Raspberry Shake Records Rain Drops !

[John Stuart]

As described in another thread, "Building a Vault", I installed my RShake outside, in a Dry Box, to get it away from the cultural(?) noise of my house. Early this morning, I discovered the Shake's uber-sensitivity was counting drops of rain!

Here are some photos of my 'experimental' installation.  The big heavy building block is necessary to push all four corners of the box down onto the concrete, otherwise it wobbled.

 

About the time the RaspShake recored a couple of nice earthquakes, it started capturing spikes of a few thousand counts amplitude, every few minutes or so. It was lightly raining, so I suspected the rain might be the source.

Attached are two screen captures from Swarm

1. A few hours that show the frequency and amplitude of the spikes.
2. A 600,000 count spike, which was much larger that the others.

I finally figured out the light rain was collecting on the tree branches above the Vault, and occasionally a large drop of water would fall off the branch and hit the Dry Box.  But, what was the big 600,000 count spike?  Maybe a small branch fell on the box??

Here you can see where some rain water had hit and collected in the recessed top of the Dry Box.

 

But LOOK !!  A wet leaf had landed right on top of the Vault.  Could a falling leaf  hitting the massive building block, impart enough energy to bump the RaspShake by 600,000 counts??

I think not, , ,  but the soaking wet leaf did have the weight of a dozen water drops. ( 0.38 grams to be exact).

So my $15 Dry Box Vault now has a temporary roof, ready for a big storm moving in from the Pacific.

More sensitivity testing will be coming, , ,

John Stuart

Lafayette, CA

[chris...@aol.com]

Hi John 

    Could you put a plastic waste bin or another box over the top of the red box ? 
    What animals are likely to be roaming about you garden ?

    Regards, 

    Chris

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[John Stuart]

Sorry Folks, my attachments were Snagit files; so this time I have attached the correct png files..

Chris; I almost used an inverted plastic wast bin, but it wouldn't have been so photogenic.

We do have deer and wild turkeys but haven't seen any for several weeks.  

Now that I have attached usable  files, you can see the impulse spikes are very short and isolated from each other, not characteristic of an animal sniffing around. 

[chris...@aol.com]

Hi John, 

    I was not thinking of an animal sniffing around, so much as a cat, dog etc defecating close to the 

box. They often kick earth and stones over the faeces with their hind legs. The orange box would be 

something NEW - which should be inspected ! Turkeys are likely to scratch about to find food. 

    Have you tried patrolling your garden regularly at about dawn ? Rig up a remote IR camera ? That is 

what I did when I had a problem with rats. The Council Rodent Officer could not argue when presented 

with a video of the rats ! 

    Regards,

    Chris
From: John Stuart <qxst...@gmail.com>
To: RaspberryShake <raspber...@googlegroups.com>

Sent: Thu, 15 Dec 2016 6:32
Subject: [Raspberry Shake Community Forum] Re: Raspberry Shake Records Rain Drops !

Sorry Folks, my attachments were Snagit files; so this time I have attached the correct png files..

Chris; I almost used an inverted plastic waste bin, but it wouldn't have been so photogenic.

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Manual: http://manual.raspberryshake.org/
Shop: https://shop.raspberryshake.org/
Website: http://raspberryshake.org/
Do It YourSelf Page: http://raspberryshake.org/do-it-yourself
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[Mercalli]

John,
The raindrop recordings are very cool. I occasionally get the larger spike with no ringing, and I call them, "pings" because they look like sonar to me. My theory is they are caused by thermal expansion / contraction. The small ones are possibly in the acrylic case, and the larger ones could be the leveling "feet" releasing energy as they jump to a new location maybe a micron from where they were before the temperature change. This is all conjecture, but I may try putting something hard and smooth under the three support points, which should allow the feet to slide horizontally with minimal effort, without degrading the vertical response. I suppose plate glass would work, and I recall some old instruments using what they called "agate" for low friction bearings. Maybe the raindrops you recorded came with a temperature change too?

[chris...@aol.com]

Hi there,

    1 Get out a ladder / stepladder and an eyedropper or similar. 

    2 Put water in a mug. Climb the ladder and drip water on the seismometer CASE from a KNOWN 

height h. Record, extract and analyse the trace.  
    3 Get a small, light plastic pot and weigh it. Drip 50 to 100 water drops into it and weigh it again to 

find the average weight of one drop. You know the energy of one drop from 1/2 x m x V^2 = m x g x h 

    Look up the terminal velocity of raindrops for comparison.      

    Mechanical Chemical Balances used to use 60 Deg triangular "knife edge" bearings made from 

very hard Agate stone. But the triangular corners were actually lapped to form tiny cylinders which 

rolled on an optically flat counter-face. (Real sharp knife edges don't work well - the edge folds over.) 

The maximum rated load was 200 gm. The low mass EAI S102 vertical school seismometers sold by 

Engineering Acoustics Inc. also used them. These were good feedback seismometers, but they were 

expensive in comparison to an AS-1. The S102 has been out of production now for several years, but 

the IRIS.EDU website still lists them - along with the EQ1 and the VS1 - ALSO out of production ! Who 

is irresponsible for updating the IRIS website ?

    Use a long paper / cardboard tube and an electric hair drier to gently waft warm air around the 

RShake module for a minute or two. Do you see any expansion noises ? 

    You should be able to buy "Acorn" dome headed SS nuts to screw over the support points - but 

a sheet of glass is probably easier to acquire.

 

    Regards, 

    Chris

--
Some useful links:
 
Manual: http://manual.raspberryshake.org/
Shop: https://shop.raspberryshake.org/
Website: http://raspberryshake.org/
Do It YourSelf Page: http://raspberryshake.org/do-it-yourself
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[endumen]

There is a weather station as is measuring the rain in similar way:

WeatherFlow Smart Weather Stations | Indiegogo

I have not tried it though.

[Brett Nordgren]

John,

One thing that might tend to support your theory is that the majority of the spikes appear to be downward-going, which implies downward ground motion.  You might expect that raindrops would be causing downward motion, whereas other causes might be more evenly distributed betwen up and down.

Brett.