synchronizing usb 6251 and 6366 boards

[sanjeeev]

Hi All,

I am new to LabVIEW and I am using USB-6251 and 6366 boards for Data Aquisition from two separate devices. I am not able to figure out a way by which I can start Aquiring signals from both the devices at the same time.

I am using the folowing block diagram..

Hi

Dev4 is the 6251 and Dev3 is 6366. It displays the output but its not synchronized.

Also can anyone suggest a way to get the outputs in any other way, I read a article with some Master/Slave triggering at the Digital interface but coudn't understand .

Thank You

[Jake_H]

Typically in synchronization you will want to share a clock and then have the events start from an event such as a digital trigger. In your application it looks like you have an AO task that you want to synch with two AI tasks from different devices. Depending on your level of synchronization and what kind of timing you decide to use, I would recommend starting with the LabVIEW shipping examples in Help » Find Examples » Hardware Input and Output » DAQmx » Synchronization » Multi-Device. Basically to get the events to start at the same time, you will need to implement a start trigger from a source such as a PFI line. You may want to refer to the M-Series Synchronization tutorial for part of your application.

[sanjeeev]

Thank You for your reply Jake.

I tried implementing that and achived partly success. Sometime sthe program runs sometimes it doesnt. I dont know why, I am using a Square Wave  of 10K Hz frequency and 5 V Amplitude as a digital trigger.attached is the VI I used for this purpose.

Sorry for the late reply.

thank You

[Jake_H]

Can you verify that your trigger is being exported correctly and on the correct PFI lines? What's your external wiring of the PFI lines? If you're program is only working some of the time then it's probably missing one of the start triggers. You'll have to verify that it's being sent correctly and that you have a high enough sample rate to capture the digital high and start the task.

[sanjeeev]

Thanks for replying Jake.

I used a scope to verify whether the trigger is being exported properly and it is getting exported and I also checked the wiring.

I found that whenever I start the prgram and then switch on/off the square wave generator, the program works fine and the trigger works fine but otherwise it fails to trigger. So each time I have to start the program then switch ON or switch OFF the square wave generator. Also this now works for all frequencies , the pk-pk amplitude of my square wave is NOT 5V as I had previously stated, I measured it as well using the scope, it is only 1.68V and this is the maximum value which my function generator can generate!!...

Also can you suggest a way of merging the two waveforms generated from the 2 DAQ's?

http://forums.ni.com/t5/LabVIEW/Merging-two-plots/m-p/1625918

Thank You

[Jake_H]

So just to clarify - the trigger source is only getting up to 1.68 V? If that's the case then your signal is being left in an indeterminate digital state. With standard TTL, a HIGH registers when the voltage crosses the 2 V threshold so if your signal is not getting above that level then the trigger will only work occasionally. If that's what your function generator is limited to then you may try an external amplifier to get your signal above that range. 

Looks like your second question was already answered!

[sanjeeev]

Thanks for your reply Jake.

I tried with another signal generating source of higher amplitude and as you said it works.:)

I was just wondering if we could generate this trigger using labVIEW on any of the Digital Output pins available on the DAQ board which can then be wired back to the PFI line. or is it like only a trigger signal generated externally can do the job?

Thank You

sanju

[Jake_H]

Glad to hear it's working. 

This signal could definitely be generated by using LabVIEW and a DAQ card. You can write a digital high to a digital line and use it as the source of the digital trigger. You will need to create a separate digital task to output your trigger.  

[sanjeeev]

Thank You very much for your guidance and advice Jeff...

I also got the digital pulse trigger..In the circuit...:):)

Thanks

Sanju

[sanjeeev]

Hi Jeff,

Now I have another situation, regarding the digital pulse, when I try to get it on the 6366 it works fine, but on 6251 its not working. It shows an error asking to specify an external clock.

Attached is the vi I am using, this is vi as I told, is working fine with 6366 as the master( which generates the trigger, a analog out and acquires as well) and 6251 as slave( only acquisition); but it fails to do the other way round.

what should I do to get the digital trigger pulse on the 6251?

Thank you

Sanju