Configuring the Master Timebase Source for the 9234

[MgDAQ]

I have several cDAQ modules I am using to collect data.  I am using the Write to Measurement Express vi to log the data to a tdms file. 

When reviewing the logged data files, the NI 9215's measured data provides nice timestamps to match how the DAQmx task was set up - 1000 sample rate with a 1ms Delay in the While Loop.  However, though in the same vi - different tasks, but the same while loop - the NI 9234's timestamps do not match the DAQmx task set up - 1000 sample rate with a 1ms Delay. After reading the material provided with the NI 9234, I found this maybe due to the device's own Master Timebase Source. There was documentation that stated it could be configured to be the Master Timebase Source for other modules:

Configuring the Master Timebase Source for the NI 9234 (FPGA Interface)

It is desired to have the timestamps for the measured data accross all the modules to match. We do not have the FPGA Module for LabVIEW. Is there a method in LabVIEW to have all modules use the same Master Timebase Source?  I assumed because all the data collection occures in the same while loop using the time delay of 1ms this was forced via code. This assumption appears to be incorrect from my review of the tdms data files.

The NI 9204 is providing a trigger only.

Software:

Windows 7

LabVIEW 2010 SP1

Hardware:

cDAQ-9174 Chassis

Slot 1: NI 9204

Slot 2: NI 9215

Slot 3: NI 9234

Slot 4; Empty

[Carisa_L · Accepted solution]

Hi MgDAQ,

An important concept to note is that the 9234 uses a delta-sigma converter and an oversample clock to read the analog data. There is an inherent input delay due to built-in analog and digital filtering. Since the 9215 has a lower resolution there will be a finite offset between the 9234 and 9215. I've included some documentation below:

What Are the Valid Sampling Rates for the NI 9233, NI 9234, and NI 9237?: https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z000000P6FrSAK&l=en-US

Synchronizing Dynamic Signal Acquisition (DSA) Products with NI-DAQmx:https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z000000P9uTSAS&l=en-US

Have you tried putting both modules in the same task? Alternatively you can export the 9234 sample clock and setup the tasks separately.

Best,

Carisa

[MgDAQ]

Carisa:

Putting the modules on the same task does put all modules on the same timestamp defaulting to the 9234's timebase.

Thank you for the suggestion.