ADLINK USB-1903 - Manual (Page 39)

Hardware Information 25
USB-1900 Series
To avoid ground loops and obtain more accurate measurement
from the A/D conversion, it is important to understand the type of
signal source and how to choose the analog input modes from
among Referenced single-end (RSE), Non-Referenced single-end
(NRSE), and Pseudo-Differential Input (PDIFF).
2.3.1 Signal Source Types
Floating
A floating signal source is not connected in any way to the
existing ground system. A device with an isolated output is a
floating signal source. This includes optical isolator outputs,
transformer outputs, and thermocouples.
Ground-Referenced
A ground-referenced signal is connected in some way to the
existing ground system. That is, the signal source is already
connected to a common ground point with respect to the
USB-1900 series, assuming that the computer is connected to
the same power system. Non-isolated outputs of instruments
and devices that plug into the existing power systems are
ground-referenced signal sources.
2.3.2 Input Configurations
Single-End Connections
A single-end connection is used when the analog input signal is
referenced to a ground that can be shared with other analog
input signals. There are two types of single-end connections:
RSE and NRSE configuration. In RSE configuration, the
USB-1900 Series provides the grounding point for external
analog input signals and is suitable for floating signal sources.
In NRSE configuration, the USB-1900 Series does not provide
the grounding point. The external analog input signal provides
its own reference grounding point and is suitable for
ground-referenced signals.
Referenced Single-End (RSE) Mode
In referenced single-end mode, all input signals are connected
to the ground provided by the USB-1900 Series, as shown.