HSDL on DAQ-6602 ?

[Langolier]

Is it possible to use High Speed Data Logging with my DAQ-6602 board? If not, do you have any suggestions on how increase the maximum saving frequency? Right now I am streaming at a maximum frequency of 650 kHz per channel into binary files (using 3 dma channels at once).

Thanks!

[rgharrison]

Hi Langolier,

Yes it is possible to perform high speed data logging but the speed is dependent on how many channels you are acquiring. The limitations due to the bandwidth of the PCI bus, and the way the data is packed for transport on the bus by the card, limit total bandwidth to about 2MHz. If you have more than 1 channel, this bandwidth will divide almost proportionally.

So what is your counter application? Are you performing a buffered period/frequency measurement? Anyway, if you can provide more details of your setup I might be able to give you a more accurate answer. Hope that helps. Have a good day.

Ron

[Langolier]

Hey Ron. Thanks for your response. I hope to provide you with lots of detail.

I am doing continuous buffered period measurements on 3 DMA channels at the same time. (measurements coming in from microscope). I model my 3 sources with the internal 80MHz counter, and I need my gating speed to be 660kHz. I am using a loop that reads all the buffers in parallel and then writes in parallel to binary files.

I am using a P4 2.8 gig computer with 1000Mb ram.

Right now, the program seems steady at a gating speed of about 620kHz, but this is under my quota. It works for gating speeds up to 680kHz, but these are unsteady, and they stop working after anywhere between 1 and 30 sec. Even after disabling all background windows programs, problem pers
ists.

I have looked at the HSDL and it seems a vi that reads and saves is what I need, however this HSDL vi is not compatible with my 6602 card. I'd love to use one if it worked....

Attached is my vi if you'd like to take a look at it.

Thanks so much!

[rgharrison]

Hi Langolier,

Your code looks nice and lean. As I mentioned in my previous post, you are close to the bandwidth limitations of the system (approximately 2MHz total). However, there should be errors for various types of performance issues. For example:

1) -10845 overFlowError
Because of system and/or bus-bandwidth limitations, the driver could not read data from the device fast enough to keep up with the device throughput; the onboard device memory reported an overflow error.
2) -10846 overWriteError
Your application was unable to retrieve data from the background acquisition buffer fast enough so the unretrieved data was overwritten with new data. To prevent this error, you might increase the size of the background acquisition buf
fer, increase the amount of data you read from it per call to the read function/VI, slow down your acquisition rate, or reduce the number of tasks your computer is performing.

I would suspect one of these errors is occurring. If it is the first, then it will be difficult to increase the throughput. The transfer is limited by your computer system. Reducing all bus traffic on your PCI bus might help your situation. If it is the second one, we could try increasing the buffer size. That might help achieve the rates you need. Anyway, hope that helps. Have a good day.

Ron

[Langolier]

Hey Ron.

You mentionned in your first reply to me, that it is possible to use HSDL with my DAQ-6602 device. How do I do this? The HDSL compatability list does not have my 6602 device in it, and I've tried using its sub vis and they don't work. How can I make them work with my 6602 device? Is there another version of the HSDL vi that is compatible with my 6602 device?

I ask, because the HSDL does reading from the buffer and saving in 1 single step, while my program thus far, does it in 2 steps (read buffer, write to vi) and I would like to try out the single step HDSL method to see if I have performance improvement.

I realize I am approaching the limitations of my system and the HDSL thing may not help, I would like to try a
nyway 🙂

About my error.
The error I get is:

Error -10920 occurred at Counter Read Buffer
NI-DAQ LV: One or more data points may have been lost during buffered GPCTR operations due to speed limitations of your system.

I believe this error is very similar to the errors you have mentionned.


Thanks so much, and I'm looking forward to your response!

Langolier