Analog Devices ADXL210 VI

[Kave Man]

Like many others posting here, I am a noob to LabVIEW and would like to tap into more knowledgeable minds.  My equipment is as follows:

10 ADXL210 accelerometers (using PWM output, 50 Hz analog bandwidth, and 500 Hz modulator frequency)

NI-PCI 6229 DAQ card

SCB-68

LabVIEW 7.1.1

Going over the tutorials gave me a general comfort level when using this program, but I couldn't find much to help me towards developing a VI to collect the signals from multiple accelerometers using pulse width modulation and convert their values into acceleration.  Is there a tutorial I'm missing that addresses this type of sensor I can model mine after or am I left to make one from scratch myself?  Thanks

[garretth]

Kave Man,

Your acceleration is dependent on the PWM reading so you should just need to calculate the Duty Cycle of your signal. The best way to do this is by using the onboard counters of your 6229. Take a look at the example called Meas Duty Cycle - Buffered Finite.vi. You can find it by searching for "duty" in the LabVIEW example finder. The example is documented and explains how to connect your accelerometer to your DAQ card.

Cheers,

[Kave Man]

Thanks for the help, Garrett.  After reading your post with the suggested Meas Duty Cycle-Buffered-Finite.vi file and using a search for that in this forum, it appears that this is a fairly well-asked about topic.  I searched for it and browsed the folders trying to find it.  Unfortunately I don't have a DAQmx folder under Hardware Input and Output.  Am I missing seperate software or is there something else I'm overlooking?

[garretth]

You will need the DAQmx driver. Check to see if it is already installed. You can do this from the Measurement and Automation Explorer program. Expand the Software folder under "Configuration." You should see NI-DAQmx listed there. If you don't, then you will need to install this driver either off of the CD that came with your 6229 or from ni.com. If it is currently installed, then it is possible that the support files were not installed. You can go to the Add/Remove Software to do a "Repair" on the DAQmx driver.

http://digital.ni.com/softlib.nsf/websearch/7FEAEE6A4B4AA836862571C00064E6CA?opendocument&node=132060_US

Hopefully that helps,

[Kave Man]

Thanks again, Garrett.  I got everything installed nicely and looked over the example VI.  Here's where I'm having major issues.  A sales manager happened to be on campus yesterday and I asked him some questions regarding PWM input and subsequently programming to convert that into acceleration.  Since my PCI card only has two counters I would need additional hardware and equipment to handle all of my multichannel accelerometers.  Funding is hard to come by.  Besides that, the programming would be a nightmare for someone with no experience with this software.  However, using analog voltage outputs (which are possible with my accelerometers), the programming would be easier and more straightforward.

Long story short, I'm stuck between a rock and a hard place right now and am unsure about what my best option would be.  Considering what I have been told, I'm leaning towards changing my plans and using the analog output.  Using only my current equipment mentioned in my first post, does anyone believe that this would be my least complicated path, or should I forge ahead and attempt the PWM option?  Thanks

[garretth]

Well, your Sales Engineer is right. You will not be able to do multiple PWM accelerometers on that PCI card due to a lack of counters. Without spending any more money, I really think your best option is to set up Analog Input channels for your accelerometers. I think you will find this to be a relatively simple application. You can start with any of the analog input examples. Then just set up a Custom Scale in MAX to scale your input from voltage to acceleration. Here's a good place to start with creating scales:

http://digital.ni.com/public.nsf/allkb/0464919A11C092E386256D800079C3BB

All in all, it should be a pretty straightforward analog input application. Let me know if you have any questions about this.

[Kave Man]

I really appreciate your help in getting me to understand everything more easily, Garrett.  Don't be surprised if I'm back asking more questions when I start programming.