National Instruments NI PCI-6110 User Manual - Differential Measurements

Chapter 4

Connecting Signals

NI PCI-6110/6111 User Manual

4-10

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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