In a message dated 2007/03/05, system98765@............. writes:

> The Dataq I have is the model DI-154RS. I bought some years ago...
> Kareem

Hi Kareem,

       That will be OK. It gives 12 bit resolution for a +/-10V input.
       You need a sensor, a seismic amplifier/filter, the ADC, a suitable 
power supply, a data recording and analysis program, a computer to record and 
analyse the signals and a time check system. The computer may need a modem to 
download programs, do time checks, send and receive sample data etc.
       The time check system may be an on-line timing signal, radio or GPS. 
This is the 'unexpected extra'. The software clocks on modern computers cannot 
be relied upon to within 30 sec per day! This is hopelessly inaccurate for 
seismic recording, when a P wave has a velocity of about 8 km/sec. A 30 sec time 
error may give over 150 miles error in the epicentre position. You need to 
know the time correct to about a second.
       It is not too difficult to make a Lehman using electromagnetic damping 
and piano wire, or ball on a plane, or crossed cylinder type suspensions. 
This should allow you to set the period to over 20 sec fairly easily - many of 
the surface waves are about this period. It is a 'good idea' to make a really 
rigid cross braced T type frame to support ALL the components INCLUDING the 
damper and the sensor magnets. Make the arm and mass out of non magnetic materials 
and put the sense and damper magnets on the base frame. You set up the arm, 
sensor and damper alignment first and then set the cross balance and period 
using three levelling screws on the frame.   
       See http://www.jclahr.com/science/psn/chapman/school/MKII/index.html 
for a general layout. This seismometer was made in a machine shop. It uses a SS 
ball on a carbide plane and a wire suspension. The brass mass is at the end 
of the arm, then comes the quad sense magnet and the white pickup coil, then 
the suspension block and then the damping plate + the quad sliding magnet. The 
sense arm is about 2 ft long, the base about 2 ft 6 in and the frame height 
about 1 ft 6 in. I use 3" x 1" x 1/8" thick U Channel Al, large 8" triangular x 
3/16" thick bolt on Al corner plates and 1/4" SS bolts. 
       {Point and knife edge suspensions may severely limit the period and 
are not likely to be satisfactory long term. Oil damping is strongly temperature 
dependant and messy. Oil 'creeps' slowly over most surfaces and then attracts 
dust. Systems which use separate mounting/damping/sensing components may be 
much more difficult to set up and to adjust. You really don't need these sort 
of problems.}
       You will also need a thermally insulating, completely draft proof 
'inverted box' type cover. See http://pages.prodigy.net/fxc/seiscoverslg.jpg  It 
is quite large! I use 2" Celotex with the joints taped and glued with 
polyurethane foam grouting, both from building supplies. You can make two layer viewing 
windows out of clear mylar transparency copying film or cellophane sheet. If 
you don't make a screening box, you will get a lot of 'noise' due to air 
turbulence moving the arm. You will probably need a small heater, maybe 10 to 20 
Watts inside the top of this housing to prevent air convection noise in the late 
evening / early morning.
       It is up to you whether you buy or can make the amplifier/filter. You 
can buy +/-12V stabilised power supplies fairly cheaply. If you buy Larry's 
amplifiers, he will supply an inexpensive wall plug transformer to drive them - 
the supply regulators are built into his boards.

       NOTE: A large seismometer setup can damage your wealth!
       Check your wallet out first? Hope that this helps!

       Chris Chapman   
In a me=
ssage dated 2007/03/05, system98765@............. writes:



The Dataq I have is the model=20=
DI-154RS. I bought some years ago...

Kareem




Hi Kareem,



       That will be OK. It gives 12 bit resolu=
tion for a +/-10V input.

       You need a sensor, a seismic amplifier/=
filter, the ADC, a suitable power supply, a data recording and analysis prog=
ram, a computer to record and analyse the signals and a time check system. T=
he computer may need a modem to download programs, do time checks, send and=20=
receive sample data etc.

       The time check system may be an on-line=
 timing signal, radio or GPS. This is the 'unexpected extra'. The sof=
tware clocks on modern computers cannot be relied upon to within 30 sec per=20=
day! This is hopelessly inaccurate for seismic recording, when a P wave has=20=
a velocity of about 8 km/sec. A 30 sec time error may give over 150 miles er=
ror in the epicentre position. You need to know the time correct to about a=20=
second.

       It is not too difficult to make a Lehma=
n using electromagnetic damping and piano wire, or ball on a plane, or cross=
ed cylinder type suspensions. This should allow you to set the period to ove=
r 20 sec fairly easily - many of the surface waves are about this period. It=
 is a 'good idea' to make a really rigid cross braced T type frame to suppor=
t ALL the components INCLUDING the damper and the sensor magnets. Make the a=
rm and mass out of non magnetic materials and put the sense and damper magne=
ts on the base frame. You set up the arm, sensor and damper alignment first=20=
and then set the cross balance and period using three levelling screws on th=
e frame.   

       See http://www.jclahr.com/science/psn/c=
hapman/school/MKII/index.html for a general layout. This seismometer was mad=
e in a machine shop. It uses a SS ball on a carbide plane and a wire suspens=
ion. The brass mass is at the end of the arm, then comes the quad sense magn=
et and the white pickup coil, then the suspension block and then the damping=
 plate + the quad sliding magnet. The sense arm is about 2 ft long, the base=
 about 2 ft 6 in and the frame height about 1 ft 6 in. I use 3" x 1" x 1/8"=20=
thick U Channel Al, large 8" triangular x 3/16" thick bolt on Al corner plat=
es and 1/4" SS bolts. 

       {Point and knife edge suspensions may s=
everely limit the period and are not likely to be satisfactory long term. Oi=
l damping is strongly temperature dependant and messy. Oil 'creeps' slowly o=
ver most surfaces and then attracts dust. Systems which use separate mountin=
g/damping/sensing components may be much more difficult to set up and to adj=
ust. You really don't need these sort of problems.}

       You will also need a thermally insulati=
ng, completely draft proof 'inverted box' type cover. See http://pages.prodi=
gy.net/fxc/seiscoverslg.jpg  It is quite large! I use 2" Celotex with t=
he joints taped and glued with polyurethane foam grouting, both from buildin=
g supplies. You can make two layer viewing windows out of clear mylar transp=
arency copying film or cellophane sheet. If you don't make a screening box,=20=
you will get a lot of 'noise' due to air turbulence moving the arm. You will=
 probably need a small heater, maybe 10 to 20 Watts inside the top of this h=
ousing to prevent air convection noise in the late evening / early morning.<=
BR>
       It is up to you whether you buy or can=20=
make the amplifier/filter. You can buy +/-12V stabilised power supplies fair=
ly cheaply. If you buy Larry's amplifiers, he will supply an inexpensive wal=
l plug transformer to drive them - the supply regulators are built into his=20=
boards.



       NOTE: A large seismometer setup can dam=
age your wealth!

       Check your wallet out first? Hope that=20=
this helps!



       Chris Chapman  =20