Differential measurements, Table 4-4. signal source types, Differential connection considerations – National Instruments NI PCI-6110 User Manual
Page 40: Differential measurements -10, Differential connection considerations -10
Chapter 4
Connecting Signals
4-10
ni.com
Differential Measurements
The following sections discuss the use of differential (DIFF) measurements
and considerations for measuring both floating and ground-referenced
signal sources.
Table 4-4 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 NI PCI-6110/6111 AI signal
has its own reference signal or signal return path. The device 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 noise pickup and increase
common-mode noise rejection. Differential signal connections also allow
input signals to float within the common-mode limits of the PGIA.
Table 4-4. 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