National Instruments DAQ Series User Manual

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National Instruments DAQ Series User Manual Manual pdf 26 page image

Chapter 3 Connecting Signals© National Instruments Corporation 3-7 DAQCard-700 User ManualRecommended Input ConfigurationsThe following sections discuss the use of RSE and DIFF measurements andconsiderations for measuring both floating and ground-referenced signalsources. Table 3-1 summarizes the recommended input configurations forboth signal source types.Single-Ended Connection ConsiderationsSingle-ended connections are those in which all DAQCard-700 AI signalsare referenced to one common ground. The input signals are tied to thepositive input of an operational amplifier that is referenced to the commonground point.When the DAQCard-700 is configured for RSE input mode, 16 AI channelsare available. You can use single-ended input connections when thefollowing criteria are met by all input signals:• Input signals are high level (greater than 1 V).• Leads connecting the signals to the DAQCard-700 are less than 15 ft.• All input signals share a common reference signal (at the source).If any of the preceding criteria are not met, use the DIFF input mode.The RSE input mode is referenced, but you can use this mode fornonreferenced signal sources. In addition, if the computer using theTable 3-1. Recommended Input Configurations for Ground-Referenced and Floating Measurement SystemsSystem Type Type of SignalRecommended InputConfigurationsGround-referenced system,such as a desktop computerGround referenced(nonisolated outputs,plug-in instruments)DIFFFloating(batteries, thermocouples,isolated outputs)DIFF with bias resistorsRSEFloating system, such as abattery-powered computerGround referenced(nonisolated outputs,plug-in instruments)DIFF with bias resistorsRSEFloating(batteries, thermocouples,isolated outputs)DIFF with bias resistorsRSE