In a message dated 12/11/2009, barry_lotz@............. writes:

I found a  company called Sensr that sells 3 different data acquisition 
systems for $700  up. Not really that bad when it includes a 3 axis and  
storage.
http://www.sensr.com/products/civil-and-structural/
Regards
Barry



Hi Barry,
 
    These are commercial MEMs units with a range of 12  g to 0.05 g and 
0.001 g resolution. These are fine for making environmental  measurements on 
bridges, buildings, etc., but you need to be able to measure to  micro g 
levels for a strong motion seismometer, whether professional or amateur. 
    Larry sells a 3 axis strong motion accelerometer  board with serial 
amplifiers giving ranges of 2 g and 70 milli g maximum,  driving a 16 bit ADC. 
These give 6-9 mV / g and 1 micro V p-p noise.
    The ADXL103/203 have a range of +/-1.7 g and a  noise level of 110 
micro g / root Hz rms. For 20 Hz bandwidth the noise is about  0.7 milli g pk. 
You are relatively unlikely to observe quakes with these unless  you live 
over an area of known seismic activity.  
    Colibrys _http://www.colibrys.com/e/page/140/_ 
(http://www.colibrys.com/e/page/140/)  offer  a +/3 g range and 300 nano g rms / root Hz noise. 
However, Avnet seem to have an  unrealistic idea of the value of this sensor. I 
note that they are not stocking  them at the moment.
    I have used piezo disks from _www.digikey.com_ (http://www.digikey.com) 
 102-1170-ND at $1.62 and  668-1190-ND at $2.72 as accelerometers. Used in 
simple bending mode supported on  two sides (NOT as a circular diaphragm),  
with a central 1 oz mass on a  square brass tube support 
(_http://www.ksmetals.com/_ (http://www.ksmetals.com/) ) and a FET  input amplifier, they can 
sense right down to the seismic background noise  level. They need to be kept 
dry at all times and temperature variations need to  be reduced as far as 
possible.  I mount one with the amplifier in a glass  jam jar with a rubber 
seal metal lid and use a disk of circuit board with  feed through soldered 
pins. There is a lot more information available at 
_http://jclahr.com/science/psn/chapman/piezo/index.html_ 
(http://jclahr.com/science/psn/chapman/piezo/index.html) 
    You may feel quakes over about 0.015 g.
 
    Regards,
 
    Chris Chapman






In a message dated 12/11/2009, barry_lotz@............. writes:
I=
 found a=20
  company called Sensr that sells 3 different data acquisition systems for=
 $700=20
  up. Not really that bad when it includes a 3 axis and=20
  storage.
 http://www.sensr.com/products/civil-and-structural/Regards
Barry


Hi Barry,
 
    These are commercial MEMs units with a range=
 of 12=20
g to 0.05 g and 0.001 g resolution. These are fine for making environmenta=
l=20
measurements on bridges, buildings, etc., but you need to be able to measu=
re to=20
micro g levels for a strong motion seismometer, whether professional or am=
ateur.=20

    Larry sells a 3 axis strong motion accelerome=
ter=20
board with serial amplifiers giving ranges of 2 g and 70 milli g maxi=
mum,=20
driving a 16 bit ADC. These give 6-9 mV / g and 1 micro V p-p noise.
    The ADXL103/203 have a range of +/-1.7=
 g and a=20
noise level of 110 micro g / root Hz rms. For 20 Hz bandwidth the noise is=
 about=20
0.7 milli g pk. You are relatively unlikely to observe quakes with these=
 unless=20
you live over an area of known seismic activity.  
    Colibrys http://www.colibrys.com/e/pag=
e/140/ offer=20
a +/3 g range and 300 nano g rms / root Hz noise. However, Avnet seem to=
 have an=20
unrealistic idea of the value of this sensor. I note that they are not sto=
cking=20
them at the moment.
    I have used piezo disks from www.digikey.com 102-1170-ND at $1.62=
 and=20
668-1190-ND at $2.72 as accelerometers. Used in simple bending mode suppor=
ted on=20
two sides (NOT as a circular diaphragm),  with a central 1 oz mass on=
 a=20
square brass tube support (http://www.ksmetals.com/) and a=
 FET=20
input amplifier, they can sense right down to the seismic background noise=
=20
level. They need to be kept dry at all times and temperature variations ne=
ed to=20
be reduced as far as possible.  I mount one with the amplifier in a=
 glass=20
jam jar with a rubber seal metal lid and use a disk of circuit board=
 with=20
feed through soldered pins. There is a lot more information available at=
 http://jcl=
ahr.com/science/psn/chapman/piezo/index.html
    You may feel quakes over about 0.015 g.
 
    Regards,
 
    Chris Chapman