National Instruments PCI-6110E/6111E - Manual (Page 43)

Chapter 4 Signal Connections
PCI-6110E/6111E User Manual 4-10 © National Instruments Corporation
Table 4-3 summarizes the recommended DIFF signal connections and
includes input examples for both types of signal sources.
Differential Connection Considerations
A differential connection is one in which the 611X E board analog input
signal has its own reference signal or signal return path. The 611X E
channels are always configured in DIFF input mode. The input signal is
tied to the positive input of the PGIA, and its reference signal, or return,
is tied to the negative input of the PGIA.
Each differential signal uses two inputs—one for the signal and one for
its reference signal.
Differential signal connections reduce picked up noise and increase
common-mode noise rejection. Differential signal connections also
allow input signals to float within the common-mode limits of the
PGIA.
Table 4-3. Signal Source Types
DIFF Input
Examples and
Signal Source
Floating Signal Source
(Not Connected to Building Ground) Grounded Signal Source
Input Examples • Ungrounded Thermocouples
• Signal conditioning with isolated
outputs
• Battery devices
• Plug-in cards with nonisolated
outputs
Differential
(DIFF)
See text for information on bias resistors.
+
-
+
-
ACH0(+)
ACH0(-)
ACH0GND
V
1
+
-
+
-
ACH0(+)
ACH0(-)
ACH0GND
V
1
PCI_E.book Page 10 Thursday, June 25, 1998 12:55 PM