Signal Connection to External Devices
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DS1104 Hardware Installation and Configuration March 2004
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Definitions of Different Ground Signals
There are three 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.
■ 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.
■ 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.
■ 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.
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