monitor multiple channels for analog trigger with DAQmx drivers

[DeniseN]

Hello! I would like to start a data acquisition of multiple analog channels (16) from an analog trigger. I would like trigger to monitor four of the (same) channels, and trigger when any one of them reaches a certain voltage. I found an example that would work with the Traditional DAQ drivers (using occurances), but can't figure out how to do something similar in DAQmx.

Time is also an issue, as I would like to collect the first 80 milliseconds of data after the trigger (at a rate of 500,000 Hz).

I'm using LabView 7.0 and collecting data off of two PXI-6133 cards.

Thanks for your help!

[Tom_W_[DE]]

Hi Denise-

After some research, I have found that it is not possible to use the functionality of DAQ Occurrences in DAQmx. Ironically, the reason that this functionality is available in Traditional and not DAQmx is due to the exploitation of an inherent limitation of Traditional that was upgraded in DAQmx. The multi-thread capability of DAQmx is a major advantage for most applications, but in this case it prevents the use of occurrences as they existed in Traditional DAQ.

In short, this means that you can't directly use this functionality in DAQmx. You can however emulate this functionality with minimal software analysis of the incoming signal. I have attached a modified example VI that logs data to a chart only when the analog level of one of the channels being measured has exceeded a user-defined reference value. Basically, the task is running continuously in the background but the data is not actually logged until the signal is above a predetermined "trigger" level.

Please let me know if the attached example is helpful for your application. You will see the input channels listed in the format "DevX/ai0:y" where X is the device number and y is the highest channel number of interest.

Regards,

[GriffinRU]

You can get simular results using DAQmx Wait Until Done.vi

Example attached.

Artur