Multi DAQ tasks

[Qifu]

Hi All,

I want to measure temperature and voltage using two different DAQs (USB 9211 and USB 6009). The attached is my .vi file. I used two parallel loops to measure temperature and voltage, respectively. Is it a good way to do multiple-device measurement? Also, I studied several help examples, where synchronization is used. When should I use synchronization?

I am kind of new to LabVIEW measurement. Thanks in advance for your suggestions.

Bei

[TheWoost]

Hi Bei,

The way you have your VI set up is correct for doing multiple-device measurement.  A single task cannot contain multiple independent devices, so having separate task configurations for each device is the proper format for this kind of application.

Synchronization is needed when you have multiple measurements on the same device or across multiple devices that are correlated.  For example, in your case you are measuring voltage and temperature.  If you want to see the voltage that corresponds to a given temperature then synchronization is needed.  For true synchronization both the sample clock source and the start trigger of the measurements must be shared.

With the devices you are using, synchronization is not possible.  This is primarily limited by the USB-9211 because this device cannot be configured to use an external trigger or external clock.  The shipping examples for synchronization are definitely the place to start if you have devices that support synchronization (external clock and trigger sources).

Since you are new to using the NI-DAQmx API, I would also recommend referring to the getting started guide here:
Getting Started with NI-DAQmx: Main Page

I hope this answers your questions - let us know if you have any others!

Regards,
Andrew W
National Instruments

[kent.wedeking]

Hi.  I finally found a post even remotely dealing with a problem i'm having.  i'm trying to acquire data more or less simultaneously on multiple modules on a CompactDAQ setup, specifically NI-9203 (AI current) and NI-9211 (AI thermocouple) modules.  I can acquire just fine when reading only the current or temperature data.  when i try to do them together, they get extemely slow.  I'm not so much concerned about synchronizing them so the temperature corresponds.  I do however at some point in my program needs to be able to output via a NI-9265 (AO 4-20 mA) and read the AI current and thermocouple modules together, preferrably around 20Hz.  I can't get anywhere near this right now.

Right now I have one task setting up and running my collection of channels (16 AI current and 8 AI thermocouple).  Is there a better way to do this, and am I just up the crick?

Thanks,

Kent

[KyleBryson]

Hi Kent,

You should definitely be able to acquire channels from both an NI 9203 and an NI 9211 in the same chassis in a single task, and run an AO generation at the same time.  Can you upload your VI, or a screenshot of the block diagram?  That should help us make sure that your loop is structured correctly for maximum performance.

Regards,
Kyle

[kent.wedeking]

Kyle,

I think i got it figured out.  my coop (who worked as an AE for NI last summer) hooked me up with how to properly use DAQ-mx yesterday.  I had to talk with an AE this morning because I couldn't get my loops run very fast.  ended up having to go with hardware timing.  guess that's what i get for being a lowly mechanical engineering trying to learn data acquisition ... thanks for the help ... later ...