Data Acquistion with cRIO

[Battousai]

Hello My name is Luis Amigo, and I am developing a system of acquisition of vibrations, which has the following requirements: 

a.-  Acquisition of 26 channels corresponding to non-contact displacement sensors, whose frequency of sampling must be 3000 Hz each. 

b. - Acquisition of 2 two channels corresponding to keyphasor, whose frequency of sampling must be approximately 20000 Hz. 

c. - Acquisition of 4 channels with accelerometers, with a sampling frequency of 20000 Hz. 

After quoting diverse possibilities, I selected one that have interested me. These are: 

 - cRIO 9004 (1)
 - cRIO 9102 (1)
 - cRIO 9233 (8)

Nevertheless, I have a lot of questions. 

1.-cRIO.-  The system would be formed by the controller, the chassis of 8 slot with 8 modules 9233 each.  The doubts are: 

a)  What would the sampling frequency for each channel of the system be? For a module, we know that it is of 50 kS/S, for two modules, it is of 33.3 kS/s.....  so, what would the frequency for 8 modules be? 

b) Can I set the modules to acquire at different sampling rates?  That is to say, modules of the 1st to 6th slot with a sampling rate of 3000 Hz and of the 7th and 8th with 20000 Hz

c) Can I synchronize them and how? 

d) Can I acquire multiplexing groups of modules?  That is to say, to acquire modules 1st to 4th and then modules 5th to 8th, where modules 1st to 3th and 5th to 7th would sample with 3000 Hz and modules 4th to 8th would use 20000 Hz.  If it is possible, what would the maximum sampling frequency be (considering that it would acquire only 4 modules first, and the four remainning later)

e) Modules 9233 have IEPE, which I don't need, since 28 signals of the transducers that would be acquired don't need it. Is there a way to eliminate the IEPE, for these 28 channels? 

Basically those are my doubts. I would be enormously thankful if someone could answer me or indicate me some better solution.

Greetings.

[A.S.]

Hi Luis,

I posted a response to your post at: http://forums.ni.com/ni/board/message?board.id=100&message.id=876 and I'm pasting that response below also:

1.-cRIO.-  The system would be formed by the controller, the chassis of 8 slot with 8 modules 9233 each.  The doubts are: 

a)  What would the sampling frequency for each channel of the system be? For a module, we know that it is of 50 kS/S, for two modules, it is of 33.3 kS/s.....  so, what would the frequency for 8 modules be? 

Actually, for the cRIO-9233 module, its a simultaneous input device.  Each of the 4 channels can acquire at 50 kS/s.  The cRIO-9215 can acquire at 100 kS/s/channel.  The cRIO-9221 on the other hand, have an aggregate sampling rate of 800 kS/s.  In that case, if you acquire from 1 channel, you can achieve 800 kS/s, 2 channels at 400 kS/s, 4 channels at 200 kS/s, and so on.

http://sine.ni.com/nips/cds/view/p/lang/en/nid/14164 has more information on each of these modules.

Also visit: http://zone.ni.com/devzone/conceptd.nsf/webmain/067051143608697e86256f570009762f

b) Can I set the modules to acquire at different sampling rates?  That is to say, modules of the 1st to 6th slot with a sampling rate of 3000 Hz and of the 7th and 8th with 20000 Hz

Yes, you can set these modules to acquire at different rates. Each module is configured separately.

c) Can I synchronize them and how? 

The cRIO-9233 can export its timebase for other 9233 modules to synchronize with. Its an option in the Embedded Project Manager when you are configuring your modules. This timebase can then be accessed from Property Nodes in your VI. You can even start and stop acquisition using Property Nodes.

d) Can I acquire multiplexing groups of modules?  That is to say, to acquire modules 1st to 4th and then modules 5th to 8th, where modules 1st to 3th and 5th to 7th would sample with 3000 Hz and modules 4th to 8th would use 20000 Hz.  If it is possible, what would the maximum sampling frequency be (considering that it would acquire only 4 modules first, and the four remainning later)

As I mentioned before, you can configure each module to have its own acquisition rate. The scan clock is built into each module, so they are independent. So this should be possible to do.

e) Modules 9233 have IEPE, which I don't need, since 28 signals of the transducers that would be acquired don't need it. Is there a way to eliminate the IEPE, for these 28 channels? 

As referenced in the cRIO-9233 user manual:

"The cRIO-9233 IEPE excitation current and AC coupling are always
enabled except when the module is in Transducer Electronic Data
Sheet (TEDS) mode."

All this information is available in the data sheets and the user manuals of these products.  I would highly encourage taking a look at these resources for a better understanding. I hope i was able to answer your questions.

Please let me know if you haev any other questions.