From: Steinar Midtskogen 
To: psnlist 
Sent: Mon, 14 Mar 2011 6:55
Subject: Re: Lehman seismometer movement


It's already at x100.  I've seen it spike off scale once before, which
as the 8.8 Chilean quake last year (13.000 km away), but this is the
irst time it's been off scale consistently for 1-2 hours (which makes
ense since this time the quake was 8200 km away).  Such quakes are
he exception, though.  I'm picking up 100+ of the aftershocks in
apan down to about 5.2, which is a more useful sensitivity (let's
ssume that we're done with the ~9 quakes for some years now...).
> The manual (which is worth reading for others using or constructing
 Lehmans) is on line at
 www.mutr.co.uk/images/seismometer.pdf
he correct link seems to be:
ttps://secure-mutr.co.uk/catalog/images/Seismometer.pdf
Hi Steinar,  =20
Both links work for me! The first is through the BGS website
and the second through the mutr catalogue.
>     I bought a x10 period extension board for my 4.5 Hz
 geophones from www.sara.pg.it It works very well and it
 effectively gives me 3 off 0.5 Hz geophones! These are
 well matched for all P and S waves.
Interesting.  How does it work?
    It uses the Robert's Circuit. You have two parallel=20
amplifiers which add, one a flat amplifier and one a 1/f=20
amplifier to compensate for the roll off of the geophone.
You use two stages in series to give a 1/f^2 response=20
tailing into the normal flat with frequency response of=20
a normal geophone. See
www.jclahr.con/science/psn/roberts/index.html or
www.jclahr.com/science/psn/epicslinks.html and click on
Roberts circuit about 1/2 way down the page.
    My one works brilliantly! You can extend the period
a bit further, but you soon run into noise problems. A =20
x30 extension would need an ADDITIONAL VLF gain of 900!
    The board wasn't very expensive.=20
    Regards,
    Chris Chapman



<=
TT>





=
From: Steinar Midtskogen <steinar@.............>

To: psnlist <psnlist@..............>

Sent: Mon, 14 Mar 2011 6:55

Subject: Re: Lehman seismometer movement





It's a=
lready at x100.  I've seen it spike off scale once before, which
was the 8.8 Chilean quake last year (13.000 km away), but this is the
first time it's been off scale consistently for 1-2 hours (which makes
sense since this time the quake was 8200 km away).  Such quakes are
the exception, though.  I'm picking up 100+ of the aftershocks in
Japan down to about 5.2, which is a more useful sensi=
tivity (let's
assume that we're done with the ~9 quakes for some years now...).

> The manual (which is worth=
 reading for others using or constructing
> Lehmans) is on line at
> www.mutr.co.uk/images/seismometer.pdf
The correct link seems to be:
https://secure-mutr.co.uk/catalog/images/Seismometer.pdf

Hi Steinar,   
Both links work for me!=
 The first is through the BGS website
and the second through the mutr catalogue.
>     I bought a x10 per=
iod extension board for my 4.5 Hz
> geophones from www.=
sara.pg.it It works very well and it
> effectively gives me 3 off 0.5 Hz geophones! These are
> well matched for all P and S waves.

Interesting.  How does it work?

    It uses the Robert's Circuit. You have two parallel 
amplifiers w=
hich add, one a flat amplifier and one a 1/f 
amplifier to compensate for the roll=
 off of the geophone.
You use two stages in series to give a 1/f^2 response <=
/TT>
tailing into the=
 normal flat with frequency response of 
a normal geophone. See
www.jclahr.con/science/psn/roberts/inde=
x.html or
www.jcla=
hr.com/science/psn/epicslinks.html and click on
Roberts circuit about 1/2 way do=
wn the page.
    My one works brilliantly! You can extend the period
a bit further, but you =
soon run into noise problems. A  
x30 extension would need an ADDITIONAL VLF gain of=
 900!
   =
 The board wasn't very expensive. 
    Regards,
    Chris Chapman