OpenWave #7 : Displacement measurement results – peak detect vs zero crossing

This post will detail an experiment in which the wave sensor was attached to a rotating arm at three different diameters. These diameters were 40cm, 60cm and 80cm. For each diameter, measurements were taken at two speeds to get an idea of how rotation frequency affects measurement accuracy. This gives a total of 6 sets of data.

The speeds will be referred to as speed 1 and speed 2. With speed 2 being around 1.5 to 2 times faster than speed 1.

Two seperate methods of resetting the integration counter were used and compared. The first is detecting the peaks of the acceleration signal using this to reset the integration, the second method is using the zero crossings as the reset point.


Zero crossing method:

Speed 1:

Actual(cm) Measured(cm) %Error
40 40.97 2.42%
80 81.67 2.09%
60 62.59 4.32%

Speed 2 :


Peak detect method:

Speed 1:

Actual(cm) Measured(cm) %Error
40 39.14 2.15%
80 82.24 2.8%
60 58.64 2.27%

Speed 2:

Actual(cm) Measured(cm) %Error
80 77.57 3.04%
60 60.76 1.27%
40 38.62 3.45%

The results are very encouraging. In particular it was interesting that the zero crossing method provides results very similar to the peak detect method of integration reset. Zero crossing would be the preferred method for an embedded system because it takes much less processing power to detect zero crossings compared to peaks.

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