11-16-2005 10:28 AM
11-17-2005 06:04 PM
11-21-2005 10:24 AM
Ryan,
Hi, thanks so much for answering my post. I now have a better understanding of the bench mark graph on page E-8 of the DAQ 653x User's Manual. Correct me if I'm wrong but the Buffer Size the User's Manual mentions is located on the computer's memory. If you wanted to capture more than 32MB of data, which is the size of the buffer on the card, then you would have to operate in the Pattern-Input Continuous mode which requires that the data be DMA to the computer. In this mode you are capable of capturing 1GB of data, but the number of bits you sample depends on the rate you want to sample. I'm just going over this stuff to make sure I have a clear understanding. So back to capturing 1GB of data, if the rate of the data was coming into the card a 20MS/sec then to capture the data without dropping samples you would have to only sample 8-bits. If you try to capture 32-bits you could only sample the data at 5MS/sec. Am I correct on my thinking? I will look over the manual one more time, but doesn't the card have a fixed sample rate, it's always sampling at 20MS/sec? Ryan, one more questions, in you first reply you said that capturing 1,048, 576 samples would only capture 0.05 seconds of data, is that the max time I can capture, or is that the max sample of the driver?
Thanks for all you help,
joe
11-21-2005 10:45 AM
Ryan,
Hi, I've spoken with the design engineers and they have decided to buffer up 4-seconds of data on an external card they are designing and then send the 32-bit data to the NI 6534 card at 5Mhz, how's that sound?
thanks,
joe
11-21-2005 11:01 AM
11-23-2005 09:07 AM
11-29-2005 02:06 PM
11-29-2005 04:38 PM
11-29-2005 05:20 PM
Ryan,
Hi, the user wants to do an FFT on the data. The incoming data is a 32-bit word consisting of two words of data, a data word in the upper 16-bits and a data word in the lower 16-bits. I had planned on capturing the samples to computer memory, separating the data, and then saving it to a file. I only need to run this sequence once, but need buffer up 4-seconds of continuous data. The user will then open the file and do whatever analysis he wants to do. I've written my application using the traditional DAQ drivers, also it is basically a sequence structure, first configure the DIO vi, read a large number of scans to computer memory, process the data (separating the data into 16 bit chunks), and then saving the data to a file, and then I'm done until the user hits the start button to do the process again. Sounds simple but the only problem is that I'm capturing a ton of samples. How's that sound?
thanks,
joe
11-30-2005 09:24 AM
If you haven't done so yet, I would recommend you read the tutorial Managing Large Data Sets in LbVIEW. This will help with keeping copies to a minimum. One word of caution, however. You will not be able to store more than about 1.5GBytes of data in memory using Windows XP due to OS limitations. If you store your data in one array, you will not be able to store more than about 1GByte in LV7.1, about 800MBytes in LV8.0, due to memory fragmentation issues. Maximum theoretical memory use on any platform is 2GBytes, since LabVIEW uses signed 32-bit integers for memory pointers.
I would also recommend you use NI-HWS to store your data. It can be found on the driver CD under the computer based instruments (it is the default file exchange mechanism for their soft front panels). This is a fast binary format based on HDF5 that includes compression, should you wish to use it. Most analysis packages (MathCAD, Matlab, Mathematica) will read HDF5 files, so you should not have any problems there.
Good luck! Keep us informed. If you have any more problems, let us know.