We are using two different DAQ cards (PXI-6225 and PXI-6070E) mounted
on a PXI Chassis to acquire data from different types of sensors. We
had a LabView application built for this purpose. We are able to
change the channel configuration depending on the type of sensors we
want to use. On the current setup we intend to use 64 differential
pressure tranducers from Setra, model 265, which have a 0-5 VDC output
and use a 24 VDC excitation. These transducers use the changes in
capacitance on the circuit to translate it to changes in pressure.
All channels are configured as NRSE and the first configuration
consisted of all 64 single-ended channels connected to a SCB-68
connector block and then to the PXI=6225. When we tried to connect all
64 sensors we found noise problems on the signals we acquired, so we
started troubleshooting. We got 48 of 64 sensors to read acceptable
data with reduced levels of noise. When attempting to connect the
remaining 16 channels none of the configurations seemed to work. All
the shieldings in the cables were referenced to the common and still
noise didn't drop on those channels.
Then we decided to connect those 16 channels through the other card,
PXI-6070E. Noise levels were reduced, but we noticed that some of the
transducers showed offsets in the "zero". We recalibrated the sensors,
double-checked the settings, and once we connected them back to the
system, the 0.2V-0.4V offset appeared again. Also we noticed that in
the previous 48 channels two of the sensors showed considerable levels
of noise. We tried swithching sensors, checking the cables, shielding,
location on the test specimen, and still can't figure out the source of
the noise.
Talking with the company that developed the LabView application, they
mentioned that the DAQ card may be generating the noise issues. How
can we confirm this and is this a possibility?
Any feedback is welcomed.
Thanks,
Roy.
