How to Log and Export Low-Frequency Data in FlexLogger for Long-Term Measurements?

Issue Details

When working with long-term data logging applications, file size and data handling can quickly become a challenge. This is a common scenario when using a cDAQ system together with FlexLogger application.

A typical workflow is to log data at the full channel rate into TDMS files and later reduce the data frequency by exporting the data to CSV using FlexLogger’s built-in export option. While this works, the question is whether there’s another way—such as using the FlexLogger TDMS Viewer - to export or work with the data at a lower frequency.

Solution

Starting with FlexLogger 2024 Q2, a new capability was introduced that allows you to log data at a much slower rate directly during acquisition. This significantly reduces file size and removes the need for down-sampling during export.

You can configure this from the Logging Specification tab:

1. Go to Logging Specification → Logging Trigger.

2. Configure FlexLogger to log at a slower rate outside the trigger window.

3. Set up a Start Trigger that will never become true.

   • For example, create a variable and configure logging at the normal channel rate only when that variable is greater than 1.

   • If the variable is never set above 1, FlexLogger will always log at the slower, background rate.

4. Define the desired slow logging rate.

With this method, FlexLogger can log data at extremely low rates, down to 1e-5 Hz, which is approximately one data point per day.

Additional Information

The “Log data at X Hz when trigger conditions are not met” option does not average data over each interval. It simply reduces the logging rate by point sampling of the data written to the TDMS file. Once the trigger condition becomes true, logging automatically switches to the full channel rate. If averaged values are needed, this must be done later in post-processing (for example, in DIAdem).