Definitions of Different Ground Signals
There are four classes of signals often referred to as ground signals,
i.e. signal return, power ground and shield. To achieve the best
results regarding signal quality, noise rejection and EMC behavior,
these different ground signals must not be mixed.
n A signal return line is the reference potential of a signal. It should
carry the same current as the corresponding signal line, and this
current should be kept small.
n Power supply ground is the return path for the supply voltage. It
carries large and varying currents resulting in significant (AC)
voltage drops along the cable. Never use the same wire for signal
return and power supply ground.
n Shield is a barrier to keep in everything inside and keep out
everything outside. It is usually connected to the device enclosures
at both ends to form a closed cage around all signals and cards. It
is not necessarily connected to power ground.
n Protective earth (PE) is a reference point, which has the same
potential as the surrounding earth. Connections to protective
earth are intended for safety purposes.
Terms and their definitions
Grounding Signals
Do not use a ground line for more than one purpose. A grounding
scheme has to be evaluated based on its AC current flow and not on
its DC behavior. The DC resistance of a cable has only minor impact.
Cable inductance plays a major role.
General
To avoid ground loops and ground bounces, use separate signal
return (ground) lines for all connected sensors and actuators.
Each signal should have its own return line. The best results can be
achieved with a shielded twisted pair cable. A twisted pair cable has
the lowest inductance.
Avoiding ground loops and
ground bounces
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Grounding and Shielding
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