National Instruments NI USB-9234 User Manual page 12

Connecting Signal Sources to the NI USB-9234
NI USB-9234 User Guide and Specifications
You can connect ground-referenced or floating signal sensors to the
NI USB-9234. To avoid picking up ground noise, use a floating
connection. To further minimize ground noise, prevent the metal shells of
the BNC connectors from touching each other, the modules, or the chassis.
If you make a ground-referenced connection between the signal source and
the NI USB-9234, make sure the voltage on the AI– shell is in the
common-mode range to ensure proper operation of the NI USB-9234. The
AI– shell is protected against accidental contact with overvoltages within
the overvoltage protection range. Refer to the
more information about operating voltages and overvoltage protection.
Figures 7 and 8 illustrate connecting grounded and floating signal sources
to the NI USB-9234.
Signal
Source
+
–
Figure 7. Connecting a Grounded IEPE Sensor to the NI USB-9234
Figure 8. Connecting a Floating IEPE Sensor to the NI USB-9234
The NI USB-9234 can also provide an IEPE excitation current for each
channel to measure ground referenced or floating IEPE sensors. Typical
IEPE sensors have a case that is electrically isolated from the IEPE
electronics, so connecting the sensor to the NI USB-9234 results in a
floating connection even though the case of the sensor is grounded.
AI+
Common-
AI–
Mode
Voltage
Signal
AI+
Source
+
NI USB-9234
–
AI–
12
Specifications section for
NI USB-9234
ni.com