Why do I get errors when I use pre-trigger scans with a relatively small number of samples?

[RGA]

I have a PXI6115 (hi mem option) that I am using to collect data at 5 MHz. If I collect about 10,000 samples with 100 pretrigger scans, the acquisition works fine. However, if I collect 1000 samples with 100 pretrigger scans, I get an AI Read error. Likewise, I can collect 10 pretrigger scans with a sample size of 1000 but I get an error if I try to colelct 10 pretrigger scans with only 100 total samples.

Why is that the case?

Thanks in advance.

[Ben]

This sounds familiar.

I do not remeber the final answer, but this is what I can recomend. Use the Info-LabVIEW search engine

http://www.searchview.net/

To search fro everything posted by "Roger Hart" (sometime in the last 3 years).

I believe he posted a number of e-mails discussing what he found.

If this approach get you an answer, please summarize the results here.

Doing what I can to help,

Ben

[Ben]

In the interest of giving credit where due;

The Search engine I pointed to above was developed by Brian Renken.

It is a great resource!

Ben

[Dustin_W]

Sometimes pre-triggers scan errors are caused by a trigger comming too soon. The buffer may not have enough pretrigger data to report. This may be the case if your trigger comes less then 100 samples into your 1000 sample data acquisition.

What is the error you're getting? This would be helpful in evaluating possible causes.

Dustin W.

[RGA]

The error is 10845 and seems to indicate a bandwidth limitation.

???

[Dustin_W]

Are you currently using one of NI's shipping examples? If so, which one? If not, could I suggest trying "Acquire N - Multi-Analog Hardware Trig.vi"? This example uses a hardware analog trigger, and allows you to set the number of pretrigger scans. One added feature of this VI is that it runs in a loop and will continuously retrigger, setting the number of pretrigger scans on the fly. This would allow you to determine at which number of pre-trigger scans things begin misbehaving.

Dustin W.