Data compression using PCI-6115

[AndrewME]

Hi,

    I'm streaming data from a PCI-6115 board and want to take advantage of the data compression capabilities of DAQmx. I've looked at the NI Developer Tools examples at http://zone.ni.com/devzone/cda/tut/p/id/4063, but this appears to be written for 8-bit samples. I'd like to use the excellent VI's linked in the Developer Tools articles but I'm not sure how to switch everything so that it will be compatible with 16-bit data (for the 12-bit samples from the 6115.) I've changed the acquisition to Raw 1D I16 from Raw 1D U8 and tried to change the data decompression VI to accomodate 16 bits instead of 8, but with no success. Any suggestions?

Thanks,

Andrew

[AndrewME]

By the way, I am using Labview 7.0...

[David L.]

Hi Andrew,

Great news – this is definitely not only for an 8 bit example. You will have no problem using it with your 6115 (12-bit, simultaneously sampled AI). The LabVIEW help for AI.RawDataCompressionType (AI Data Compression Type.JPG) lets us know that there are three types of compression: None, Lossless packing, and Lossy LSB Removal. Lossless packing will take off unused bits (I.E. – the 4 MSB’s that are discarded  because the 6115 is only 12 bits, and not 16). Lossy LSB Removal will do this, and then you can remove the lower bits as well by specifying how many bits you would like the sample to be. Please let me know if you have any further questions.