ADLINK PCM-9112+ - Manual (Page 42)

34 • Operation Theory
4.2 Analog Input Signal Connection
The PCI-9112 provides 16 single-ended or 8 differential analog input
channels. The analog signals can be converted to digital value by the A/D
converter. To avoid ground loops and to obtain more accurate measurements,
it is quite important to understand the signal source type and how to choose
the analog input modes: signal-ended or differential. The PCI-9112 offers
jumpers to select 16 single-ended or 8 different analog inputs.
Single-ended Mode
The single-ended mode has only one input relative to ground and is suitable
for connecting with a floating signal source. A floating source is one that does
not have any connection to ground. Figure 4.2.1 shows the single-ended
connection. Note that when more than two floating sources are available, the
source must be with common ground.
AIn
AGND
n = 0, ..., 15
Floating
Signal
Source
Operational
Amplifier
To A/D
Converter
Input
Multipexer
Figure 4.2.1 Floating source and single-ended
Differential input mode
The differential input mode provides two inputs that respond to differences in
signals. If the signal source has one side connected to local ground, the
differential mode can be used to reduce the effect of ground loops. Figure
4.2.2 shows the connection for differential input mode. However, if the signal
source is locally grounded, the single-ended mode can be used when the
Vcm (Common Mode Voltage) is very small and the effect of ground loops is
minimal.