PCI 6120 and USB 6251

[annayaj]

I am interested in purchasing a DAQ system for acquisition of RF signals.  My requirements are two channels, though four is preferable and 16 bit.  The system must be portable.  I will use a laptop.  If it’s pci I plan on using a pci enclosure (Magma).  The signals of interest are from 10 kHz to 400 kHz.  I want to sample continuously for up to 10 minutes.  I’m a novice so I apologize for any omissions or mistakes.

I’m interested in the PCI 6120 and the USB 6251.  

My questions are:

6120

1. The data sheet specifies an 800 Ks/s rate with NI-Dax and 1 Ms/s rate ‘with additional download’.  What is the additional download?  I will do post processing using Matlab so I would need a binary file for the results.  I’m assuming that this is how the data are saved.  What advantages are there to using NI-Dax?
2. Is the spec for 800 Ks/s or 1 Ms/s per channel or for all four channels combined?
3. Will the 6120 stream data to the PC hard disk or memory?

6251

1. The data sheet specifies 1.25 Ms/s single channel, 1 Ms/s aggregate.  Does this mean that a single channel acquires data at 1.25 Ms/s but all 16 channels will acquire data at a combined 1 Ms/s, so about 62.5 Ks/s per channel?
2. Does the 6251 require an additional BNC module or am I better served by the 6251 BNC.  It looks as though the 6251 BNC would serve my needs.
3. Referring to question 3 for the 6120, how is streaming performance over USB for the 6521 BNC?  Are my requirements easily fulfilled by the 6521 BNC?

Any other suggestions for equipment from NI would be most appreciated.

Thanks in advance.

[Mark_E]

Hi annayaj!

Let me try to answer your questions as best I can.

The PCI-6120 card is known as an "S-series" card, meaning simultaneous sampling. So the spec is for each channel. The additional download can be tricky to use, but possible. DAQmx is the driver used and there are many advantages. Learn more here. The data are saved in a few different formats, such as text, binary, or a combination of the two as .tdms files. You would need to specify if you want the data saved, otherwise it goes into system memory and is displayed and then lost. There are many examples built in to LabVIEW and other programs.

The aggregate spec of 1 MS/s of the USB-6251 is the combined rate for all the channels used. So if you only use 4 channels, then they each could sample up to 250 kS/s. Do you need only BNC connections or would you possibly use other connections? But from Nyquist theory alone, if you are inputting a signal of 400kHz, you need at least double that rate to detect its frequency, so one of these devices would be needed for every such signal.

Instead of using the PCI-6120 with a magma case, I suggest a PXI chassis with 2 PXI-6251 cards now and room for 2 in the future. These could be terminated with a BNC block connector if needed, like the BNC 2110. The combined price of the PXI chassis with 2 cards would be less expensive than the PCI-6120 card alone.

For more detailed sales questions, I recommend you speak with a sales representative. You can do that by visiting www.ni.com/contact.