In a message dated 18/07/2005 19:31:08 GMT Daylight Time, mike8s2@.........
writes:
installed some larger-capacitance-value coupling capacitors on my 24-bit
sound card so I could resolve lower frequencies. What is a good datalogging app
to
use with this?
Hi Greg,
I suggest that you look at Larry's website at _http://psn.quake.net/_
(http://psn.quake.net/) and read some of the articles. Look at other websites
on _http://psn.quake.net/dave/map.htm_ (http://psn.quake.net/dave/map.htm)
A soundcard by itself has a frequency range of about 10 Hz to 24 KHz and
it is basically an AC only device. The 10 Hz lower frequency is limited by
the input C + R circuit. The standard PC drivers set the sample rate from
8,000 to 48,000 sps. Using this, you end up with simply massive files on a daily
basis and no quick way of monitoring them. I haven't seen an application
which enables you to use the soundcard ADC at really low sample rates, say 20 /
sec and return them to a file.
Assuming that you are in the States, you can buy a $25 10 bit ADC from
Dataq, but it is usual to use 12 to 16 bit ADCs. Following on a geophone, you
will need a low noise amplifier and a filter. See
_http://users.viawest.net/~aloomis/seismom.htm_ (http://users.viawest.net/~aloomis/seismom.htm) or
_http://www.jclahr.com/science/psn/amp_filt/index.html_
(http://www.jclahr.com/science/psn/amp_filt/index.html)
It is usual to limit amateur seismic sensors to frequencies of less than
10 Hz. This cuts out most of the urban traffic and environmental noise,
which is of no interest to most of us and may swamp everything else above 20 Hz.
You also need a timing system which is good to better than 1 sec.
Unfortunately, most computers are fitted with something called a 'software clock',
which can vary by minutes per day. The first seismic P waves travel at maybe
10 km / sec, so a 1 minute error would give a location error of ~380 miles.
This really is useless for seismic work and why you need a dedicated data
recording program which takes this into account.
The P and S waves are of most interest to us, since they enable you to
determine the distance of the quake from your station. Long distance P waves
are at about 1 Hz and S waves are at about 0.5 Hz, but nearby quakes have
higher frequency components.
The 'cheap' 4.5 Hz geophones can be extended down to about 0.5 Hz with a
special amplifier, but they will also pick up local and near regional quakes
on their own.
It is also possible to make a really cheap vibration detector /
seismometer using piezo disks and added weights. I use one from about 0.25 Hz to 10
Hz, but I need a FET input opamp and good screened cable to do this.
Do 'read up' about earthquakes and seismometers before you start. There
is a lot to learn!
To go beyond this very basic advice, I would need to know where you are
located, your knowledge of electronics, what tools / constructional skills
you have and how much you are prepared to spend. I am not being inquisitive,
merely practical. Commercial seismometer systems may cost several 10's of
thousands of $, but amateur systems may be made from a few $100 upwards. You can
exchange construction time + skills for ready made equipment, but the effort
may be considerable. The real art lies in not making too many mistakes.....
I hope that this hslps...
Regards,
Chris Chapman
In a message dated 18/07/2005 19:31:08 GMT Daylight Time, mike8s2@yahoo=
..com=20
writes:
<=
FONT=20
style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000=20
size=3D2>installed some larger-capacitance-value coupling capacitors on my=
=20
24-bit sound card so I could resolve lower frequencies. What is a go=
od=20
datalogging app to
use with this?
Hi Greg,
I suggest that you look at Larry's website at <=
A=20
href=3D"http://psn.quake.net/">http://psn.quake.net/ and read some=20=
of the=20
articles. Look at other websites on http://psn.quake.net/dave/map.htm=
A soundcard by itself has a frequency range of=20
about 10 Hz to 24 KHz and it is basically an AC only device. The 10=20
Hz lower frequency is limited by the input C + R circuit. The=
=20
standard PC drivers set the sample rate from 8,000 to 48,000 sps. Using=20
this, you end up with simply massive files on a daily basis and no quick way=
of=20
monitoring them. I haven't seen an application which enables you to use the=20
soundcard ADC at really low sample rates, say 20 / sec and return them to a=20
file.
Assuming that you are in the States, you can bu=
y a=20
$25 10 bit ADC from Dataq, but it is usual to use 12 to 16 bit ADCs. Followi=
ng=20
on a geophone, you will need a low noise amplifier and a filter. See http://users.viawest.=
net/~aloomis/seismom.htm or=20
http://www.jc=
lahr.com/science/psn/amp_filt/index.html
It is usual to limit amateur seismic senso=
rs=20
to frequencies of less than 10 Hz. This cuts out most of the urban traffic a=
nd=20
environmental noise, which is of no interest to most of us and may swamp=20
everything else above 20 Hz.
You also need a timing system which is good to=20
better than 1 sec. Unfortunately, most computers are fitted with something=20
called a 'software clock', which can vary by minutes per day. The first=20
seismic P waves travel at maybe 10 km / sec, so a 1 minute error would=20=
give=20
a location error of ~380 miles. This really is useless for seismic work and=20=
why=20
you need a dedicated data recording program which takes this into account.=20
The P and S waves are of most interest to us, s=
ince=20
they enable you to determine the distance of the quake from your station. Lo=
ng=20
distance P waves are at about 1 Hz and S waves are at about 0.5 Hz, but near=
by=20
quakes have higher frequency components.
The 'cheap' 4.5 Hz geophones can be extend=
ed=20
down to about 0.5 Hz with a special amplifier, but they will also pick up lo=
cal=20
and near regional quakes on their own.
It is also possible to make a really cheap=
=20
vibration detector / seismometer using piezo disks and added weights. I=
use=20
one from about 0.25 Hz to 10 Hz, but I need a FET input opamp and good=20
screened cable to do this.
Do 'read up' about earthquakes and=20
seismometers before you start. There is a lot to learn!
To go beyond this very basic advice, I would ne=
ed=20
to know where you are located, your knowledge of electronics, what tools /=20
constructional skills you have and how much you are prepared to sp=
end.=20
I am not being inquisitive, merely practical. Commercial seismometer systems=
may=20
cost several 10's of thousands of $, but amateur systems may be made from a=20=
few=20
$100 upwards. You can exchange construction time + skills for ready made=20
equipment, but the effort may be considerable. The real art lies in not maki=
ng=20
too many mistakes.....
I hope that this hslps...
Regards,
Chris Chapman