NI-DAQmx Tasks Timing Settings

[ImGoodThanks]

Hello,

I’m new to LabVIEW and working on a data logging application that acquires multiple strain channels at 50 kHz, and multiple thermocouple channels at 10 Hz.

I created separate DAQmx tasks in NI MAX for each sensor type (I zero/calibrate my sensors here), and I’m using continuous sampling for both. In LabVIEW, I configure each task using DAQmx Timing VIs, where I set the sample rate (50 kHz and 10 Hz respectively).

Problem:

The thermocouple data appears to lag significantly.

1. It takes much longer to populate waveform charts and TDMS files
2. It seems delayed relative to the strain data during acquisition

Questions: 

1. Does the DAQmx Timing configuration in LabVIEW override NI MAX settings, or could there be a conflict?
2. Is using Samples = Duration × Rate for continuous sampling causing large buffer sizes and delayed reads?
3. If I need the data to be in sync for post-processing, what is the best approach for synchronization? 

Any guidance on architecture or DAQmx best practices would be greatly appreciated.

Thanks!

[Joe_H]

Please let us know what equipment you are using. Some of the daq cards for thermocouples is really slow.

[ImGoodThanks]

Yes, I have an NI 9178 8 slot chassis. 

For strain I use 5x NI 9237 DAQ's

For thermo I use 3x NI 9211 DAQ's

[ZYOng]

1. Does the DAQmx Timing configuration in LabVIEW override NI MAX settings, or could there be a conflict?

Think data flow. Whichever come later will override the previous one.

2. Is using Samples = Duration × Rate for continuous sampling causing large buffer sizes and delayed reads?

Since you are using -1 in the DAQmx Read VI, which only reads when all data has arrived, so yes.

3. If I need the data to be in sync for post-processing, what is the best approach for synchronization? 

Use channel expansion to combine multiple channels into a single task. The slower thermocouple reading will have duplicated data points on the faster strain reading.

[ImGoodThanks]

Thank you very much. 

In regard to channel expansion, as you can see I am using the data output from the DAQmx Read VI to generate channel names for my tdms file. With both task types being combined, is there a better alternative method for keeping track of channel names. 

Each pair of bi-axial strain gauges has a thermocouple associated with them, so the numbering is important.