4-18 | ni.comChapter 4 Analog InputWhen to Use Differential Connections withGround-Referenced Signal SourcesUse DIFF input connections for any channel that meets any of the following conditions:• The input signal is low level (less than 1 V).• The leads connecting the signal to the device are greater than 3 m (10 ft).• The input signal requires a separate ground-reference point or return signal.• The signal leads travel through noisy environments.• Two analog input channels, AI+ and AI-, are available.DIFF signal connections reduce noise pickup and increase common-mode noise rejection. DIFFsignal connections also allow input signals to float within the common-mode limits of theNI-PGIA.Refer to the Using Differential Connections for Ground-Referenced Signal Sources section formore information about differential connections.When to Use Non-Referenced Single-Ended (NRSE)Connections with Ground-Referenced Signal SourcesOnly use non-referenced single-ended input connections if the input signal meets the followingconditions:• The input signal is high-level (greater than 1 V).• The leads connecting the signal to the device are less than 3 m (10 ft).• The input signal can share a common reference point with other signals.DIFF input connections are recommended for greater signal integrity for any input signal thatdoes not meet the preceding conditions.In the single-ended modes, more electrostatic and magnetic noise couples into the signalconnections than in DIFF configurations. The coupling is the result of differences in the signalpath. Magnetic coupling is proportional to the area between the two signal conductors. Electricalcoupling is a function of how much the electric field differs between the two conductors.With this type of connection, the NI-PGIA rejects both the common-mode noise in the signal andthe ground potential difference between the signal source and the device ground.Refer to the Using Non-Referenced Single-Ended (NRSE) Connections for Ground-ReferencedSignal Sources section for more information about NRSE connections.Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
