LabView: multichannel Lock-In amplifier with NI 4472

[fesa4]

I woder, if someone has ever tried to implement a multichannel lock-in amplifier (LIA) in LabView. We're using a NI-4472 board, and I'm concerned about the performance: I guess, sampling all 8 channels (one as reference) and calculating the LIA takes too much time to let us acquire data with the highest scan rate.

Any suggestions?

TIA,
Felix

[DFGray]

Your performance will vary based on how fast your processor is, available RAM, etc. Check out High Channel Count Applications with the Lock-In Amplifier for some benchmarks of the 4472 with a 2.4GHz P4, 512MBytes or RAM. With that setup, they got about half full rate (54kHz) with eight channels in. The page includes links to code and other pertinent articles. Good luck!

[fesa4]

Hi!

> The page includes links to code and other pertinent articles. Good luck!

Thanks for your tip. What would be appropriate steps to increase the maximum scan rate? BTW: I wonder why NI keeps the source 'censored'?

Regards,
Felix

[DFGray]

I don't have enough experience with this code or the 4472 to give you any serious help, but I can give you places to look.

1. The code in the example I pointed to was optimized for multiple boards.  You can probably get better results in your case, since you just have one 4472, by eliminating the synchronization code.
2. Check where your bottlenecks are.  If it is processor speed, get a faster one or a dual processor (LabVIEW will take advantage of it, especially if you write parallel loops for processing).  If it is bus contention/speed, make sure other processes are not using the bus.  If it is disk speed, get a faster disk or try a RAID system.
3. Write the code so that you take advantage of LabVIEW's multi-threaded nature.  Analyze while you are acquiring using parallel loops.  I suspect the original code already does this, but I don't know.
4. If you haven't already, use the LabVIEW profiler to find your slow spots.  There are a variety of help files and tutorials on how to use it in the LabVIEW documentation.

Hopefully, someone who knows more than I do can give you some better ideas.