missing triggers on PCI 6052 E card

[ponnaboy]

Hi,
I'm using PCI-6052E card.I need to do triggered acquisition at 10000 scans/s from 8 channels and output 1000 points at same rate on to analog output channel simultaneously. The vi misses the very first trigger. When I press the stop button it waits for two more triggers before stoppping acquisition.

Shiv

[Filipe A.]

Hello;

I'm assuming you are talking about scan pulses, as opose to trigger pulses. A trigger pulse starts/stops the whole acquisition, while the scan pulses clocks each datapoint of the acquisition.

The problem you are seeing there, regarding that the acquisition still acquires a few datapoints after you press the stop button, is because, since you are probably using the AI Read.vi on the AI task,and because that VI is synchronous, the CPU excecution pointer will get stuck inside that VI until all datapoints of the buffer to be retrieved. So, the recognition of the Stop buttom will take place after the VI is done retrieving all points from the buffer, and that might include some extra points after you had pressed the buttom.

To accomplish that task, you wi
ll need to use a combination of counters and have digital pulses working as digital trigger/stop.

Hope this helps.
Filipe A.
Applications Engineer
National Instruments

[ponnaboy]

Filipe,
I'm doing a pre-triggered acquisition so my trigger on PFI0 is acting as a stop trigger.After each trigger the data is displayed on a chart. I wonder why does it miss(doesn't display any data on the chart) the very first trigger ? Does my trigger act as a start trigger on the very first iteration and as a stop trigger thereafter.
When I press the stop button, the while loop doesn't end because AI read is acquiring data and ideally it should just wait for one stop trigger after I press the stop button. why does it take another extra trigger to stop it ?

thanks for your help.

Shiv