mechanical vibration frequency

[Crispo]

Hi,

Important Details before I ask my Question:

1. I need to do an experiment that would generally get the frequency of the mechanical vibration response (frequency of the vibration) of a material when stimulated (possibly by impact, tap, and other methods) so I can do analysis on it (Frequency Analysis, Time Frequency Analysis, Wavelet Analysis, etc)

2. Available tools are:

          a) 3-axis accelerometer

          b) Labview Full Development System Version 8.6.1

          c) NI PCI-6251 DAQ

          d) NI PCI-5114

3. This is my first exposure to Labview. I have no experience with this and I'm new to this. So I'm here to ask for support from you guys. I reall need your help.

4. I would have tried learning as much as I can about Labview first before posting a question here but my time is limited for this specific experiment so I had to "dive in" and ask you guys first hand to get a general idea on how to approach this. I am really very unsure how to do this but I think that it is possible to conduct this experiment with Labview because I've read other posts and papers here that have done something very similar to what I need to do.

When I was trying out Labview, I found that it had an NI Sound an Vibration Assistant. But when I tried to open it, it wouldn't open. What are the possible reasons for this?

Can I do the experiment with the given available tools or is the Sound and Vibration Toolkit necessary for it to work?

With my initial readings, I found that the PCI-6251 is what I should use for getting signal.

What VI available from the Labview 8.6.1 Full Development System can I use to:

 -acquire the vibration data and convert it to power spectrum

 -acquire the vibration data and do frequency analysis on it.

I could really use any help I could get right now.

With kind regards,

Jason Ray Crispo

[LV_Pro]

The sound and vibration toolkit is an add-on, you may not have a license for it, in which case it would not activate, or at best, activate for a trial period.

At the moment I can't devote any time to really analyzing your needs, but basically look at the documentation for your DAQ device, and try and determine how to connect to the accelerameter. That is the first challenge. What is the output of the accel? Analog levels, digital messages (not as likely, but who knows these days), what. If analog, what are the expected levels, how should it be hooked up (signal lines, power to the unit, etc.) Then, with that sort of done we can look at how the DAQ needs to be configured to get the best resolution measurement, both in signal level and sampling rate. You will want a moderately high sampling rate, if possible, as you are looking for transient signals and under the Nyquist thereom you need to sample at least twice as fast as the highest frequency expected. Remember, that while your stimulus may be fairly low frequency, what you are probably looking for will be much higher frequency components.

Got to run to a meeting now 😞

Took a quick look at the instruments, not sure if you need the digitizer at this point, but the DAQ card has good high speed specs. What is the output of the accels?

Message Edited by LV_Pro on 02-04-2010 09:50 AM

[Crispo]

Thanks LV_Pro for your resonse.

"The sound and vibration toolkit is an add-on, you may not have a license for it, in which case it would not activate, or at best, activate for a trial period."

  -yes, i think that explains it. I could probably look for a way to make it work for a trial period - that is if this is necessary for the experiment. I'm actually trying out the Sound and Vibration Measurement Suite for a 30-day trial period. Still not sure of which VI to use though.

"basically look at the documentation for your DAQ device, and try and determine how to connect to the accelerameter. That is the first challenge. What is the output of the accel? Analog levels, digital messages (not as likely, but who knows these days), what. If analog, what are the expected levels, how should it be hooked up (signal lines, power to the unit, etc.) "

 -I already connected the accelerometer to the DAQ device. The output is analog..voltage. I'll go look it up right now and give you the details of the set up in a while and also some details about the accelerometer.

"Then, with that sort of done we can look at how the DAQ needs to be configured to get the best resolution measurement, both in signal level and sampling rate. You will want a moderately high sampling rate, if possible, as you are looking for transient signals and under the Nyquist thereom you need to sample at least twice as fast as the highest frequency expected. Remember, that while your stimulus may be fairly low frequency, what you are probably looking for will be much higher frequency components."

-This is where I could really use some help. I'm not so sure how to configure the DAQ for this certain experiment. I do agree that a moderately, or even high if possible, sampling rate would be used since as of now I can't predict range of frequencies of the transient signal. Though the sampling rate could probably be adjusted on the course of the experiment if necessary?

With kind regards,

Jason Ray I. Crispo

[Crispo]

"basically look at the documentation for your DAQ device, and try and determine how to connect to the accelerameter. That is the first challenge. What is the output of the accel? Analog levels, digital messages (not as likely, but who knows these days), what. If analog, what are the expected levels, how should it be hooked up (signal lines, power to the unit, etc.) "

An NI SCB-68 was used to connect the accelerometer to the DAQ device:

a)Accelerometer

     had 6 pins:ST(SelfTest),Vss,X,Y,Z,COM(Ground). Vss = 3V.

     Measurement Range: +3g

     Sensitivity: 300 mV/g

     frequency range: X & Y = 0.5Hz - 1600Hz, Z = 0.5Hz - 550Hz

b) Connections Made = Connector in SCB : Accelerometer pin:

     AI 0 : Z , AI GND : Ground , AI 1 : Y , AI 2 - X

*Note: I only have the trial version of the Sound and Vibration Measurement Suite on another PC. The PC with the DAQ card only runs Labview without the Sound and Vibration Toolkit and Assistant.

in the Labview examples, i tried the "SVXMPL_Vibration Analysis(DAQmx).vi" and "SVXMPL_Transient Analysis(DAQmx).vi" but I can't seem to make them work.

Any thoughts that can help me?

[nayer]

Hello,

Here are some already builting examples that you could use. Example 1 and Example 2 but both of them are using SV toolkit. If you want to do it without toolkit. You can write your own similar to this or use signal processing VIs within LabVIEW.

Thanks

NI-khil

[Crispo]

I can't go with the examples requiring SV toolkit since the trial is already expired.

Anyway, I decided to try to make my own VI which ended up very simplistic. But I'm trying to learn and improve it.

I could really use some help. Currently, the VI i made acquires the signal from the accelerometer using the DAQmx assistant. The waveform is then shown in a waveform graph. My problem now is how to "properly" analyze this signal. I am new in this field (vibration analysis). Although i found a function that gets the power spectrum of the graph, i don't think it is right to simply connect the raw signal to the power spectrum function. I'm thinking the noise would have to be filtered? Then there's also the voltage offset.. and do i need to integrate the signal once(velocity) or twice(displacement) before I get the frequency spectrum of the waveform?

[preston_johnson]

All of the functions you are looking for are included in the Sound and Vibraiton measurement suite, including a nice impact hammer test that provides a frequency response and helps to remove noise.  Integration is also provided. 

Many of our customers use a DSA device, such as the USB-9234 which provides power to the accelerometer AND provides AC coupling to remove the DC offsett and finally ANTI-Aliasing filters to remove noise. 

These tools will save you a lot of time and frustration. 

[Crispo]

---

preston johnson wrote:

All of the functions you are looking for are included in the Sound and Vibraiton measurement suite, including a nice impact hammer test that provides a frequency response and helps to remove noise.  Integration is also provided. 

Many of our customers use a DSA device, such as the USB-9234 which provides power to the accelerometer AND provides AC coupling to remove the DC offsett and finally ANTI-Aliasing filters to remove noise. 

These tools will save you a lot of time and frustration. 

---

For future experiments that involve vibration analysis i would definitely recommend the Sound and Vibration measurement Suite to our company. But for this case, I can't request for those yet since this is only supposed to be a simple and low-cost experiment which gets the frequency of the vibration of a material when the material is allowed to vibrate.

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In my block diagram, why doesn't the DAQ Assistant allow me to have an acceleration task? I'm currently getting data from the accelerometer through a voltage task and it makes sense since the output of the accelerometer is voltage. But it just makes me wonder why an accelerometer is not recognized in an acceleration task.