Problem with accelerometer data

[Alex01]

Hello,

I'm new to LabView and am trying to set up a vibration measurement system.  We have a PXI-4472 and a tri-axial accelerometer plugged into the first 3 channels of the PXI-4472.

I used the DAQ Assistant in LabView and simply set up the three input channels as analog signals and had it output to a waveform graph.  When I run the VI, I can see all 3 axes of the accelerometer being plotted but the scaling appears to be way off.  I've set it up to display in terms of G, rather than m/s^2.  Even when I subject the accelerometer to some significant vibration, the graph indicates that it's less than 0.02g.

What am I doing wrong?  Do I need a inline charge amplifier between the accelerometer and the PIX-4472?  Do I have to enable IEPE in LabView or Measurement & Automation Explorer?  If so, how do I do it?  My experience with LabView is extremely limited and I don't have much theoretical knowledge of vibration and acceleration.

I'm running LabView 8.2, DAQmx version 8.5, MAX version 4.2.1.

My hardware setup is a PXI-1042 chassis, PXI-8186 controller, and a PXI-4472 card.  I'm also using a Kistler 8290A tri-axial accelerometer: datasheet.

Thanks,

Alex

[Alex01]

Here's the "code" I was using.  As you can see, I have a lot of learning to do with LabView.

[mikeporter]

The output from an accelerometer is a very low-level signal. You need an amplifier like the one mentioned in the accelerometer's datasheet - and the amp should be as close as possible to the accelerometer to eliminate as much cable length as you can.

Mike...

[Alex01]

My understanding was that the PXI-4472 has built-in capabilities that support things like signal amplification and conditioning.  If memory serves correctly, I believe NI told us that the PXI-4472 was specifically designed for sound and vibration measurements and that it should work with our proposed setup.

Is there anything in the Sound and Vibration Toolkit that would help in terms of signal amplification or scaling?  At this point in time, we're trying to avoid having to buy additional hardware for budget reasons.

-Alex

[mikeporter]

It very well might, but I still prefer the external amps because if the signal conditioning is on the acquisition card you have to run the low-level accelerometer signals all the way to the PC. This can lead to noise and generally degraded signals. A good rule is to keep signal conditioning as close to the signal source as you can.

Mike...

[AnalogKid2DigitalMan]

As Mike mentioned, you need to use the charge amplifier to convert the accelerometer's signal into an analog voltage. You cannot do this though software.

See below for recommended charge amplifier.

http://www.kistler.com/medias/vdEXyQLezgCxP85D8YwBEd-30.pdf