Delayed acquisition after start trigger on 6542

[02Fede69]

Hi all,

I'm trying to acquire a single digital waveform with a start trigger by using a PXI 6542 board.

The trigger I can use arrives 30 msec before my data burst (data burst width = 50 msec).

My sampling rate is high and my on board memory is low.

I need to sample my channel  at least 20 msec after the trigger.

How can I do that?

Thank you

Federico

[Zador]

I had to do something similar a few days ago, with different hardware. You can configure delayed triggered acquisition using DAQmx. What I did was add Start.Delay property to DAQmx Start Trigger (Digital Edge).VI, see attached. You can set the delay in clock cycles or seconds. Note that you can not have a zero delay (took me some work to realize this), it must be at least 2 clock ticks.

[John_P1]

Hi guys,

The 6542 actually uses our HSDIO driver, so it does not have the same properties available that a DAQmx device would.

Unfortunately, the Data Delay property of HSDIO only allows for fractional sample clock delays (you cannot delay for nearly long enough).  A couple solutions I can think of that might work out for you:

1)  Trigger the acquisition off of your data rather than the trigger signal (you can use a reference trigger to acquire pre-trigger samples).  If there is a known signal on your lines you could try a Pattern Match Reference trigger.

2)  Pull samples off of the card as they are coming in so you do not run out of on-board memory.  You might want to check out the following streaming example: NI-HSDIO Stream to Disk

 

Best Regards,

John

[Keith.Shapiro]

Hi Frederico,

How many channels are you acquiring on?  And are you acquiring using onboard clock or are you using Strobe?

Thanks,

Keith Shapiro

National Instruments R&D