National Instruments NI 783xR User Manual

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National Instruments NI 783xR User Manual Manual pdf 27 page image

Chapter 2 Hardware Overview of the NI 783xRNI 783xR User Manual 2-8 ni.comDifferential Connection Considerations (DIFF Input Mode)In DIFF input mode, the NI 783xR measures the difference between thepositive and negative inputs. DIFF input mode is ideal for measuringground-referenced signals from other devices. When using DIFF inputmode, the input signal connects to the positive input of the instrumentationamplifier and its reference signal, or return, connects to the negative inputof the instrumentation amplifier.Use differential input connections for any channel that meets any of thefollowing conditions:• The input signal is low level (less than 1 V).• The leads connecting the signal to the NI 783xR are greater than3 m (10 ft).• The input signal requires a separate ground-reference point or returnsignal.• The signal leads travel through noisy environments.Differential signal connections reduce noise pickup and increasecommon-mode noise rejection. Differential signal connections also allowinput signals to float within the common-mode limits of theinstrumentation amplifier.Differential Connections for Ground-ReferencedSignal SourcesFigure 2-5 shows how to connect a ground-referenced signal source to achannel on the NI 783xR configured in DIFF input mode.