Limit Triggered Data Logging

[AndrewR]

I need to log data for 3 analog input signals. I only want to log data when a signal is present. I want to be able to aquire data for many days, and only log data a couple hours a day when there is an active signal. I need it to log data when the signal is over a certain threshold and stop when the signal drops below this threshold. I purchased VI Logger assuming this would do what I need it to do, however, when using the triggers the data cannot be exported. My card does not support hardware analog triggering. I am currently using the Waveform Scalar Limit Comparison VI. This outputs a boolean T/F when the threshold is surpassed. I am trying to use this boolean to start data logging when true. Any insight as to how this can be
done would be great. I attached a sample of what I am using for trigger detection.

[stu22]

Hi, have u tried using the software triggered data aquisition examples. These will let u configure the thresholdconditions and by adding a few little extra's for data saving and its conditions u should be able to do it this way.

Stuart

[AndrewR]

I have tried this and I am not sure If I am configuring it properly, but the VI will only log data at the exact trigger point. When the signal goes above the trigger point data stops logging.

[stu22]

Hi, i have used software triggers before and never had that happen before. What trigger are using, i presume its continuous data aquistion and multi-channel. As a suggestion u could make the trigger point a greater than or equal to point. i can only think that its to do with the slope. A probably simpler idea would be to, use a greater or equal to the point u require data aquisition and one less than that value comparison. when the data inputted is above that value, record data or go true for a case structure and when its below that value go false record nothing.

Stuart

[Filipe A.]

Andrew;

That can only be done by the use of the Conditional Retrieval Trigger. You can find Labview examples showing how that works at Search Examples->I/O Interfaces->Data Acquisition->Analog Input->Triggering an Acquisition.

Hope this helps.
Filipe A.
Applications Engineer
National Instruments

[JBomar]

I have came across the same problem mentioned above and am using the Conditional Retrieval Trigger. I can only read data through a very narrow band around the set point. I have also thought about a “greater than” comparison but the problem is, if the “Trigger Value” is wired to the ‘y’ node of this function, exactly what and how do you wire to the ‘x’ node of this function?? I would appreciate any thoughts....