Write to File with Multiple NI and MCC DAQs

[PB21]

Hello,

I have multiple DAQs (from both NI and Omega) each collecting data on multiple channels from a variety of sensors. I want to log all the data from all the daqs in the same excel file. I tried merging all the data signals and feeding the merged signal into a "Write to Measurement File" in its own while loop, but the excel file generated only has one column of data and no header describing which daq the data came from or even what type of signal it is. Also, the excel file is only generated when I first open and run the .vi. If I run it again, it doesn't update the file.

The daqs I'm using are:

--One NI USB-6008 (voltage)

--Two NI 9211 (thermocouples)

--One OM-USB-TC-AI (thermocouple and voltage)

How can I log all of their signals in one file?

Also, how can I have all of the daqs on the same clock? The NI daqs use DAQmx while the MCC daq needs ULx .vis. I can't connect them to the same clock.

I attached my .vi file and a pdf of the block diagram.

Thanks very much.

[GerdW · Accepted solution]

Hi PB,

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@PB21 wrote:

The daqs I'm using are:

--One NI USB-6008 (voltage)

--Two NI 9211 (thermocouples)

--One OM-USB-TC-AI (thermocouple and voltage)

How can I log all of their signals in one file?

Also, how can I have all of the daqs on the same clock? The NI daqs use DAQmx while the MCC daq needs ULx .vis. I can't connect them to the same clock.

---

They all support to output waveform from their Read functions (DAQmx or ULx)! You just need to build an array from those waveforms and save that array to a file. I recommend to use TDMS instead of ExpressVIs and "Excel"…

Those devices cannot share the "same clock"! The USB6008 is a rather cheap device, supporting only an external start trigger. How do you connect those NI9211 modules? AFAIK they also don't support external clocks. And that Omega/MCCDaq device is a player on its own, as NI-DAQmx doesn't support 3rd party devices…

[PB21]

Dear GerdW,

Thanks very much for your help! I really appreciate it.

As per your suggestion, I was able to build an array with all my signals and write it to a TDMS file. Thanks for the tip!

I'm connecting all 4 of my DAQs to my computer using a USB 2.0 4-port hub.

I have all the DAQmx VIs connected to the "OnboardClock", but the ULx VIs can't. As you can see in this screenshot of my TDMS file, the Omega/MCC signals have an entirely different start time than the NI DAQ signals. And even the NI DAQ start times are off by a few milliseconds. Do you have any suggestions for how I can make the start times line up?

Thanks,

Paige 

[GerdW]

Hi Paige,

---

@PB21 wrote:

I'm connecting all 4 of my DAQs to my computer using a USB 2.0 4-port hub.

I have all the DAQmx VIs connected to the "OnboardClock", but the ULx VIs can't. As you can see in this screenshot of my TDMS file, the Omega/MCC signals have an entirely different start time than the NI DAQ signals. And even the NI DAQ start times are off by a few milliseconds. Do you have any suggestions for how I can make the start times line up?

---

To have those devices all start at the same time you would need to synchronize them or to use a start trigger for all of them.

As said before: syncing capapbilities might be quite limited with your rather cheap devices…

I know for sure the USB6008 only supports an external start trigger: do your other devices support such a trigger signal?

When it's only for "cosmetics" you might manipulate the t0 element of your waveforms to use the same start time in all of them… 🙂

[PB21]

ok, thanks very much for the advice.