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Stratus Rain Gauge Design

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LABob:
I have the Stratus RG202 and I had always wondered why they didn't tweak the design a little bit so that the overflow would line up with the markings on the inner cylinder in a meaningful way. For example, if a station had received 2.1 inches of rain, wouldn't it be useful for the gauge to be designed so that the water in the overflow chamber lined up with the 0.11 mark on the inner cylinder? That would make reading total rainfall over 1-inch as easy as reading the level in the overflow chamber against the inner cylinder, multiply it by ten, and add 1 inch for the water in the inner cylinder.

LFWX:
The only way to make an accurate measurement (to the nearest 0.01") is to use the small inner tube, any markings on the large tube would just result in much less accurate measurements.

LABob:
The idea wasn't to improve accuracy, but to make it possible to read the gauge without dismantling it (like during a storm). Redesigning the gauge as I described wouldn't affect accuracy, only make it easier to use.

smorris:
Sure it would reduce accuracy. The inner cylinder is approximately a 10:1 ratio. One inch of rain fills 10 inches of cylinder. The outer cylinder is approximately 1:1 ratio, so one inch of rain (over the first one inch) fills the outer cylinder one inch. So the accuracy of the overflow would be 1/10 the accuracy of the inner cylinder.

One-hundredth of an inch of new rain in the outer cylinder would only increase the depth the thickness of 3 sheets of paper, which couldn't be distinguished.

Steve

LABob:

--- Quote from: smorris on April 05, 2013, 12:13:48 PM ---Sure it would reduce accuracy. The inner cylinder is approximately a 10:1 ratio. One inch of rain fills 10 inches of cylinder. The outer cylinder is approximately 1:1 ratio, so one inch of rain (over the first one inch) fills the outer cylinder one inch. So the accuracy of the overflow would be 1/10 the accuracy of the inner cylinder.
--- End quote ---

Why are you proposing to treat the two designs differently? You can still decant the overflow into the inner cylinder to get 1/100ths of an inch. The only change is that you would be able to read rainfall over 1 inch to the nearest 1/10th without disassembling the gauge, which is an improvement over the current design.

With an inner diameter of 4 inches, every inch of rainfall will fill a 1.155-inch ID tube with 12 inches of water. This is approximately the current design, and it works well enough. However, the entire outer cylinder is the same diameter as the funnel. Since the inner cylinder displaces some water, the depth of the water in the overflow doesn't relate in a meaningful way to the actual rainfall. If the inner diameter of the outer cylinder was changed to 4.239 inches, and the funnel kept at 4 inches, the water level in the overflow would rise one inch for every inch of rain that fell into the funnel (assuming the inner tube's walls are 1/8-inch thick).Everything would still work the same. The first inch would be readable in 1/100ths and the overflow would fill the outer cylinder. You would still decant the overflow into the inner cylinder to get 1/100ths of an inch. The only change is that while the gauge is still assembled you can glance at it and see that 2.4 inches of rain has fallen (for example). With the current design you cannot tell how much rain is in the overflow by glancing at the gauge, so I would say the accuracy has been improved in that respect without disturbing the ability to decant the overflow for higher accuracy.

EDIT: When you try to do math without double-checking your work first, you get mistakes. I corrected the calculations of diameters.

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