missing trigger niscope

[craige]

I have a PXI chassis running Windows XP equipted with a PXI-5105 card.

I am triggering my card through a digital TTL pulse at  2Khz while attempting to acquire 500 samples per trigger at 50Ms/s. I understand that my computer cannot handle all of this data at once so i've configured NI-scope to take 2000 records before returning the values. On average I'm only seeing 1700 record sets returned per second. If I increase my pulse from 2Khz to something greater I achieve my desired 2000 records per second.

Is my card ignoring some of the triggers?

Thanks,

Craig 

[Matthew_W]

 Hi Craig,

 Can you explain in a little more detail your test setup? In particular, how are you obtaining the records/second benchmark?

 With the trigger setup the way you describe, every 500uS it will receive a trigger. When this trigger is received it will take 1 record, with a minimum record length of 500 samples.
The total records to be acquired is 2000.

 I setup a PXI-5105 triggering off a 2khz square wave on PFI1, the digitizer is set to acquire 2000 records at 500 samples per record. I timed this and it's coming in around 750mS every time. I'm attaching screenshots so you can see the setup. I've attached the example I used to this post. You will need to configure the Resource name (DAQ card), Sample Rate, Number of samples per record (minimum record length) and number of records. On the block diagram specify the Trigger source. The time readout is in mS.

The PXI-5105 should not miss a trigger if it's configured correctly.

Have a great weekend!

MatthewW
Applications Engineer
National Instruments

Message Edited by Matthew W on 08-03-2007 03:01 PM

Message Edited by Matthew W on 08-03-2007 03:02 PM

[craige]

Matthew,

Thank you for your response. I've attached a picture of my block diagram. The 'configure' and 'run' states are on two different cases in VI so I pieced them together using the awesomely powerful microsoft paint. (forgive the graphical crudeness)

So if you set up a pulse at 2Khz, how is the device returning 2000 records in well under 750ms?? It seems to me that the acquisition should at very least a second.(2000records, one for each pulse at 2Khz) Perhaps you are seeing the same thing as me because I'm averaging 1700 records per second. What am I failing to understand here? 

Thanks,

Craig

[Matthew_W]

 Hi Craig,

 What do you set your trigger rate at to achieve your desired 2000 records per second?
 Are you specifying a trigger holdoff or is that the trigger delay?
 
 Where is the records/second calculation btw? I'm curious as to how you are obtaining that value as well.
 
 Can you try running the niScope EX Multi Record Fetch More Than Available Memory example? See if it runs normally.

 I'm wondering if I miscalculated my execution time, it does not make sense to have gotten all of my 2000 records in less than 1 second either, I agree. Sorry for the confusion.

 
 Best regards,

MatthewW
Applications Engineer
National Instruments