ADLINK PCI-9524 - Manual (Page 49)

Signal Connections 33
ADLINK Technology Inc. PCI-9524
Copyright 2008 User’s Manual
3.2 Analog Input Signal Connections
PCI-9524 provides eight differential analog input channels. To
avoid ground loops and to achieve accurate low-level-signal mea-
surements the PCI-9524 provides only differential input mode.
3.2.1 Signal Sources
Ground-Referenced Signal Sources
A ground-referenced signal is connected in some way to the build-
ings power system. That is, the signal source is already connected
to a common ground point with respect to PCI-9524, assuming
that the computer is plugged into the same power system. Non-
isolated outputs of instruments and devices that plug into the
buildings power system are ground-referenced signal sources.
Floating Signal Sources
A floating signal source is not connected in any way to the build-
ings ground system. A device with an isolated output is a floating
signal source, such as optical isolator outputs, batteries, trans-
former outputs, load-cells and thermocouples.
3.2.2 Input Configurations
Differential input mode for transducer input channels
AI channels 0 to 3 are dedicated to connecting to load-cell trans-
ducers in differential mode.
A load-cell is comprised of four resistive strain-gauges connected
in Wheatstone bridge form, and is inherently a floating differential
output device. Since a load-cell transducer is a passive device, it
requires voltage excitation in order to transform the resistive
change into electrical signals. A typical four-wire connection is
shown on Figure 3-4.