User manual

UniversitàdegliStudidiCatania
IntroductiontoNILabVIEW
 DAQ:Grounding
Voltage is not absolute; it always requires a reference to be meaningful. Voltage is
always the measure of a potential difference between two bodies. One of th ese bodies is
usually picked to be the reference and is assigned "0 V." So to talk about a 3.47 V signal
really means nothing unless we know with respect to what reference.
Earth ground
refers to the potential of the earth below your
feet. Most electrical outlets have a prong that connects to the
earth ground, which is also usually wired into the building
electrical system for safety. Many instruments also are
"grounded" to this earth ground, so often you'll hear the term
system ground. The main reason for this type of grounding is
safety, and not because it is used as a reference potential. In fact,
you can bet that no two sources that are connected to the earth
ground are at the same reference level; the difference between
them could easily be up to 10 volts.
Reference ground, sometimes called a return path or signal
common, is usually the reference potential of interest. The
common ground may or may not be wired to earth g round. The
point is that many instruments, devices, and signal sources
provide a reference (the negative terminal, common terminal,
etc.) that gives meaning to the voltages we are measuring.
DIEEI