mmroden
commented
2 years ago From @darraghbr : Ok, so we have a long tube with some flow going down it. Imagine if the pipe was massive, like 1 meter in diameter and far enough away from a fan so that doesn't affect your answer. You could use that wind meter to get an idea of how fast the wind is going at different points (in the diameter plane) of that duct. You will get different speed measurements at different points in that radius, it will be faster in the middle and slower towards the edges. This is because of the boundary layer effect. Now imagine you take a slice along the length of the pipe and you measure velocity from the middle of the pipe to the wall, you would get a diagram that looks like this, where the length of the arrows and the red line show you how fast flow is there. You can see at the wall of the pipe the flow is zero, that is what these wind meters fail to take into account, you are just measuring in the middle where the flow is strongest and if you try to measure very close to the wall the value you get from the wind meter won't be accurate because you are only partially loading the impeller.
Quite a bit of doubt has been cast on the accuracy of the sensirion sensor and its use as a flow meter for the papr project. The flows may be just fine for tetra, but they may be at the upper end of the dynamic range of the sensirion. @mechatroniks-git has reported that we're at 250 for certain measurements, which is the upper end of the range. We need to understand the amount of flow we have.
https://user-images.githubusercontent.com/116251/150650924-8339375e-8c06-4c54-b424-3282c6c706c7.mp4
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