07-15-2009 05:26 PM
Using LabVIEW 8.6, a CDAQ and NI-9234 with either a 3-axis or single axis IEPE accelerometer.
I need to measure several variables at different frequencies at the same time:
p-p Displacement below 1.4Hz
Peak acceleration from 1.4Hz to 20Hz
Peak velocity above 20Hz.
Sounds weird, but those are what I'm required to find.
I do not have the sound and vibration toolkit, but I figure this stuff can be done with the Labview Math and signal processing toolkits.
My knowledge of vibration measurement is limited, but if anyoen can point me in the right direction that would be greeeaaaaat (Lumburgh)....
Thanks for the help!
07-16-2009 12:52 PM
07-16-2009 01:13 PM
07-23-2009 04:04 PM
Ok, so aI downloaded the 30-day trial of sound and vibe.
Having some trouble with the filtering. Using the FIR filter from the toolkit, I set it for bandpass with the parameters of 1.3, 1.5, 19, 21. This is for the peak acceleration data.
When I run the VI, I get error 21411 sayingthat the settings are incorrect. As I realize the filter doesn't know what I'm trying to do, I think maybe my settings are simply outside the capabilities of it.
Any ideas?
07-24-2009 06:16 PM
Hi John,
I don't think that we need to the Sound and Vibration toolkit for this, but in the interest of trouble shooting that, could you post your code and a screenshot of the error message? That would help me spot the problem.
Were you ever able to get this up and running in just LabVIEW? If you were still interested in doing this, what I might recommend would be:
Take the acceleration data and use 3 Filter Express VIs as low, band, and highpass filters to divided the data into your ranges of interest: I dont remember what they were, something like 0- 1.4 kHz, 1.4-20kz, 20 kHZ+. You can then use the Time Domain Math Express VI to integrate to get the velocity information. We also have peak search VIs.
Regards,
Mallori
07-24-2009 07:00 PM
I've changed my code since then but I basicallly had a 3-axis accelerometer in DAQ assistant wired to the FIR filter. I set the filter to "Bandpass" and was having troublegetting it to pass the band between 1.4 and 20 Hz. Maybe I just don't understand what to put in for the four parameters.
What I wrote in my post is exactly what the error says.
07-31-2009 03:48 PM
I'm starting to think this may be impossible with the setup I have because it won't allow DC coupling since I'm using IEPE and I need to measure some pretty low frequencies.
Anything?
08-03-2009 07:02 PM
Hi John,
The 9234 is capable of DC coupling, you just have to enable it in the DAQ Assistant. On the Devices tab, seen in the attached screenshot, you can select DC coupling from the drop down menu. This will now allow the low frequency signals to pass through. Are you still having
Regards,
Mallori
08-04-2009 10:14 AM - edited 08-04-2009 10:18 AM
Nope. When IEPE excitation and DC coupling are enabled at the same time, LabView gives me error -201172: "Measurement: AI channels on this device do not support using DC coupling while using IEPE excitiation."
Yesterday I learned from the good folks at PCB that the accelerometers I'm using (PCB 604B31 and 608A11) are not even capable of DC acceleration measurement. They are strictly for vibration.
I am now looking at buying some new accelerometers for that issue. PCB MEMS models will fulfill this, but they need an external power source and probably won't even need the 9234 module as they just output a voltage so I can probably use the 9221 modules.
Still learning about this stuff.
08-04-2009 01:10 PM - edited 08-04-2009 01:11 PM
Ok, so here's what I have so far.
All the filters are 29 tap FIR filters.
The program seems to work ok, but I really have no feel for how it should operate since I have no calibration source at the moment.
I also am unsure which type of filter is more useful.
Edited for typo.