Continuous Acq using PXI 6552

[Michael Collins]

Hi Chris,

Yes I understand where you are coming from and that makes sense.  However I still think the I/O card is limited for my application.  While using the onboard sample clock, I was hoping that the acquisition and generation rates could be different.  I require to generate a signal at 20MHz but only acquire at 1MHz, while having no discontinuities in the generation signal.  I've ammened my original document with loop of 4 cycles shown.  In my final solution, I wish to have 1M of such cycles, again with no discontinuities.  The plan was that I could use the scripting software to take one cycles and place a repeat statement around it for a loop of 1M etc.  But if I cannot use different rates for generation and acquisition I'll exceed my acquisition memory size at 8M.  So the only option I see available is to upgrade to a card with 64M memory, and readback on every generation clock

sample and delete much of the redundant data?

Is there any work around with my 8M card.  I hope I am making this issue clear and maybe I am missing something?

Thanks for your continued support.

Regards,

Michael

[Ana P]

Hi Michael,

The onboard sample clock controls the rate for acquisition and generation of the samples, so the work around would be trying to generate the trigger signal at 1 MHz to read the data while generating at 20 MHz. I want to be clear in what you are trying to accomplish, so I can try to reproduce it at my end. Do you want to read one sample every 20 clock cycles or 5 samples? I understand that the main problem is that when you get the trigger pulse you are reading data only on the first trigger mark, but you want to generate 1 M pulses to acquire one sample with every pulse. If my assumptions are mistaken, please let me know.

[Michael Collins]

Hi,

Yes generating at 20MHz while reading the data at 1MHz is the ideal situation.  Yes I wish to read one sample every 20 clock cycles.

So at the end I have 1M samples in total.  So yes generating 1M pulses to acquired one sample with every pulse is exactly what I

want to do.  Like I have mentioned before though there cannot be any discontinuities (stops starts) in the generated 20MHz clock.

Regards,

Michael

[Ana P]

Hi Michael,

Instead of generating the 1 MHz signal using markers, we could use one of the digital lines to generate that signal and use it as the sample clock for the acquisition. I’m attaching the modified example where we use the 20 MHz onboard clock for generation and generate a 1 MHz signal for the acquisition sample clock in digital line 1. I hope this helps for your application,

Message Edited by Ana P on 05-19-2008 08:44 AM

[Michael Collins]

Hi,

Could you save that as 8.2 version and re-send please.

Thanks,

Mike

[Ana P]

Hi Michael,

Here it is in version 8.2. Regards,

[Michael Collins]

Hi,

I'm getting an error as follows.......

Possible reason(s):
Driver Status:  (Hex 0xBFFA49B5) DAQmx Error -200586 occurred:
Measurements: Hardware clocking error occurred.

If you are using an external sample clock, make sure it is connected and within specifications.  If you are generating your sample clock internally, please contact National Instruments Technical Support.

Device:  Dev1

Status Code: -200586

[Ana P]

Hi Michael,

In this program I’m generating the 20 MHz signal in digital line 0 and the 1 MHz signal in digital line 1. I’m using this last signal as the sample clock for the acquisition task. In order to do that I physically connected the digital line 1 to the Strobe pin of the card. So I start the generation task and then the acquisition task (that uses the previously generated signal as a clock). I understand that is the reason why this error is showing up, you will need to physically connect digital line 1 to the Strobe. I’m sorry for not explaining this in details previously. I hope this help,

[Michael Collins]

Hi

I should have spotted that myself!  Thanks for you patience with this issue.  Much appreciated. 

Regards,

Michael