6259 External Trigger Frequency Gap

[Sousuke]

Hello,

I have a curiosity in using an external trigger.

I am currently using a PXI-6259 in a PXI-1031. I am using a function generator (HP 8116A) as an external trigger. The sign wave from the function generator’s output is conditioned using a comparator and as far as I can tell using both a digital and analog oscilloscope the signal is clean. I am sweeping the frequency of my trigger from 10kHz to 60kHz. I have also used the trigger output from the function generator with no change in my issue.

The curiosity comes in around 45kHz. There is a very narrow range around 45kHz where I receive the following error:

“Error-200019 occurred at DAQ Assistant” “

ADC conversion attempted before the prior conversion was complete. Increase the period between ADC conversions. If you are using an external clock, check your signal for the presence of noise or glitches.”

I can’t come up with a reason why a clean waveform (assumption that it is clean) would have this issue at a specific frequency. Any ideas?

-Sousuke

[Ever_Song · Accepted solution]

Hi Sousuke,

This error is caused by the sample clock exceeding the conversion rate of the ADC. Here and here are a couple of Knowledge Bases that address this error.

Also, it would be helpful to know more information about your setup. How are you connecting your function generator to the 6259? Is the function generator supposed to be a retriggerable external trigger or an external time-base or are you using it to gate something on the card?

[Sousuke]

Bill,

Thank you. I didn't realize that this error could be caused by a buffer size issue related to the rate specified in the task configuration. I was under the assumption that this error was only caused by noise in your signal, causing a second trigger too soon after the first one, exceeding the conversion rate.

I understand how the buffer size would create a cutoff for the trigger frequency as an upper limit, but I find it interesting that in my case there was only a small window. I was sampling out to 60kHz with no issue yet at 45kHz I would receive this error.

Even though the issue was this buffer size, I'll provide a little information about my system incase it turns out to be helpful. I was using the default 1kHz rate specified in the task configuration. The function generator's trigger output (a digital 0-5V signal) as the external trigger. The function generator was directly connected to the 6259 in this setup. The only variable I was tuning a at the time was the frequency of the clock.

Anyway, increasing my buffer fixed the issue. Thanks for the help.

-Sousuke