using buffer on 6115 card, save the data without losing

[aggie2006]

Hello

My name is Chris, working at the Texas A&M University.

I’m a novice LabView user.

Right now, we tried to save data as many as possible.

We used to use the PCI 6111 and 6110 Daq card and we found that there’s some missing data. So we purchase PCI 6115 (have a buffer).

We tried several program NI suggest (like example vi), however we still have a problem saving data. 

In the condition of “5MHz sampling rate” and “100000 (0.1M) number of samples”, we saved the data.  When we checked the data, we can see that every 100000 point the data start again. (attached picture – you can see the data around at 1x10^5).  Even we change the number of samples into small number like 5000, 3000 and etc, we can see the same result. We want to save the data without any lost.

Some one said if we use the buffer in the PCI 6115, we can save the data without losing. 

So, could you tell me what’s the problem and how can we solve this?

I also have a couple of question.

1. How many bytes per samples we can save with PCI 6115?
2. Using the memory (buffer) on PCI 6115, how can we control to send the data from buffer on the 6115 board to the hard driver in the computer?
3. Using the memory (buffer) on PCI 6115, how much fast buffer on the 6115 board to the hard driver in the computer?
4. If we save the data in binary format, is it much faster? 

Maybe some of my question is not right.   Please understand my ability is not that good.

Please give me any advice and suggestion about this matter.

Thank you in advance.

Best regards

[stilly32]

Hi Chris,

It looks like you're importing the data into another program, do you still see the missing samples in LabVIEW? How are you setting up this acquisition, are you doing finite acquisition in a loop, or continuous? Also, do you see the behavior at different sampling rates? Also, I would remove any processing from your acquisitions loop, and do it during post acquisition.

In response to your questions:

1. I'm not sure what you mean by "how many bytes per sample" - your card has 32 or 64 MB of on board memory, but it won't wait to fill up before it transfers over, that will be handled by the driver.

2. The driver handles the transfer for you, this does not sound like a case where changing the buffer size will result in less signal loss.

3. I'm not sure if I understand this question either. Data will go from the onboard memory into system memory and is limited by the PCI bus (~100 MB/s practical). It won't go to the hard drive until you write it to file, or unless you exceed your system memory.

4. Saving to binary is recommended for streaming data. Also, in 8.20 we introduced TDMS files which are also great for streaming to disk.

Hope this helps,

Andrew S.

National Instruments