long term analog signal acquire

[ofir blatt]

hi.

i got NI-USB6259 with signal express 2.0, and i need to acquire (and save to a file) 4 analog inputs at 200KHz for at least 20 seconds.

the device by itself canot acquire such mass of acquisitions.

i had a labview base software that can acquire the signals and writes the buffer contant to a file, each time it was full.

but how do i do that with signal express?  

[--Chris]

You should be able to log the data for as long as you want by using the built-in recording features.  Setup a buffered acquisition and press the record button.  It will log the signals to TDMS.  You can then view or playback the log.

[ofir blatt]

hi,

first of all, many thanks for your answer.

the problem is that the data from the buffer is writen in parallel mode (and without a continuous time vector),

insted of one time and one column for each channel.

the created file is so big that the computer crashes.

if you think i configured something worng i'll be happy if you could sent me a setup file (for the signal express)

that works.

many thenks again

ofir  

[TheWoost]

Hi Ofir,

One thing to keep in mind is that the performance you will be able to get out of this type of acquisition is system dependent.  Because you are acquiring at a fast rate on multiple channels, the buffer that DAQmx allocates in your PC memory will be filling up at a very fast rate.  Depending on your system, it would be likely that you would run into an overwrite error (DAQmx error -200279), where samples are overwritten in PC memory before they can be retrieved by DAQmx and written to file.  Ways to prevent this error are to sample at a slower rate and increase the number of samples to read (in a continuous acquisition, this is the number of samples that the DAQmx Read will retrieve from PC memory on each iteration).

In general, the TDMS format is going to be your best bet because it is a binary format and is optimized for high-speed acquisitions.  Once the acquisition has completed you can right-click on the log file and either convert it to an ASCII file or export to Excel.  There is a KnowledgeBase article here with some pointers on how to optimize SignalExpress for acquisitions such as what you are trying to do.

Regards,
Andrew W
National Instruments

[JohnV]

Hi-

I have a somewhat related question.

How can I log data in a strip chart mode and pan through the data after stopping the program?  For example, if I am acquiring data in the continuous mode at 1k and acquire 1k samples and do this for one-minute, I would like to be able to scroll back through the graph in data view and look at the data.

Also, I notice that the data view window created by the power spectrum VI has pan (the little hand) and zoom control that appear when you hover over the lower left hand corner.  How do I add these tools to my waveform graph of the analogue inputs??

[JohnV]

building on my other message, if I acquire data at 1k and acquire 1k samples I can only ever view 1 second of data.  Is there someway I can scroll back and see all of the collected data??

-John

[Phil_J1]

Hi John,

To see all the data that you have collected, in the bottom left corner of the application, you should see a Logs folder. In it should be all the logs that you've recorded. If you drag any of these into the Data View while in the Record/Monitor Mode, the whole log should be visible to you. At that point, you should be able to scroll through your data and zoom in/out of it. If you drag the output of the step that you recorded into the Data View however, it will only show you the last set of data from that output.

Regarding the "little hand" that is not available on the time viewer, we're in the process of adding it there as well. But once you manage to see you're log in the Data View, I hope you'll be able to work without it for now.

Phil

[JohnV]

Thanks Phil,

I figured that out from some of the other postings.  The old NI software tool (before Signal Express - I can't remember what it was called) actually hadled the data display nicely.

Thank-you.

PS: Will there be a new release version of SI this year?  I have v 2.5.

[Mark_E]

Hi John,

The release of new products is confidential. There are many legal (and strategic) reasons for this. Feel free to keep visiting ni.com/signalexpress and/or modify your NI profile to indicate your interest in LabVIEW news (under products and industry interests).

[sthu]

I have another question concerning this topic:
I am trying to acquire data for a long period of time and want to end up with all the data acquired from one channel in one waveform.
Using signal express I always end up with a waveform array that consists of several waveforms, that are all just the numbers of samples I specified long.
What I want to see is that the current acquisition of channel 1 is appended to the previos acquisition of channel 1. So I will be able to open the file in labview later and just have one single waveform with all the data in it. How do I do this?