Daqmx filling 4000 point FIFO and including pretrigger data

[jeff_scharpf]

I'm trying to acquire data at 4000 samples per second from an NI 9201 in which I set a trigger level and "arm" it (similar to a scope) and when a threshold is reached I want to end up with 4000 data points (1 second worth of data), with some pretrigger information.

I only need one analog channel.

My thought was to set up an array of 4000 points and just keep "FIFO"ing the data until the user selects "arm" at which point I wait for the threshold to be reached.Once the trigger threshold is reached, I would save one full set of 4000 points (of course with the pretrigger data, maybe 200 points or whatever)

The 9201 cannot be hardware triggered so I must do it in software.

Is there a simple way to do this? I've got some code but not sure if I need to keep the data acq task running all the time (to get my pretrigger data) or if I can just start it when the operator "arms" the software.

Looking for any advice.

Thanks,

Jeff

[KateB]

Hi Jeff,

I did the same thing for the same type of application you're doing.

Anyway, you need to start the task before trigger is armed, and keep pre-trigger data in an array.

Regards, Kate

[CharlesD]

Jeff, it sounds like you are trying to do Finite or continuous acquisition with a software trigger and some pre-sampled data to ensure that you do not miss any information due to the indeterminancy of software triggers.  If this is correct, Kate is correct, however I would just like to refer you to one of our shipping examples which does, I believe, exactly what you are trying to do.  To find this example navigate to the following: 

1. In LabVIEW --> help --> Find Examples

2. Under the browse ta: Hardware Input and Output -->  DAQmx--> Voltage -->"Cont Acq&Graph Voltage-Analog SW Trigger.vi"

This is a great shiping example that will likely do exactly what you are looking to do accomplish.