Hi all,
I am experiencing some weird steplike baseline shifts in my IEPE acceleration measurements using my CRIO-9047 with NI9320 cards after swtiching the system from using DAQmx to FPGA.
System Setup
Two systems in together, a crio and ethercat expansion:
cRIO-9047 with FPGA VI (DMA FIFO to RT app → TDMS logging).
NI-9145 EtherCAT chassis with FPGA VI (UDVs to RT app → TDMS logging).
Both use NI-9230 modules with piezoelectric accelerometers (IEPE).
Scaling is applied in the RT app for both systems.
Data types on both FPGA paths: FXP 24,7.
Problem
On the cRIO-9047 system, channels show large, random low-frequency baseline drifts and transient steps (see attached plots).
On the NI-9145 system, the data are mostly stable but show softer baseline wandering.
With the same sensors/modules in the cRIO-9047, when previously sampled for ~5 years using DAQmx, there was no drift.
Observations
The drift looks like a vbias wander, not real structural motion (piezo sensors are AC-coupled).
Only appears when using FPGA I/O nodes; not seen in DAQmx mode.
The FPGA code is simple: read module channels → write to FIFO → RT logging. No filtering or scaling on FPGA.
Wondering if there is a manual configuration setting for DC/AC coupling or bias removal on the NI-9230 when accessed via FPGA I/O that is missing compared to DAQmx.
Question for NI
1) Is there a required configuration step (DC coupling, bias adjust, HPF setting, etc.) for NI-9230 modules when used in FPGA mode?
2) Why would the same hardware/sensors be stable under DAQmx, but exhibit baseline drift when accessed through FPGA I/O?
3) Are there best practices for preventing these very low-frequency drifts (e.g., explicit high-pass, configuration register, or FPGA property node settings)?
I've attached the whole project below. The code is relatively simple and maybe a little backwards (I am a structural engineer!), but I don't see where anything would be causing this.... In the attached image, the wandering sensors are ch1-ch14, which are on the crio, and the ch15 to ch21 are on the EtherCAT chassis.
Thanks!
Ethan
