Interesting Visualization Example and Request for Analysis Strategy

If you use line and markers mode, you may be able to convince yourself that the effect is just aliasing. See my much-expanded view attached.

I wondered about de-interleaving the wave. If the three patterns are regularly spaced then you can simply pull them out by wave assignment. My second thought was that they're unlikely to be exactly interleaved so the approach wouldn't work. Having read John's comment, perhaps if they can be de-interleaved it is just an aliasing effect?

Hi,

We are going to try to higher frequency data 1000Hz vs 100Hz and  perhaps that will provide some clarity.  I will keep you posted.

There are some mechanical/physical possibilities for the overlapping signals so it could be real.  Assuming it is real but not neatly separated by point assignment any other techniques so quantifying the system?

Andy 

Take a look at this sin fit to a small portion of the data set. I think it's pretty clearly aliasing.

Hi,

We ran a higher data rate experiment 1KHz versus the original 100Hz.  The anti-aliasing is now more clear. Choosing different scales and styles highlights different aspects of the signal. The markers only with a somewhat expanded view shows the digitization of the sensor well which is expected.

The zoomed in shows a more wave-like structure though it is not a simple sine wave which is also not unexpected.

I consult on experimental strategy and data analysis and I strongly highlight the need to visualize the data.  The ability to quickly switch styles and adjust zoom while a simple feature should not be overlooked.  Most of my clients are still wallowing in an Excel so this quick analysis is often overlooked.

The higher rate data is attached for your amusement.  FYI is from Keyence laser displacement sensor and the units are mm taken over a moving substrate.

Andy

Pretty interesting. Just to drive home the point about aliasing with a sledgehammer, I have appended a graph showing all the data in red with hollow circles, and another with every tenth point in solid blue circles.

Andy- Thanks for the kind words about the easy graphing and zooming, which have been part of Igor for 30 years! The "easy" part masks a lot of pretty tricky code, especially when you zoom to extreme levels as we are doing in this thread.