PSN-L Email List Message
Subject: Re: Seismic detector with AIS326DQ
From: ChrisAtUpw@.......
Date: Wed, 22 Apr 2009 23:39:09 EDT
In a message dated 22/04/2009, alexmirabal2000@........ writes:
I need to build a device that alarms when a seism takes place, preferably
in an early state, let's say, for being used in public buildings or schools.
It is not intended to measure and record the magnitude of the earth
movement at all, just detect once it reaches certain level in any of the 3 axis
and activate a sound/visual indication.
As a first approximation, I was taking a look to this IC: AIS326DQ
_http://www.st.com/stonline/products/literature/ds/14956/ais326dq.pdf_
(http://www.st.com/stonline/products/literature/ds/14956/ais326dq.pdf) , but honestly I
have no practical criteria to determine in advance if it sensitive enough
for my purpose. The manufacturer web page mentions it is for automotive
applications, but my feeling is that the accelerations changes in such
environments are far beyond the ones I need to deal with.
Hi Alexander,
If you look at the data sheet, the minimum detection level is 1 milli
g and you only have a 12 bit ADC. These MEMs devices do not have the high
sensitivity, low noise and resolution that I would normally consider for
seismic applications. They use 3.3V supplies and low level digital outputs,
not 5V. There is NO low pass filter to remove noise.
You still have to take measurements in the real world, with all the
environmental background noise that this entails.
See the comments about noise and drift at
_http://psn.quake.net/strongmotion.html_ (http://psn.quake.net/strongmotion.html)
Larry does offer a triaxial sensor board
_http://psn.quake.net/psnaccel/_ (http://psn.quake.net/psnaccel/)
In case you consider it not suitable for this application, could any of
you, please, recommend some other chip?
Not really. However, you can make a sensitive detector using a 44 mm
OD piezo disk from _www.digikey.com_ (http://www.digikey.com) such as
102-1170-ND @ $1.62 each with added load weights, but you do have to produce all
the electronics, filters and an ADC. This is quite a lot of work. How good
are you at designing / building electronics?
I use similar discs in flex bending mode, not as a loaded drum. You
can also buy high capacity disks already mounted in plastic cases, but their
output is nearly square law, not linear like a simple flex disk. The flex
disk that I use gives over 5x the voltage output of a 4.5 Hz L15B geophone
see _http://psn.quake.net/geophone/index.html_
(http://psn.quake.net/geophone/index.html) and the setup can go down to 10 seconds period. Note that you
may want to detect P and S waves from 0.5 Hz to 5 Hz.
Let me know if you want any further help?
I am located in Mexico City.
Regards,
Chris Chapman in UK
In a message dated 22/04/2009, alexmirabal2000@........ writes:
I need to build a device that alarms when a seism takes place, pref=
erably
in an early state, let's say, for being used in public buildings or scho=
ols.
It is not intended to measure and record the magnitude of the earth move=
ment
at all, just detect once it reaches certain level in any of the 3 axis=
and
activate a sound/visual indication.
As a first approximation, I was taking a look to this IC: AIS326DQ=
http://www.st.com/stonline/products/literature/ds/14956/ais326dq.pdf=
,
but honestly I have no practical criteria to determine in advance i=
f it
sensitive enough for my purpose. The manufacturer web page mention=
s it
is for automotive applications, but my feeling is that the accelerations=
changes in such environments are far beyond the ones I need to deal
with.
Hi Alexander,
If you look at the data sheet, the minimum
detection level is 1 milli g and you only have a 12 bit ADC. These MEMs de=
vices
do not have the high sensitivity, low noise and resolution that I would no=
rmally
consider for seismic applications. They use 3.3V supplies and low level di=
gital
outputs, not 5V. There is NO low pass filter to remove noise.
You still have to take measurements in the re=
al
world, with all the environmental background noise that this entails.=
In case you consider it not suitable for this application, could an=
y of
you, please, recommend some other chip?
Not really. However, you can make a sensitive=
detector using a 44 mm OD piezo disk from
www.digikey.com such as 102-1170-ND @=
$1.62
each with added load weights, but you do have to produce all the electroni=
cs,
filters and an ADC. This is quite a lot of work. How good are you at desig=
ning /
building electronics?
I use similar discs in flex bending mode, not=
as a
loaded drum. You can also buy high capacity disks already mounted in plast=
ic
cases, but their output is nearly square law, not linear like a simple fle=
x
disk. The flex disk that I use gives over 5x the voltage output of a 4.5=
Hz L15B
geophone see
http://psn.quake.net/geo=
phone/index.html and
the setup can go down to 10 seconds period. Note that you may want to dete=
ct P
and S waves from 0.5 Hz to 5 Hz.
Let me know if you want any further help?
I am located in Mexico City.
Regards,
Chris Chapman in UK
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