Change in slope detection
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Hi
I have a bin that is filled with water, when it is full it wil start to overflow but the volume measured when it reaches the full level should be constant but due to the errors in volume sensors it is not always perfect. The level of the if the bin can be changes thus overflow could occur at a lower volume, thus i cannot use a threshold method. I also cannot use the last value of the data set to use as threshold as the volume measurement is not always perfect and could result in picking to high threshold or to low. In a perfect world the filling of bin should be straight line measurement and when overflow is reached it should be a straight line. If this was the case i could take the second derivative to find the change is slope. Unfortunately this is not the case and when i take the second order derivative I get the the results shown in the attached picture. Is there a way to detect this change in slope with better method. Keep in mind, since the level (Volume) can change and the rate at which it fills up no data set will be the same. I not not have the information of what level the bin is set in the data logs. Since the slope changes and the duration before overflow i cannot curve fit the slope as this changes between measurements. Doing it manually it is easy to spot but i need algorithm that automatically detects the change in slope. Thank for any help.
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