VersaLogic VL-12CT96, Reference Manual

Page: 16 / 71

2-10
VL-12CT96/7 Analog & Digital I/O Card
Differential Mode
Differential mode is used for signals that are not referenced to a common ground point. Each input
signal is represented as a voltage difference between two signal conductors (usually twisted wires), and
is presented to the board as a (+) and (–) pair. Differential mode reduces the effects of electromagneti-
cally induced noise and ground currents in electrically noisy environments. It is especially useful in
eliminating the effects of common mode noise generated on input lines over longer distances. Eight
input channels are available in differential mode.
CHANNEL 1
CHANNEL 0
+
V1
-
V0
+
-
4
5
2
1
VL-12CT96
V1
11
9
5
3
7
1
12
10
6
4
8
7
9
8
10
VL-12CT97
2
3
1
5
2
4
6
V6
OPTIONAL
-
+
-
+
2 6 4
3 5
1
V7
SEE
TEXT
Figure 2-8. Differential Input Mode
Note that in full differential operation a return path must be provided for the bias currents of the input
amplifier. An on-board 1M
Ω
resistor is provided for this purpose. Jumper V1[11-12] should be
inserted.
In noisy electrical environments, the bias resistor should be located in close proximity to the voltage
source. Jumper V1[11-12] should be removed under these conditions.
Jumper Jumper Jumper Jumper Jumper As As As As As
Block Block Block Block Block Description Description Description Description Description Shipped Shipped Shipped Shipped Shipped
V1[11-12] Differential Bias Resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . In Circuit
In – In Circuit
Out – Disconnected
Figure 2-9. Bias Resistor
Configuration — Analog Input