Please help in configuring my system

[Kumar Manohar]

Hi,

I am looking for a NI based system with two input channel with bandwidth of my signal 200MHz max and I would like to take two channel input from my sample and would like to do the cross spectrum of the signal comming from two channel.Describing the scheme in detail. There would be two channel out from the sample.Each channel to digitize the signal in real time and do the cross spectrum. A/D to have atleast 10 bit resolution and do the FFT (1024 points ) and cross spectrum multiplication of the signal (100KHz-200MHz bandwidth)and 1000 averaging of such cross spectrum in 10s or less.

I am just confuse with the bus communication from the A/D to the processor will not take the load of all data. accroding to my calculation each second I would be needing 800MBps bus to do the real time data transfer to the PXI controller or computer processor and PCI compact or PXI bus would be not able to handle this traffic. How to design the real time measurement scheme without using down conversion scheme.

Please help.

Thanks in advance

Manohar

[ninlmartijn]

Dear Mr. Manohar,

Thank you so much for your post on our discussion forum.

It is indeed not possible to write this amount of data through a PXI bus. Most digitizers have a onboard memory (and are available with different memory sizes). The idea is to sample for a period (memory size decides how long you sampling period is). The memory will be stored in the onboard memory, and from there it will be transported to harddisk. I found some information about this topic under this link.

There is also PXI express hardware available. Besides the higher transfer rate, the PXI express bus gives you the advantage that the bandwidth isn't shared wit other devices on the bus. There aren't a lot PXI express cards available at this moment, but there will be in the near future. For PXI express there is a PXI express chassis with conventional PXI slots, PXI express slots and Hybrid slots. For this configuration a PXI express controller is needed. We have a RAID data storage available for fast data streaming.

With these kind of systems it is best to get in touch with one of our Field Engineers. Maybe I'm wrong, but I thought we had emailed (about another topic) earlier this week. If that is the case; please send me a email and I will get you in touch with the right Field engineer. Also for other questions; please don't hesitate to contact me.

Best regards,

[Kumar Manohar]

Dear Martijn S,

I was in touch with Arnod from NI and I already explained to him our problem. I was just looking at your website and found that PXI express card have bus speed over 1GB/s. So why it is not possible to have that to implement in our system. Do the PXI chasis have PXI express bus speed and deginated to each slot seperately or they have shared bus scheme there? Lastly, my querry is that what would be max bus speed I could get with MXI (optical decoupler)express card to decouple  my computer with measurement setup. I am looking into the prossible mixed scheme of using RAID controller(Which is not possible to have it for real time case but might be for the storing the data simultaneously ) and dead time of data aquistiion(when we are considering for real time data aquistion). I will come back to it as soon asI have concrete design with me.

Looking forward for your help.

With best regards,

[ninlmartijn]

Dear Mr. Manohar,

Thank you for your respond. Please be aware that PXIexpress cards are different from PXI cards. When selecting hardware please look at PXI express hardware, it is like PCI and PCI express. With PCI /PXI you have a shared bandwidth, wit PCI express / PXI express the bandwidth designated.

The PXI express is another type of slot, you need a PXI chassis with PXI express support. Mostly those type of chassis have the three type of slots I described earlier. Those chassis will need a PXIexpress controller or a MXI link with PXI express. The PXI bus and PXI express bus are separated from each other.

If the PXIexpress card meets your requirements it's easy to configure a PXI system based on PXI express ( www.ni.com/advisors ). I would be happy to help with the system configuration.

Best regards,