The weight sensor was an interesting little beast. I’ll write a long post at some point about how hard it is to figure out with a sensor how much water is in a bucket. I tried the eTape liquid sensor, various electrical sensors in the water, ultrasonic measurement of the height, and finally a weight sensor. The final one was the only one that worked at all — and it didn’t work all that well. More on that later.

However, it did sort-of work, and that can be seen here in the data between 12:45pm and about 3pm on Sunday 26 Aug. The cycling from low level to a high level shows the pump’s action. When the pump is running, most of the water is up on the evaporation tower, not in the reservoir bucket, and so the weight is low. The pump shuts off, the water drains back into the bucket, and the weight goes up.

Not *all* the water drains back. In the graph above, starting at about 13:30, imagine a straight line through the tops of the line’s plateaus. That line is tracking the loss of water due to evaporation off the tower.

There are tons of complicating factors: water is added to the system, as shown in the previous post; the measured weight is noisy because the truck (on which the whole tower sits) is jostled by wind, as people move stuff around inside, and when they climb onto the truck; and occasionally the sensor reports completely nonsensical readings. I’m working on an analysis that will control all these effects to get at evaporation rates.