Detrimental Effects - Campbell CR300 Series Product Manual

17.10.2 Detrimental effects

The harm from a ground loop can be seen in different ways. One consideration is the
electromagnetically induced effect. This will manifest as an AC noise or pulse. As seen in
17-1 (p. 134) the parallel conductive paths form an electrical loop that acts as an antenna to pick
up electromagnetic energy.
FIGURE 17-1. Stray AC magnetic fields picked up in loop antenna
Relatively small electromagnetic energy: This could come from AC current on a nearby
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power cable, or RF energy transmitting through the air, and can cause electrical noise that
either corrupts an analog signal or disrupts digital communications.
Larger electromagnetic energy: The antenna loop scenario can have a more damaging
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effect when a large current is discharged nearby. The creation of an electromagnetic pulse
can induce a surge that damages attached electronic devices.
Another way ground loops affect a system is by allowing ground current to flow between devices.
This can be either a DC or AC effect. For various reasons, the voltage potential between two
different points on the surface of the earth is not always 0 V. Therefore, when two electrical
devices are both connected to a local earth ground, there may exist a voltage difference between
the two devices. When a cable is connected between the two devices at different voltages,
physics dictates than an electrical current must flow between the two points through the cable.
See FIGURE 17-2 (p. 135).
FIGURE
17. Tips and troubleshooting 134