The Arduino needs a little help to read the pulses from the tube in the form of a simple circuit. The circuit acts as a peak detector and the peaks last only about twenty microseconds.

The Arduino samples the peak detector’s output and calculates the original pulse’s amplitude. Their webpage has copious details on where to get the parts, the software and how to make it.

I've just come across a no-name non-contact, high-precision 80 GHz mmWave radar sensor for liquid level detection with a 40m ...

Switch-contact bounce is an unavoidable mechanical phenomenon and complicates the task of measuring contact resistance; this circuit uses a current source and classic analog peak-detector circuit ...