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Care must be exercised in this type of application, however, as the PXIe-4480 does not provide
some of the features of a true strain measurement module, specifically remote sense of the
excitation voltage. Without remote sense, the voltage present at the bridge will be slightly less
than output by the module, due to the presence of lead wire resistance. Without compensation,
this difference would translate into measurement error.
To mitigate this effect, however, the voltage source is adjustable in a nominal range of 9.5 V to
12 V. During initial system setup, the bridge voltage would be externally measured and the
voltage source iteratively adjusted until the desired bridge excitation voltage is achieved.
For maximum flexibility, the module’s voltage excitation selection is programmable on a
per-channel basis.
Fault Conditions
IEPE Open and IEPE Short
When IEPE is enabled, the PXIe-4480 monitors the output voltage to detect if there is a
connection issue with the attached signal source. Common connection issues that can occur
include open and short circuits. An open circuit occurs if there is a disconnect between the signal
source and the module, resulting in the output voltage rising too high. A short circuit occurs if
the module inputs have been shorted, for example due to a sensor fault, resulting in the output
voltage falling too low. If an open or short event occurs, the hardware will continue to perform
the programmed acquisition, but turn the Active LED red and set a flag that can be queried by
the user.
Refer to the
Open Current Loop Detection
and
Overcurrent Detection
topics of the
NI-DAQmx
Help
for more information on how to use the IEPE Open or IEPE Short feature.
Voltage Excitation Current Limit
When the voltage source is enabled, the PXIe-4480 monitors the output current. If the current
exceeds its specified maximum value, the source will continue to operate, but its voltage
regulation will be degraded. In addition, the hardware will turn the Active LED red and set a flag
that can be queried by the user. Refer to the
Excitation Fault Detection
topic of the
NI-DAQmx
Help
for more information on how to use the Voltage Excitation Current Limit detection.