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seismograph

B

BeeJ

Jan 1, 1970
0
Looking for suggestions to create a seismograph that:
is cheap; hardware < $100
easy to build. no machining etc.
sensitive (you tell me)
rugged, can be moved easily
ties to a laptop to record
could use the mic audio input (I can write the code to graph).
accuracy not important
linear or log output
about the size of a desktop PC or smaller.
omnidirectional
 
G

George Herold

Jan 1, 1970
0
You could make a couple of LC oscillators, where the Ls were near the
pendulum, like a metal detector. Half pot cores maybe. The result
would be two audio frequencies, right into the sound card.

Won't do the Z axis as easily.

Hey, a full pot core would be super sensitive to variation in the gap
between core halves. That must be useful for something. I bet you
could resolve nanometers.

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot comhttp://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation- Hide quoted text -

- Show quoted text -

For $100 you could get a laser,some mirrors, photodiode and make an
interferometer.
(not easy though.)

George H.
Personally I think the OP needs to do more research.
 
T

Tim Williams

Jan 1, 1970
0
John Larkin said:
Hey, a full pot core would be super sensitive to variation in the gap
between core halves. That must be useful for something. I bet you
could resolve nanometers.

With mK temperature regulation, perhaps.

Say, Sloman has experience with those kinds of systems, perhaps a
collaboration is in order?

Tim
 
M

miso

Jan 1, 1970
0
You can buy geophones new from RT Clark for not much more than the
mystery surplus junk. You need to build a LNA.

If you expect to "see" long distance earthquakes, you need very low
frequency response. There are hacks to lower the resonance of the
geophone with a negative resistor. Long distance sensing is teleseismic.
Most geophones are for local shaking. That is where the negative
resistor scheme comes into play.

Check out this paper:

RT Clark is cool. If you need some data not on the website, they will
send it to you. They don't mind small orders.

Right now they are at the SEG convention in Vegas.

If you are going to use the geophone more like the manufacturers spec
sheet, they will list a termination resistance. Be sure to at least
consider the resistance of the low noise amp. These low noise op amp or
instrumentation amps are quite low impedance all by themselves.

There are plenty of designs on the internet for geophone amps, though
none are particularly impressive. I just shake my head at the designs
with jfet inputs since you will be plopping a resistor across the
geophone anyway. LTC and AD have very low noise (thermal and 1/f) amps.

I think I sound card will not work well. I'd suggest a DSA, but you want
to go cheap. If you look at ebay item 261072944165, these sound cards
come apart easily. Maybe you can mod one to go to lower frequency. They
work find on linux and windows. The converter in the one I bought is
from C-Media.
 
P

Phil Allison

Jan 1, 1970
0
"Bee Jerkoff Fuckwit "
Looking for suggestions to create a seismograph that:
is cheap; hardware < $100
easy to build. no machining etc.
sensitive (you tell me)
rugged, can be moved easily
ties to a laptop to record
could use the mic audio input (I can write the code to graph).
accuracy not important
linear or log output
about the size of a desktop PC or smaller.
omnidirectional


** What does this fucking idiot imagine he is going to detect ?

Trucks driving down the street, people walking around in the next room,
passing trains ??

FFS - do NOT feed puerile trolls like this bloody imbecile.




.... Phil
 
G

George Herold

Jan 1, 1970
0
I once clearly resolved 90 nm steps with a commercial LVDT; that's,
like, 1/10 of a wavelength of NIR light. I bet the pot core could do
better.

A parallel-plate capacitor would be interesting, too.

RV Jones made a tiltometer/ seismograph with a capacitance
micrometer.

There's a graph showing the bi-daily tilt of his lab due to the nearby
tides coming in and out.

OK a quick scan to try and find what resolution he quotes...
"Our best sensitivity gave an rms limit of 5x10^-12 mm for a recording
time constant of 1 second. and our best stability a few times 10^-9
mm per day."

Wow! that was ~1970.

George H.
 
G

George Herold

Jan 1, 1970
0
How did that work? In 1970, he could have used a mercury pool as one
electrode.

--

John Larkin                  Highland Technology Incwww..highlandtechnology.com  jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators- Hide quoted text -

- Show quoted text -

Parallel plate capacitor.

http://bayimg.com/JAFKJaaek

http://bayimg.com/jaFKkAAek

I’m not sure if those pictures will come out.

He says it took him a while (years) to report results because the
electronics was mcuh better than the mechanicals that he was making.

George H.
 
Very simple.  Attach a piece of music wire to a high point, dangle a
weight from the wire.  Have two LEDs and two photocells where the light
beam is half-blocked by the weight.  The light beams are at right angles, so
you sense N-S and E-W movement.  The photocells put out an analog
signal depending on how much light they see.  You can put fixed
magnets around aluminum vanes on the weight to damp the system.
This is basically how the pros do it.

Jon

I wonder if one of those "magic" magnetic floating globes would move
enough to
actually detect, maybe even with a webcamera

-Lasse
 
G

George Herold

Jan 1, 1970
0
Yikes, is he crushing the mica dielectrics to change the capacitance?

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot comhttp://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation- Hide quoted text -

- Show quoted text -


No, sorry it's a three paddle C measurement. The middle paddle moves
back and forth, relative to the two ends. The mica is just an
insulator between the two outer paddles. Hey, spend some of Highlands
profits and buy his book. I can almost guarantee that you'll enjoy
it. (It’s the kind of read that you have to chew through slowly
though.)

George H.
 
W

whit3rd

Jan 1, 1970
0
Looking for suggestions to create a seismograph that:

is cheap; hardware < $100
easy to build. no machining etc.

The Electronic Goldmine geophones (I bought one) are vertical
types, a spring-loaded magnet in a coil.
sensitive (you tell me)
Depends on amplifiers; generally, though wind noise (trees? Are
you inside a building?) and road noise (or nearby herd critters)
will be picked up.
rugged, can be moved easily

ties to a laptop to record

could use the mic audio input (I can write the code to graph).

Not clear if your mic input is good at the earth-movement frequencies
which are circa 1 Hz. Pro equipment uses FM modulation into analog tape
recorders (or, it did when Mt. St. Helens was acting up).
accuracy not important

linear or log output

about the size of a desktop PC or smaller.

omnidirectional

That means you need three axes of sensors; it'll cost ya. Horizontal
sensors of the geophone type aren't a surplus item, to my knowledge.

There have been multiple articles in Scientific American, in the
(late, lamented) Amateur Scientist column; check out April 1996 and
Sept 1975 and July 1979. The collected columns are available on
CD-ROM
<http://www.surplusshed.com/pages/item/m2071.html>
 
S

Spehro Pefhany

Jan 1, 1970
0
I wonder if one of those "magic" magnetic floating globes would move
enough to
actually detect, maybe even with a webcamera

-Lasse

I don't think you would want to detect movement, you would want to
measure the changes in current required to keep it stable.
 
I don't think you would want to detect movement, you would want to
measure the changes in current required to keep it stable.


apparently it has four electro magnets inside controlling the hover
I guess you could just hack into it and measure the currents

-Lasse
 
M

miso

Jan 1, 1970
0
The Electronic Goldmine geophones (I bought one) are vertical
types, a spring-loaded magnet in a coil.

Depends on amplifiers; generally, though wind noise (trees? Are
you inside a building?) and road noise (or nearby herd critters)
will be picked up.


Not clear if your mic input is good at the earth-movement frequencies
which are circa 1 Hz. Pro equipment uses FM modulation into analog tape
recorders (or, it did when Mt. St. Helens was acting up).


That means you need three axes of sensors; it'll cost ya. Horizontal
sensors of the geophone type aren't a surplus item, to my knowledge.

There have been multiple articles in Scientific American, in the
(late, lamented) Amateur Scientist column; check out April 1996 and
Sept 1975 and July 1979. The collected columns are available on
CD-ROM
<http://www.surplusshed.com/pages/item/m2071.html>

RT Clark sells a 3 component (X,Y,vertical) for $135. Like I said in my
other post, don't screw with the surplus junk. New doesn't cost that
much more, and you get specs and support.

http://www.rtclark.com

If the original poster wants to detect distant quakes, he is better off
with a 4.5Hz model than a 10Hz natural frequency. The lower frequency
geophones cost a bit more.

RT Clark sells new geophones on ebay, though I don't think they are any
cheaper than just calling them up and ordering what you want.

All these geophones have spurious frequencies. That is something to take
into account. That is why I really think buying surplus stuff like old
geophones from mil surplus is the wrong way to go. They were used in
intruder detection systems.
 
R

Robert Baer

Jan 1, 1970
0
BeeJ said:
Looking for suggestions to create a seismograph that:
is cheap; hardware < $100
easy to build. no machining etc.
sensitive (you tell me)
rugged, can be moved easily
ties to a laptop to record
could use the mic audio input (I can write the code to graph).
accuracy not important
linear or log output
about the size of a desktop PC or smaller.
omnidirectional
Use a dynamic mike..
 
S

Syd Rumpo

Jan 1, 1970
0
On 06/11/2012 16:39, John Larkin wrote:

How did that work? In 1970, he could have used a mercury pool as one
electrode.

There was an article in 'Wireless World' many years ago describing a
capacitance tiltmeter using mercury. Two containers of Hg joined with a
long flexible pipe with plates which you could adjust to sit just above
the Hg. Very sensitive.

There were also 'Mercury heave gauges' commercially available somewhat
later for use in (vertical) ground movement monitoring, but I never saw
one in real life.

As for the OP, what do you need? A geophone for local events at 10Hz or
so, or a seismometer for global events at 10mHz or so? There's a big
difference.

Cheers
 
G

gregz

Jan 1, 1970
0
Robert Baer said:
Use a dynamic mike..

Adding mass to any microphone, speaker, record player pickup,.. I like the
higher impedance of the pickups.

Greg
 
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