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.

Results

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 :

Actual(cm)Measured(cm)%Error
8079.950.06%
6061.141.9%
4038.723.2%

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

  1. Colin Angus says:

    Some great research! Have you done any testing on the water yet?

    • wattnotions says:

      Thanks 🙂 . Haven’t done any real water tests yet. Hoping to spend some more time on this project in a few weeks.

  2. I have previously deployed buoys with the same sensor but different algorithm. Interested in trying your approach and deploying a buoy. Let me know if you want to collaborate.

    • wattnotions says:

      Hi Wayne, I would be interested in deploying this sensor on a buoy. The only thing is I’ve designed a PCB but haven’t written the firmware yet to take these algorithms and make them work on a microcontroller. I’m away travelling until the 7th November. I’ll restart the project around then and when things progress I will reach out to you . Where about are you based ? I’m in Ireland myself .

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