© National Instruments | 4-13M Series User ManualWith 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 Floating SignalSources section for more information about NRSE connections.When to Use Referenced Single-Ended (RSE)Connections with Floating Signal SourcesOnly use RSE input connections if the input signal meets the following conditions:• The input signal can share a common reference point, AI GND, with other signals thatuse RSE.• 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).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 Referenced Single-Ended (RSE) Connections for Floating Signal Sourcessection for more information about RSE connections.Using Differential Connections for Floating SignalSourcesIt is important to connect the negative lead of a floating source to AI GND (either directly orthrough a bias resistor). Otherwise, the source may float out of the maximum working voltagerange of the NI-PGIA and the DAQ device returns erroneous data.The easiest way to reference the source to AI GND is to connect the positive side of the signalto AI+ and connect the negative side of the signal to AI GND as well as to AI- without usingresistors. This connection works well for DC-coupled sources with low source impedance (lessthan 100 Ω).Note (NI USB-62xx BNC Devices) To measure a floating signal source on USBBNC devices, move the switch under the BNC connector to the FS position.Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
