Solution
The FlexLogger TDMS Viewer contains 3 Time Axis available configurations,
Absolute, Relative, and Relative with offset. These 3 options will not make the X-Axis of the graph adapt to the X-Axis of the calculated channel. The FlexLogger TDMs Viewer does not include the Compatible configuration included in DIAdem, this fourth Axis Configuration lets you adapt the X-Axis of a calculated Channel into a Graph. As this option is not available the FlexLogger TDMS Viewer leaves you only the other 3 modes to be selected.
There is a workaround based on creating an X channel with the X numbers of the calculated channel. Follow the next steps
1. Use the Channel function Generate Numeric Channel
2. Select Values from x-part of the waveform channel as the Channel generation mode, and drop the calculated channel you previously created (the result from the FFT calculation) in the Channel generation parameters section. Then click on Calculate
3. In the graph, use that channel created in the last step as the X-Channel, keep the Y-Channel as it was (The FFT result)