Can I skip "Done state" in high speed digitizers?

[Vegge]

We are trying to retrieve data from a USB-5132 device, with a sample frequency of 25MS/s. Our record length is 6000 samples and we have an external digital trigger with a frequency of at least 120 Hz and we need 120 records.

We have a labview program, but somehow it only lets us retrieve the data at a frequency around 60 Hz, probably because of the USB to computer interface. Is it possible to increase this?

Alternatively we have considered the state diagram of the unit, and observed that the "Done" state waits for the computer to intervene. Is it possible to skip the "Done" state, and store the 120 records on the onboard memory and extract all the data at the end?

Regards

Jesper & Anders

Message Edited by Vegge on 10-29-2009 07:10 AM

[Vegge]

PS. We forgot to mention that we are using the NI-SCOPE Express component in Labview to configure the device.

[Morini]

Hi Jesper and Anders,

The USB scopes such as the 5132/3 do not have continous acquisition or multi record acquisition. That means you have to use software timing to acquire data at 120Hz, which gives us a digitizer trigger rearm time of 8.33ms.

The rearm time is the time it takes to stop the acquisition and then start the acquisition after each trigger. This means that fr USB Scops the rearm time is software dependant and non deterministic. I cant give you the exact rearm times(System dependent) but I would say it would be in the hundred millisecond range roughly.

I'm not sure that you can implement a software workaround to achieve a rearm time of <10ms. You can try to free up as much CPU resources to Labview by closing all none needed background applications. With a fast computer you might be able to reach a faster rearm time. But the recommended solution is to choose a Hardware solution, where the digitizier supports "Multi Record Acquisition".

Our other digitizers such as the NI 5105/5114/5122/5124/5142/5152/5153/5154/5622, support multi record acquisition and have a rearm time specified in the micro second range. This is calculated (500 ns + posttrigger storage time) and the 100 ¼s holdoff time. This would be recommended because the rearm time is hardware dependent unlike the USB scope.

Rearm time for a 5622 scope: http://digital.ni.com/public.nsf/allkb/99B4AFB631CD5DAF8625761F00777FB5?OpenDocument

I hope this helps!

Thanks!

Message Edited by Morini on 10-30-2009 02:02 PM

[Vegge]

Thank you for your fast response