06-23-2009 02:11 AM
Hi,
I have three signals (ai0, ai1 and ai2) at 6000 samples at a data rate of 25k. ai0 is a trigger signal and reaches an amplitude of 4V the other two (ai1 and ai2) occur about 10ms after ai0 and do not exceed 0.2V.
I am trying to record ai1 and ai2 using a software trigger and a pre-trigger of 2000 samples as a reference point.
I select the, "run" (-->) button and when the system is triggered, the desired graph is observed for a split second but the .txt file(s) output show only the signal shortly after the signal has passed, this happens about 50% of the time.
When the desired signal does fall within the window, it does not have a set reference point. This all seems to be the one problem regarding the, "run" button not reading with respect to ai0 but erratically around it.
I am a university student working with LabView for the first time for my thesis, please let me know if there is any more information I can provide.
Regards
Kumaresan.S
06-23-2009 02:53 AM
Kumaresan,
please post your current vi(s) and tell us which hardware you are using.
I'd say that you either have a timing issue or a race condition of some sort...
Norbert
06-23-2009 03:29 AM
06-23-2009 08:20 PM
I'm using LabVIEW 2.0.0 for a really straightforward task and the issue apperars to be simply that I was not inputting the triggered data to the "Save ASCII/LVM" - I am now getting the expected plots consistently.
Problem solved (? Cautiously)
I will elaborate what I am doing for the record; the event I am recording ~10 instances of a single discrete event which occurs for ~40ms every 35 seconds. Initialising the system. Forgive my naivete but I was not aware that a loop was possible or necessary in my case - the use of LabVIEW is not the focus but simply a means to an end.
The Steps being used are "DAQmx Acquire" - "Software Trigger" - "Save ASCII/LVM". The physical device to which the signals arrive at before the computer is a National Instruments BNC-2110 "Analog I/O" and "Digital & Timing I/O" panel.
The "split second" after appears to only have been the random variation in position of the raw input which explains why the signal would not keep a constant reference point.
I truly appreciate your immediate responses.
Thanks and regards,
Kumaresan.S
06-24-2009 12:43 AM
Are you really using LabVIEW 2.0? If so, I think you are long overdue for an upgrade.
I don't think you are using LV2 because DAQmx wouldn't be able to work with it.
06-24-2009 01:26 AM
I don't think you are using LV2 because DAQmx wouldn't be able to work with it.
I too think so
06-24-2009 09:46 PM
No, I triple checked the version - it's 2.0, this computer is ancient and has been in the lab for what I believe would be about a decade. The first step I use is "DAQmx Acquire: Analog Input".
06-24-2009 10:24 PM
Could you be using Signal Express 2.0???
Please upload your VI. Also, attach a screenshot of your VI has a .png or .jpg.