Simultaneous DAQmx Tasks

[Stuart_G]

This should work.  Set up 2 tasks each which take a digital trigger.  Have one trigger on PFI0 and one trigger on PFI1.  Each of the tasks should be finite and set the samples/sec and number of samples so that you get one second worth of data.  When the first trigger occurs take a timestamp.  When the second trigger occurs take another timestamp.  Try this without the state diagram tookit to make sure the DAQ works and then incorporate the toolkit.  I am not at my computer with DAQ right now but I think you could also get the timestamp from the waveform data that is being returned.  Unbundle the waveform data to get the t0.

StuartG

[pallen]

Thanks Stuart.  I'll give that a try tonight.  

I upgraded to the latest drivers last night as well.  I believe I was running 3.5 previously. 

[pallen]

There is one problem. 

NI-USB 6008 does not have a PFI1.  

[jasonhill]

I have had some sucsess using analog triggers instead of digital.  The DAQmx start trigger function supports both analog and digital triggering.   In my case, I just set the threashold at ~.125V to prevent false triggers from my crude, hand-built trigger circuit.

Waveforms have a built in start stamp.  Just unbundle the t0 component.  I do not recall, off hand, which clock the t0 is based off of; but since you are only interested in the difference, it should not matter.

[pallen]

The analog trigger is a good idea too Jason.  But I'm a little concerned that when I'm looking at the trigging options in MAX Tasks, Analog triggering is grayed out.  So I'm wondering if this could be another limitation of the USB 6008.

I'm attaching some code.  Is this the idea?  

Thanks for the suggestion.  I'll give it a try this evening. 

[jasonhill]

Sadly, I have no experience with the USB 6008.  I can't think why you would not be able to monitor the analog channels for a trigger, though.

[pallen]

USB 6008 will not accept an analog trigger. 


I'm starting to get that, "You can't get there from here" feeling.

[Hal_L]

Hi Pallen,

The USB-6008 does not accept analog triggers and there is only 1 PFI line on this device. So you can use that trigger line to start a finite or continuous acquisition.  However, you will not be able to obtain a time between two triggers with the USB-6008. There is a great shipping example for using a hardware trigger to start an acquisition for the USB-6009 in the LabVIEW Example Finder. Go to Help >> Find Examples >> Hardware Input and Output >> DAQmx >> Analog Measurements >> Voltage >> Acq & Graph Voltage-Int Clk-Dig Start.vi. I hope you find this information helpful.

Regards,
Hal L.