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PCI-6251 - Acquisition sur disque dur

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Bonjour,

 

J'ai acquis une carte PCI d'acquisition Multifonction modèle PCI-6251.

 

J'aimerai savoir dans un premier temps comment connecter un disque dur directement sur cette carte, et quelles doivent être les caractéristiques de ce disque dur en terme de taille, de vitesse de rotation et de mémoire cache.

De là, quelles sont les configurations logicielles permettant l'acquisition d'une dixaine de voies analogiques directement sur le disque dur? Peut-on lancer l'enregistrement des voies sur disque dur à partir de Labview? Et comment les réccupérer?

Enfin j'aimerais savoir quelles performances je pourrais atteindre en terme de nombre d'échantillons enregistrables et de fréquence d'acquisition.

 

Je vous remercie d'avance.

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French to English for more and fast responses

 

 

Hello, 
I purchased a PCI acquisition Multifunction Model PCI-6251. 

I would like to know at first how to connect a hard drive directly onto the card, and what should be the characteristics of this hard drive in terms of size, speed and cache.

Hence, what are the software configuration used to acquire about ten analog channels directly on the hard drive? Can we start recording channels on disk drive from Labview? And how réccupérer?

Finally I would like to know what performance I could achieve in terms of number of recorded samples and frequency acquisition. 

Thank you in advance.
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Hi,

you can't connect directly the 6251 to an HDD, you need a device with USB hosting capability, such as a PC.

 

Just install the latest version of DAQmx on your PC, and use the DAQ assistant (on block diagram, signalexpress, then acquire signals, then DAQ assistant): the wizard is easy and user-friendly.

 

I believe a standard 7200rpm, 16MB buffer HDD will do (write capability under Win XP is about 80MB/s)

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Accepted by topic author TchipyNioc

Hi all,

 

xdaf is correct that you will need a PC host to communicate with the 6251.  The 6251 can acquire analog inputs at 1 MHz multiplexed (for 10 channels this would be 100 kHz per channel), so you will probably not run into any problems at these rates simply using the DAQ Assistant like xdaf mentioned.  Having said this, I wanted to take some time to more thoroughly address the following question:

 

Q:  "Hence, what are the software configuration used to acquire about ten analog channels directly on the hard drive?"

 

A:   DAQmx 9.0 introduced a very cool feature called DAQmx Logging that will allow you to easily optimize your streaming to disk.  You can read more about it in the link provided, but essentially this feature allows you to directly write to your hard drive from the DMA buffer without going through application memory.  Comparing the two methods:

Old Method:  On-board FIFO >> DMA Buffer >> LabVIEW Memory >> DMA Buffer >> Hard Drive

 

New Method:  On-board FIFO >> DMA Buffer >> Hard Drive

 

The new method will use minimal CPU since all transfers are accomplished by DMA.  The result is a binary TDMS file (2 Bytes per sample on a 16-bit card) that can be viewed with the TDMS viewer or brought into LabVIEW for analysis.  The header of the file stores calibration and scaling information.  If you need to integrate this file with other software, the following link has more information:  Integrating TDMS in Third-Party Programs

 

You also have the option if you want to bring the data into LabVIEW for immediate viewing/processing.

 

I should also probably add that the 1.2 GB benchmark mentioned in the DAQmx Logging Article would require a faster bus and hard drive configuration.  We used two 2x 8164 Raid Arrays in conjunction with a PXIe chassis full of simultaneous cards.  The 80 MB/s that xdaf mentioned is on par with some faster hard drives and is close to the practical limit of PCI bus throughput.  This is probably just extra information, since the data coming off of your PCI 6251 will be nowhere near this limit.

 

Even though the streaming rates required to acquire from a single PCI 6251 should not be too demanding, I suggest looking into the new feature of DAQmx 9.0 to simplify your data logging, optimize the code, and allow for fast streaming to disk with minimal CPU usage.  I hope this was helpful!

 

 

Best Regards,

John

 

 

P.S.  Once DAQmx 9.0 is installed, several examples can be found from LabVIEW under Help >> Find Examples... >> DAQmx >> Analog Measurements >> Voltage >> TDMS Streaming ... .vi

Message Edited by John P on 09-15-2009 12:20 PM
John Passiak
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Hi,

 

Thanks a lot for your replys, I'll try these methods.

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