© National Instruments Corporation 11 NI USB-9229/9239 User Guide and Specifications

Connecting Signal Sources to the NIUSB-9229/9239

You can connect ground-referenced or floating signal sources to the
NIU SB-9229/9239. If you make a ground-referenced connection between
the signal source and the NI USB-9229/9239, make sure the voltage on
the AI+ and AI– connections are in the channel-to-earth safety voltage
range to ensure proper operation of the NIU SB-9229/9239. Refer to the
Specifications section for more information about operating voltages and
overvoltage protection.
Figures 8 and 9 illustrate connecting grounded and floating signal sources
to the NI USB-9229/9239.
Figure 8. Connecting a Grounded Signal Source to the NI USB-9229/9239
Figure 9. Connecting a Floating Signal Source to the NI USB-9229/9239
NI USB-9229/9239 Circuitry
The NI USB-9229/9239 analog input channels are floating with respect to
earth ground and each other. The incoming analog signal on each channel
is conditioned, buffered, and then sampled by a 24-bit Delta-Sigma ADC.
NI USB-9229/9239
Signal
Source
AI–
+
–
AI+
NI USB-9229/9239
Signal
Source
AI–
+
–
AI+