instrument is of an integrated structure, with a built-in frequency conversion power supply module, and the output power supply is continuously variable in frequency. The frequency can be changed to 45Hz or 55Hz, the high-speed processor core is built in, and the high-end digital filtering technology is adopted, thus effectively avoiding the interference of power frequency electric field to the test and fundamentally solving the difficult problem of accurate measurement under strong electric field interference.