©
National Instruments Corporation
3
SCXI-1305 Installation Guide
This icon denotes a caution, which advises you of precautions to take to
avoid injury, data loss, or a system crash.
When this symbol is marked on a
product, refer to the
Read Me First: Safety and Radio-Frequency
Interference
for information about precautions to take.
When symbol is marked on a product, it denotes a warning advising you to
take precautions to avoid electrical shock.
When symbol is marked on a product, it denotes a component that may be
hot. Touching this component may result in bodily injury.
italic
Italic text denotes variables, emphasis, a cross-reference, or an introduction
to a key concept. Italic text also denotes text that is a placeholder for a word
or value that you must supply.
monospace
Text in this font denotes text or characters that you should enter from the
keyboard, sections of code, programming examples, and syntax examples.
This font is also used for the proper names of disk drives, paths, directories,
programs, subprograms, subroutines, device names, functions, operations,
variables, filenames, and extensions.
Configuring Floating or Ground-Referenced Signals
Before installing and using the terminal block, you must determine what
type of signal sources are in the SCXI system. Signal sources are either
floating or ground-referenced.
A
floating source
is not connected in any way to the building ground
system and has an isolated ground-reference point that you cannot assume
is at the same potential as any other ground. Examples of floating sources
include transformers, insulated thermocouples, optical isolators, isolation
amplifiers, and battery-powered devices.
A
ground-referenced
source is connected to the building ground and shares
a common ground with the DAQ device, assuming the computer is
connected to the building power supply. Examples of ground-referenced
signals are the nonisolated outputs of any device that plugs into the building
power supply, such as signal generators and power supplies. Isolated
outputs do not constitute ground-referenced sources and are treated as
floating sources.
Reference an input signal to ground at only one point. Do
not
reference the
input of a differential amplifier module to ground if the signal source is
already ground-referenced. If you are measuring a floating source,
reference the input to ground.
