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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.

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

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