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A telluric current (from Latin tellūs 'earth'), or Earth current, [1] is an electric current that flows underground or through the sea, resulting from natural and human-induced causes. These currents have extremely low frequency and traverse large areas near or at Earth 's surface.
The first soil resistance measuring instrument was invented in the 1950s by Evershed & Vignoles Meggers who made the first insulation and earth resistance testers. [2] One of the most used analog grounding testers in USSR were М416. [3] From the 21st century several companies produced digital earth resistance meters and testers.
The tester has output overload protection. The test voltage may be either direct current or alternating current at power frequency or other frequency, like resonant frequency (30 to 300 Hz determined by load) or VLF (0.01 Hz to 0.1 Hz), when convenient. The maximum voltage is given in the test standard for the particular product.
For instance, if a current of 1 mA at the local power frequency is induced in the ground loop, and the resistance of the screen of the signal cable is 100 mΩ, the voltage drop will be = = 100 μV. This is a significant fraction of the output voltage of a moving coil pickup cartridge, and imposes an objectionable hum on the cartridge output.
Doc Lew Childre Jr. (born September 7, 1945) [1] (pronounced "Chill-dree") [2] is an American author [3] and the founder of the Heartmath Institute, a non-profit organization whose objective is to help the development of "heart-brain-coherence". He works on child development and strategies for dealing with stress.
The fundamental Schumann resonance is at approximately 7.83 Hz, the frequency at which the wavelength equals the circumference of the Earth, and higher harmonics occur at 14.1, 20.3, 26.4, and 32.4 Hz, etc. Lightning strikes excite these resonances, causing the Earth–ionosphere cavity to "ring" like a bell, resulting in a peak in the noise ...
The rotation rate of the Earth (Ω = 7.2921 × 10 −5 rad/s) can be calculated as 2π / T radians per second, where T is the rotation period of the Earth which is one sidereal day (23 h 56 min 4.1 s). [2] In the midlatitudes, the typical value for is about 10 −4 rad/s.
The Numerical Electromagnetics Code, or NEC, is a popular antenna modeling computer program for wire and surface antennas. It was originally written in FORTRAN during the 1970s by Gerald Burke and Andrew Poggio of the Lawrence Livermore National Laboratory .