LabVIEW
DAQmx 2025Q4 Pause Logging Bug
This is a bug that affects DAQmx 2025Q4 and LabVIEW 2025Q3; it also appears in LabVIEW 2021 and DAQmx 2021. I do not know what other versions it affects.
Background:
Attached is an example in LabVIEW 2019 for people to test/confirm the bug.
This example uses the built in DAQmx Logging Feature. It will write a TDMS file to your temporary folder and delete it when the VI is stopped. This VI makes use of the DAQmx Pause feature which allows one to pause saving data to the TDMS file.
This bug occurs with both real and simulated instruments. You may have to adjust the sampling rate and the number of points based on your device.
The Bug is as follows:
- The VI is started with the logging feature paused, that is, no data is saved.
- When you "un-pause" the data logging both t0 and dt are incorrect on the read function for one iteration. t0 goes to 0 and dt goes to 1. Data that is saved in the file has both the CORRECT t0 and dt, only the read function is affected.
- If you then pause the data logging both t0 and dt are correct. The bug only occurs when the pause on logging goes from the T->F transition for one iteration.
Since the logged data is correct the bug is not severe,but if in parallel you are analyzing the waveform data and depend on a valid t0 or dt, it is an issue.
Below is a screen shot of the bug. You can see the transitions in dt when the Pause button goes from T->F in the bottom plot; the bottom plot records dt for each DAQmx read iteration. (The correct dt is not 0 as it appears in the plot, it is 1/1024 which looks like 0 on the plot range.)
