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'[EE] earthquake (I think...) vibration sensor'
2006\05\06@112939 by Mark E. Skeels

picon face
Hi, list,

Weirdly, over the last 6 months, between 12 midnight and 6 AM, when my
wife and I are sleeping, she will occasionally be awakened by a
"shaking." We live in northern Illinois, in a rural area, miles away
from any urban development, gravel pits, or anything such like. I
consistently sleep through it.

I was thinking to build a vibration sensor using a MSP430 (sorry PICers)
and one of AD's accelerometer chips, to log the disturbance.

Does anyone have any idea what kind of G range something like that
should measure?

Mark

2006\05\06@115225 by Harold Hallikainen

face picon face
I've done a little work on seismic monitoring systems for power plants,
but not enough that I can pick an acceleration off the top of my head.
USGS has great near real time data available, though. For our area, see
earthquake.usgs.gov/eqcenter/recenteqsus/Maps/US2/34.36.-122.-120_eqs.php
. You can click on a particular earthquake and see a lot of data,
including waveforms. A quick look there showed waveforms as velocities
(cm/s) instead of accelerations, but perhaps accelerations are there
somewhere.

Harold



{Quote hidden}

> -

2006\05\06@120000 by Stephen R Phillips

picon face


--- "Mark E. Skeels" <spam_OUTmeskeelsTakeThisOuTspamearthlink.net> wrote:

{Quote hidden}

http://en.wikipedia.org/wiki/Seismometer

Recomended reading :)

Stephen

Stephen R. Phillips was here
Please be advised what was said may be absolutely wrong, and hereby this disclaimer follows.  I reserve the right to be wrong and admit it in front of the entire world.

__________________________________________________
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Tired of spam?  Yahoo! Mail has the best spam protection around
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2006\05\06@125603 by David VanHorn

picon face
A short pendulum, up to 3' long, will indicate nicely, and also give you an
idea of direction to the event.

2006\05\06@143935 by davedilatush

picon face
Mark E. Skeels wrote...

>I was thinking to build a vibration sensor using a MSP430 (sorry PICers)
>and one of AD's accelerometer chips, to log the disturbance.

>Does anyone have any idea what kind of G range something like that
>should measure?

It doesn't sound like the ground movement can't be very strong,
not if you're sleeping through it.

I can't speak with any authority, but IIRC the ground
accelerations in an earthquake strong enough to cause major
building damage are in the order of a few tenths of a g or
thereabouts.

Just for reference, a sinusoidal acceleration of 1 g peak
amplitude at a frequency of 1 Hz produces a peak-to-peak
displacement of 19.56 inches.  At a given g level, displacement
varies inversely with the square of frequency.

Dave D.

2006\05\06@151001 by David VanHorn

picon face
>
>
> Just for reference, a sinusoidal acceleration of 1 g peak
> amplitude at a frequency of 1 Hz produces a peak-to-peak
> displacement of 19.56 inches.  At a given g level, displacement
> varies inversely with the square of frequency.


I'm pretty sure there have been quakes with >1G accelerations.
But you WONT sleep through them.



--
> Feel the power of the dark side!  Atmel AVR

2006\05\06@153705 by davedilatush

picon face
David VanHorn wrote...

>I'm pretty sure there have been quakes with >1G accelerations.
>But you WONT sleep through them.

Heh.  Won't survive them either, most likely.

Googling on "ground acceleration earthquake" brings up lots of
good stuff, including this link

http://www.llnl.gov/hmc/grmot.html

from Lawrence Livermore National Laboratory on earthquake ground
motion, which discusses data from the 1989 Loma Prieta quake.
Seismic stations recorded ground acceleration from about 0.05g to
0.6g depending on location and soil type.

Another good link is

http://www.geophys.washington.edu/SEIS/PNSN/EDHOME/ACCEL/accel_vs_damage.html

on ground acceleration vs. damage, with a link to a table
describing typical consequences of various acceleration levels.

At 0.007g peak ground acceleration, the effects are described as:

"Felt indoors by many, outdoors by few during the day. At night,
some awakened. Dishes, windows, doors disturbed; walls make
cracking sound. Sensation like heavy truck striking building.
Standing motor cars rocked noticeably."

>From that description, I infer that what the OP is describing is
probably well below 0.007g; he might not even be able to detect
it with one of those Analog Devices parts because of their rather
high noise level.

Dave D.

2006\05\06@154516 by David VanHorn

picon face
On 5/6/06, Dave Dilatush <.....davedilatushKILLspamspam@spam@comcast.net> wrote:
>
> David VanHorn wrote...
>
> >I'm pretty sure there have been quakes with >1G accelerations.
> >But you WONT sleep through them.
>
> Heh.  Won't survive them either, most likely.


I've read witness accounts of the water in a pool apparently lifting up,
moving over, and crashing down next to the pool, mostly in but maybe 1" or
so displaced.

--
Feel the power of the dark side!  Atmel AVR

2006\05\06@163228 by Peter

picon face
Mark E. Skeels <meskeels <at> earthlink.net> writes:

> I was thinking to build a vibration sensor using a MSP430 (sorry PICers)
> and one of AD's accelerometer chips, to log the disturbance.
>
> Does anyone have any idea what kind of G range something like that
> should measure?

It could be that 'infrasound' booming that seems to plague some people in your
country ? In that case, an infrasound microphone would be more useful.

Peter



2006\05\06@222507 by Harold Hallikainen

face picon face
The accelerometers I'm familiar with in seismic monitoring force balance
accelorometers (FBA) or solid state MEMS. The FBA has been used for a long
time and still seems to be the most sensitive (quietest). The plant I
worked with had a bunch of 3 axis FBAs. The FBA has a mass and a position
sensor and a voice coil actuator. The actuator tries to keep the mass in
the same location as the ground around it moves. Acceleration is
proportional to the current through the coil. The FBAs drive a
multichannel recorder that is constantly recording to RAM. It stops
recording so many seconds after an event so the data from prior to the
event, through the event, to its end can be recovered. One other
accelarometer that is not accurate, but provides some data is the "scratch
plate." A coated plate is put under a stylus with a mass on something like
a leaf spring. After an event, you measure the scratches and get an idea
of peak acceleration. Low tech, but better than nothing.

The plant I've been working with recently replaced all this equipment with
MEMS based accelarometers. As I recall, these are a more open loop device
that's similar to a mass on a strain gauge. The force is read and
acceleration derived. These new systems have individual recorders out at
each monitoring point providing redudancy. They can be polled by the
central controller after an event. Should communications be lost, the data
can still be recovered when communications is restored, or by going out to
the unit and recovering the data.

There's a lot of neat stuff going on in seismic monitoring. The ANSS
(something like American National Seismic System) is a really neat network
of monitors all over the country that can deliver data nearly continuously
in real time. The USGS site I posted earlier breaks the country up into
regions and reports events within a minute or two. Really neat application
of networking.

The seismic monitoring of plants and buildings is interesting. In
designing these structures, they use a mathematical model for the
structure. Once its built, the monitor "free field" ground motion plus
motion at various points on the structure. After an event, they can
compare the actual results with the predicted. It's just an ongoing
experiment.

Harold


--
FCC Rules Updated Daily at http://www.hallikainen.com

2006\05\07@044913 by Jinx

face picon face
The September 05 issue of Silicon Chip has a Build Your
Own Seismograph project

Full article is not available on-line but I can supply details
if you're interested

http://www.siliconchip.com.au/cms/A_105119/article.html

The detector is an opto-sensor on the end of a magnetically
damped horizontal pendulaum

A link in the article to the author

http://science.uniserve.edu.au/school/Seismograph/



2006\05\08@091518 by Mark E. Skeels

picon face
Thanks to all who responded. As usual, the PICList is a wonderful source
of information. Where else can you tap into a knowledge base of 2000+
engineers, technicians and scientists?

I think this is not an earthquake, but blasting of some kind nearby. So,
I'm not sure that what I need is a seismometer, exactly. It shakes the
house, so I thought to attach the device to the wall of my second story
bedroom.
The three foot mechanical pendulum might work, but I need something that
will log the disturbance. We won't be standing there when it occurs.

So I'm still thinking my best option is the accelerometers. I found some
nice pcb assys' on Sparkfun electronics site:

http://www.sparkfun.com/commerce/categories.php?cPath=23_80

I'm on vacation next week, so it will be a while before I get to this.

Thanks again,
Mark


Jinx wrote:

{Quote hidden}

2006\05\09@005941 by Richard Prosser

picon face
I saw a web page at one time where a guy had made a similar sensor by
adding weight to a loadspeaker cone. Any external vibration moved the
speaker & the cone inertia generated  a few mV of signal.
Use as large a speaker as is available.

RP

On 09/05/06, Mark E. Skeels <meskeelsspamKILLspamearthlink.net> wrote:
{Quote hidden}

> -

2006\05\10@095749 by Alan B. Pearce

face picon face
> wife and I are sleeping, she will occasionally be awakened by a
> "shaking." We live in northern Illinois, in a rural area, miles away
> from any urban development, gravel pits, or anything such like. I
> consistently sleep through it.

Sure it is not a large truck on a highway or a train? Depending on the
ground layers such a heavy transport vehicle could shake a reasonable area.

Another possibility could be subsonic vibration from a railway loco exhaust,
i.e. not actually the ground shaking. I have experienced this when a diesel
engine went past with the motor just idling - it must have been using very
little fuel at the time, and mostly pumping air through the cylinders.

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