Author Topic: Drop counting integrator (rain rate) experiment  (Read 3382 times)

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Offline SLOweather

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Drop counting integrator (rain rate) experiment
« on: March 15, 2012, 05:40:49 PM »
It looks like we have some rain on the way. I've done some thought-engineering, some research on R/C time constants, and some experimentation to see how I can integrate (in the calculus sense) the drop counting output of an RG11 to get a voltage signal with some sense of the rain rate.

What I have is a 1000 uf capacitor and a few resistors, 1k, 10k, and 100k, plus 2 AA cells for power. On the bench, I've experimented with charging the cap in fractions of a second increments similar to the 100 ms output of the RG11, and then discharging it through the same or different value resistor when the relay isn't closed.

The theory seems to be sound. Right now, I'm using a 10K charge resistor and 100k discharge and it works about as I would expect. Tomorrow I'll hook it up across the RG11 and see how it works, comparing voltages with the Davis console rain rate.

I'm not sure if I can figure out how to graph it, but I'll try.


Offline iisfaq

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Re: Drop counting integrator (rain rate) experiment
« Reply #1 on: March 23, 2012, 03:42:01 AM »
How did your experiment go?

Chris

Offline W3DRM

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Re: Drop counting integrator (rain rate) experiment
« Reply #2 on: March 23, 2012, 12:16:54 PM »
Chris (SLOWEATHER),

Back in the 70's when I lived in Hawaii, I spent a lot of time on the Hilo science labs at the University of Hawaii. We had computers there and one of the scientists was studying rainfall and the effects of rain-drops, in particular. He designed numerous different sensors to capture the size of a rain-drop and the rate at which they fell. One of them was a grid-like device that looked like a piece of a metal window screen except that all of the wires were insulated from each other and each one was connected to a matrix so he could detect whenever a drop of rain fell on it. That gave him a sizing based on the number wires that were activated with a drop and also the rate of rain.

The only problem he had was false readings when spiders would walk across the sensor. As far as I know, he never was able to keep the spiders off the grids.

Good luck with you experiments. Let us know how they go.

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Offline SLOweather

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Re: Drop counting integrator (rain rate) experiment
« Reply #3 on: March 24, 2012, 02:49:43 PM »
How did your experiment go?

Chris


It was OK. I just didn't have a decent way to graph the data on short notice. I did try using a Rustrak mechanical inkless chart recorder, but the non-amplified meter movement loaded down the integration circuit too much. And I forgot to read the rain rate in VWS for comparison. The idea, though, is sound. On a DMM, I could read the capacitor voltage as the relay clacked away, charging and discharging it.

I was using drop counting mode on the RG11. I think maybe a more accurate integration would be to use the sensor in 0.0001" rain gauge mode. But, to move forward, I need a better chart recorder.