The electric power distribution systems that supply our electric power use earth ground as their reference. As a result , currents flow in the earth from these systems. Because power system are used so extensively throughout the world, it can be assumed that these earth currents (at 60 Hz) flow almost everywhere. Such currents cause a potential drop(voltage) to exist between separate points on the earth (typically 1-10V rms). If a measurement system is grounded to earth at two separate point of the earth's surface, it must be assumed that a potential drop will appear between these two point. The two ground connections will have caused a ground loop to be established, and large amounts of unwanted 60-Hz current will probably flow in this loop. If the shield of a measuring system constitutes part of such a loop, the shield itself becomes a source of interference( rather than the barrier to noise that it is designed to be)
Inductive pickup by a ground loop occurs the same way as inductive pickup in any closed conducting loop. Since a ground loop has a relatively large area and very low impedance, inductive pickup from stray magnetic or electromagnetic field in the measurement environment can occur quite easily. Orthodox shielding methods are not as effective against inductive pickup in ground loop because the shielding conductors and the ground plane themselves form a part of the loop
The electric power distribution systems that supply our electric power use earth ground as their reference. As a result , currents flow in the earth from these systems. Because power system are used so extensively throughout the world, it can be assumed that these earth currents (at 60 Hz) flow almost everywhere. Such currents cause a potential drop(voltage) to exist between separate points on the earth (typically 1-10V rms). If a measurement system is grounded to earth at two separate point of the earth's surface, it must be assumed that a potential drop will appear between these two point. The two ground connections will have caused a ground loop to be established, and large amounts of unwanted 60-Hz current will probably flow in this loop. If the shield of a measuring system constitutes part of such a loop, the shield itself becomes a source of interference( rather than the barrier to noise that it is designed to be) Inductive pickup by a ground loop occurs the same way as inductive pickup in any closed conducting loop. Since a ground loop has a relatively large area and very low impedance, inductive pickup from stray magnetic or electromagnetic field in the measurement environment can occur quite easily. Orthodox shielding methods are not as effective against inductive pickup in ground loop because the shielding conductors and the ground plane themselves form a part of the loop
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