ADLINK cPCI-9116 - Manual (Page 26)

16
• Signal Connections
3.2 Analog Input Signal Connection
The 9116 series provides up to 64 single-ended or 32 differential analog input
channels. You can set and fill the Channel Gain Queue to get the desired
combination of the input signal types. The analog signals can be converted to
digital value by the A/D converter. To avoid ground loops and to obtain
accurate measurements from the A/D conversion, it is quite important to
understand the signal source type and how to choose the analog input modes:
Single-ended, Differential, or User Common Mode.
3.2.1 Types of signal sources
Floating Signal Sources
A floating signal source means it is not connected in any way to the buildings
ground system. A device with an isolated output is a floating signal source,
such as optical isolator outputs, transformer outputs, and thermocouples
Ground-Referenced Signal Sources
A ground-referenced signal means it is connected in some way to the buildings
system. That is, the signal source is already connected to a common ground
point with respect to the 9116 card, 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.
3.2.2 Input Configurations
Single-ended Mode
In single-ended mode, all input signals are connected to ground provided by
the 9116 card. It is suitable for connections with floating signal sources. Figure
4 illustrates single-ended connection. Note that when more than two floating
sources are connected, these sources will be referenced to the same common
ground.
AIn
AGND
n = 0, ...,63
Floating
Signal
Source
Instrumentation
Amplifier
To A/D
Converter
Input Multipexer
V1 V2
+
- +
-
J1
Figure 4: Single-ended Mode and Floating sources