Do NI cards actually meet their specs?

[Azazel]

Hello all,

This is a question concerning the S-series Daq cards, inparticular the 6115.  According to the specs they say they can acquire 4 channels at 10MHz simultaneously.  I can only get my card to aquire at 9.2MHz which is very annoying.  My second problem is that when I use and external trigger (which I need to do for my application) I can still only acquire at 9.2MHz but the card does not want to acquire at this speed for both of my A-inputs but seems to be splitting the clock speed in half...therefore only giving me a sampling rate of approx.4.6MHz per channel.  Is there something I am missing here?  Has anyone else noticed this with their DAQ cards? I am using XP, labview 7.1, PCI-6115 with a 2110 BNC box.

Azazal

[AlanArmstead]

Hello Azazel,
I'd like to ask you some questions if I could:
1) Are you using an external clock, or internal?
2) Are you doing a finite or continuous acquisition?
3) You mentioned that the sample rate is cut in half when you sample two channels.  This certainly should not happen, how are you verifying this behavior?
It is also important to mention that that 10M Samples per second on 4 channels with 16 bit data is 80 MB/sec worth of data.  This is a lot of data to manage.  Are you going to be writing to disk, or just displaying the data?  You will probably want to consider reading raw or unscaled data.
-Alan A.

[Azazel]

Hello Alan,

1)I am using a 10 MHz external clock which consists of of a bursted signal of 300cycles which is triggered off of a 13KHz sine wave.  So at the beginning of each rising edge of the sine wave I externally trigger a function generator to produce 300 cycles of a square wave at 10MHz (currently the card only lets me use a 9.2MHz square wave), which is sent to the DAQ card for data acquisition.
2)Right now I am using continuous....does this make a difference?
3)I have verified this behaviour by taking only 300 samples in my vi, and that only produces 150 samples for each of my 2 Analogue input channels. 
4)As far as the data goes, I am using this data to produce a medical image, kind of like in an ultrasound imaging system.  If the card will sample correctly at 10MHz for each channel I require about 2 Ms per channel.  I would take the data....do a calculation with the data and display.  I would also need to save the data from time to time as an I16 file for post processing.

I am unfamiliar with reading raw or unscaled data....what does this mean? I have read on other threads that by using DAQ-mx this slows down the speed of everything...is this true?  I have attached my base code for you too look at (if you have time).  There is a sub vi in this code but for the data acquisition it is not important as it is the calculation part of my code.  Maybe it would help if you viewed it as I might have done something wrong to cause my sampling error.  Just wanted to say thanks for the help in advance:)

Azazal

[AlanArmstead]

Hello Azazel,

I'm not exactly sure what's going on.  Maybe we could troubleshoot this via email.  Would you be willing to post your email, so I can email you directly?

-Alan A.

[Azazel]

That would be great!  You can reach me at beau.standish@gmail.com.  I also have another question, I am trying to use an external clock and have hooked up my bursted 9.2MHz signal from my externally triggered function generator to pin PFI7 on my BNC-2110 board.  Then it struck me.....can I hook up this analogue input to the digital terminal. I don't think I have a good understanding on how to externally trigger this 6115 card.  Thanks again for all of your help and your continuing help.

Azazal