In a message dated 2008/06/12, jamesridout@.............. writes:

> This is a link to a picture of my mini lehman, It is one I made from bits=20
> of scrap aluminium from work. It has a NeFe 3/4" x 1.5" magnet inside a co=
il=20
> of 6000 turns of 0.18mm enamelled copper wire, coupled directly to a chart=
=20
> recorder on the 50Mv setting NO amplification or filters ( is this wrong??=
??). I=20
> pick up constant microseisisms all the time  at about 5 secs period. The=20
> unit I have managed to tune to 15 seconds, and still be quite stable.

Hi James,

       Thanks for the photo.
       Good on the period! I run at between 20 to 30 seconds, since most of=20
the Love and Rayleigh waves come in at ~20 seconds period.
       The viscosity of oil changes by x10 every 20 C Degrees, so oil=20
damping, apart from being messy and non linear is only good after it has bee=
n set up=20
for a +/-2 C Deg operating range =3D unsatisfactory in my book! The=20
professionals dropped it in the 1940s. Then some idiot put a design on PSN i=
n the early=20
1980s and they have been coping it ever since. It is difficult to set up and=
 it=20
gives poor + variable results.
       Magnet + plate damping is dead easy now that NdFeB magnets are readil=
y=20
available and it is independant of temperature.
       The =A3315 SEP seismometer which plugs straight into a PC is shown at=
=20
http://www.bgs.ac.uk/education/school_seismology/seismometer.html
       You get the AmaSeis recording and display program free and the=20
amplifier, filters  and ADC converter are included. The computer processing=20=
allows=20
you to filter the traces and remove microseisms on screen.
       Magnetic damping was used on the first Lehman. More information is=20
available at http://jclahr.com/science/psn/chapman/index.html
       A good amplifier is shown at=20
http://jclahr.com/science/psn/cochrane/index.html
       You need to restrict the max frequency to about 5 Hz to remove the=20
large amounts of environmental noise above about 10 Hz.
        http://www.sara.pg.it/sara_en.html in Italy also sell amateur seismi=
c=20
equipment. Their list does not cover all the products that they supply. Maur=
o=20
Mariotti is very helpful.

       Let me know if you need any help or advice.

       Best Wishes,

       Chris Chapman  =20
In a me=
ssage dated 2008/06/12, jamesridout@.............. writes:



This is a link to a picture of=20=
my mini lehman, It is one I made from bits of scrap aluminium from work. It=20=
has a NeFe 3/4" x 1.5" magnet inside a coil of 6000 turns of 0.18mm enamelle=
d copper wire, coupled directly to a chart recorder on the 50Mv setti=
ng NO amplification or filters ( is this wrong????). I pick up constant micr=
oseisisms all the time  at about 5 secs period. The unit I have managed=
 to tune to 15 seconds, and still be quite stable.




Hi James,



       Thanks for the photo.

       Good on the period! I run at between 20=
 to 30 seconds, since most of the Love and Rayleigh waves come in at ~20 sec=
onds period.

       The viscosity of oil changes by x10 eve=
ry 20 C Degrees, so oil damping, apart from being messy and non linear is on=
ly good after it has been set up for a +/-2 C Deg operating range =3D unsati=
sfactory in my book! The professionals dropped it in the 1940s. Then some id=
iot put a design on PSN in the early 1980s and they have been coping it ever=
 since. It is difficult to set up and it gives poor + variable results.

       Magnet + plate damping is dead easy now=
 that NdFeB magnets are readily available and it is independant of temperatu=
re.

       The =A3315 SEP seismometer which plugs=20=
straight into a PC is shown at http://www.bgs.ac.uk/education/school_seismol=
ogy/seismometer.html

       You get the AmaSeis recording and displ=
ay program free and the amplifier, filters  and ADC converter are inclu=
ded. The computer processing allows you to filter the traces and remove micr=
oseisms on screen.

       Magnetic damping was used on the first=20=
Lehman. More information is available at http://jclahr.com/science/psn/chapm=
an/index.html

       A good amplifier is shown at http://jcl=
ahr.com/science/psn/cochrane/index.html

       You need to restrict the max frequency=20=
to about 5 Hz to remove the large amounts of environmental noise above about=
 10 Hz.

        http://www.sara.pg.it/sara_en.htm=
l in Italy also sell amateur seismic equipment. Their list does not cover al=
l the products that they supply. Mauro Mariotti is very helpful.



       Let me know if you need any help or adv=
ice.



       Best Wishes,



       Chris Chapman