Chris, sorry for all the typos as I hit a button and off the response =
went.
So if you would, please just read between the gaps and over the wrong =
words
as I did not edit it in any way=85  To try and answer the remainder of =
your
questions: As for a selection of seismometers, The Lehman design was =
best
because as it only took simple tools to build one. As you may already =
know
the Professor that designed it and published the original Scientific =
America
plans is also a member of this group. In the photo of your system below =
you
provided, which I have looked at and admired many times before, it =
provides
a good example of what you can build once you have mastered the original
Lehman design.  As for the amp design, as I said below, Pete Rowe =
provided a
detailed two page design for building amps/filters and gave the design
freely to the group. There has never been a lot of planning for any one
aspect of the sensors people use, just a lot of experimentation. For
example, I once built a Lehman for $5 from a toilet tank float filled =
with
water and a brass rod. Ed Cranswick told me to keep the cover down on =
the
enclosure if anybody dropped by to see my insulation=85 There was a =
member the
contributed in the early days. One by the name of Sam Gazdic in Oakland, =
CA
who provided a lot of information about sensors and systems. He worked =
for
the State of California and became a valuable resource when you had a
question about commercial seismographs. Bob Ogburn was in the National =
Guard
and worked in electronics in the Valley. He developed an array of =
sensors
using 4-inches of PVC pipe filled with oil for damping and =BD of a =
flutter
fan from the old Apple cooling systems fans. Then there were also the =
real
old-timers Howard and Woody; the first =93public citizens=94 to install =
and run
seismic sensors in their homes. Howard and Woody never formally joined =
the
PSN meetings but they did help with pen motors, chart recorders and =
sensors.
They lived in the North Bay and in the 40=92s were running seismographs =
and
chart recorders. (I think the Sprengnether Jan Froom is letting me use
actually belonged to Woody before he passed? Anyway-- ). Howard told us =
over
lunch one day that Offenhauser at the Berkeley Seismology Lab would call
them in the 40=92s after WWII to see if they recorded an event and to =
argue
over the magnitude. Woody had the best seismic shed/workroom that I have
ever seen. He had his cart reorders, HAM radio equipment and workbenches =
all
neatly laid out with seismic traces and travel time charts on the walls. =
It
was the kind of place you could just hangout in for days at a time.=20

=20

I think the thing about the PSN I like the best is that is continues to
provide a framework where people to can share information and ideas. =
There
are really only two rules in the PSN that we all agreed upon. (1) =
Don=92t have
any rules. (2)Never have a meeting more than once a year. When BBS=92s =
were
being replaced with Internet websites Larry said he wanted to develop a =
web
presence which he did. Larry=92s contributions has enabled people all =
over the
world to join in on what started as a local Bay Area thing. As you =
already
know the PSN is a worldwide organization and I feel that it sets a good
example by showing what can be accomplished when people come together =
with
respect and an openness to communicate and share.=20

=20

Thanks for your note, I hope I answered your questions. Regards, Steve
Hammond PSN San Jose, Aptos CA

=20

From: psnlist-request@.............. =
[mailto:psnlist-request@...............
On Behalf Of Stephen Hammond
Sent: Friday, April 27, 2012 1:17 PM
To: chrisatupw@.......
Cc: psnlist@..............
Subject: RE: Peoples Seismograph Array ---> Public Seismic Network

=20

Hi Chris, Thanks for your note and all the references. As for the =
Lehman=92s I
currently have, I=92m very unhappy with them and they are headed for =
scrap.
When I was in San Jose I had 40CM booms and they worked very well and =
had
25-30 second periods. I had to cut the booms down due to space issues on =
my
small property here in Aptos, after moving  from San Jose and the =
periods
went from  30 second to 10. I also live uphill from Monterey Bay and the
waves to my west and the main street to the east create lots of noise. =
So I
have to deal with that a lot of times and when the storms come in the
Lehman=92s are unusable.  Jan Froom just lent me a  Sprengnether  which =
is
running after being rebuilt at this point and I=92m still testing the =
lower
pivot I built for it. If you look at AT2 on-line over the last week or =
two
you will see the Sprengnether at a gain of 210.  I=92m still waiting for =
the
first local event. The period is not too long at this point. I think I =
need
to pull it apart again and tweak the position of the pivot  as one of =
the
two cylinder magnets is too close to the coil. When the Springnether =
gets
going I=92m pulling the two Lehman=92s. The cup / point lower pivot has =
never
worked that well. I already have three HS10=92s which were originally in =
the
old Cal-Net run by the USGS. They work really well. As for the amp and
filter designs, they came from Pete Rowe in 1990 and are on the San Jose =
PSN
site. Ted Black wrote the original PSN code and we built or own A/D =
boards
and wrote our own hardware interface drivers in Assembler. Later, after
Larry joined, he developed his hardware data collection  and software =
and I
continue to us it today.=20

=20

About the history:  As Ed Cranswick told the story over beers several =
times
he needed a grant to go to the AGU meeting that year and he published =
the
=93Peoples=94 Seismic Array paper ( which is listed in the link you =
provided) so
he could attend the meeting and present his paper. He and Phil (a =
software
engineer) had been working together on a number of projects and  If I
remember correctly it did have something to do with his work in Turkey =
or
Russia but I=92ve lost that point and can=92t recall it. Anyway, Ed got =
his
funding and went to the AGU meeting with Phil and Ed presented their =
work.
Like I SAID, IT HAD ABSOLUTLY NOTHING TO DO WITH US. Than in Oct. 1989 =
the
Loma P event went off in Aptos (Santa Cruz County) and it sparked a lot =
of
interest in seismology. However, before Oct/89 inside IBM there was a =
group
of people that had been working on their hobby, not a formal IBM =
product,
which was seismology instrumentation. Jan From, Ted Blank, Dick and one
outsider, Pete Row had already hooked-up and were sharing information. =
Jan
was a tools programmer for IBM and wrote the software to float a 3,000 =
pound
block of granite on streams of air so that master servo tracks could be
written error free on large DASD packs and lived in Gilroy, CA. Ted =
Blank
was IBM=92s performance export for the MVS operating system and lived in =
New
York and worked at the Poughkeepsie, NY plant. Pete Row was a contractor =
and
worked on secret electronics government projects here in San Jose, CA. =
Ted
had written his SDAS software for data collection on a PC and had built =
from
the 1956 plans a Lehmann seismograph. Jan had communicated via IBM=92s
internal discussion network and gotten the software and info from Ted =
and
shared it with Pete as they were HAMs on the local 2m radio network and =
both
had built and operated seismic stations. They would share info and data =
via
the local 2m network here in San Jose run by Bruce Kenny (W6TED). I (and =
250
other people) was working on developing IBM=92s OSI software product at =
the
IBM Scientific Center in Palo Alto and lived I lived in south San Jose. =
Jan
shared his plans and Ted=92s software with me and I built a Lehman and =
hooked
it to a PC via an A/D board and amp I built from sample chips I got from
local vendors. Dick Chelberg was an engineer working in the IBM plant
developing DASD in  San Jose and as a side profession operated a =
complete
machine shop at his home. He had machined a Lehman and was also using =
Ted=92s
software and an IBM A/D card to collect seismic data. One Saturday =
morning
following we got together for coffee and donuts at my home to meet face =
to
face and talk about seismographs and share info. As we were all using =
Ted=92s
software we needed a way to share the datasets so I volunteered to =
install a
BBS. Within a few weeks it was operational and the IBM Think Magazine =
folks
got wind of this seismic group operating in San Jose and asked to write =
an
employee focus item for the Company Think Magazine and they interviewed =
each
of us and wrote the article. The interesting thing was tha6t totally
unrelated, Ed=92s AGU paper was discussed in the San Jose Mercury News. =
And on
that Saturday morning we had kicked around a few names for the BBS and =
it
ended up being named =93THE =93PUBLIC=94 SEISMIC NETWORK=94 in San Jose. =
So when we
read about ED I called him at the USGS in Menlo Park and  the next day =
he
showed up at my house to see what we were doing. From that point on our
relationship grew with lots of support from the USGS and lots of great
advice. John Lahr, Ed and two other=92s stared to attend our meetings =
and as
the word about the PSN got around more and more people in the Bay Area
started to join the group. So did the BBS network. Jerry and Dorothy =
Darby
were part of the 2M radio group in Pasadena and they installed a PSN BBS =
and
were linked them together with nightly mail runs and file sharing. They =
also
were operating seismographs at their home as were a number of folks in =
the
LA area. Charlie Daniels In Memphis, TN had a seismograph and installed =
the
PSN BBS in Tennessee and link it into our network. The folks at CERI =
also
supported his site and gave him access to info on New Madrid. Allen Lynn =
was
the Station Chief at the USGS in Menlo Park and asked me to install a =
PSN
BBS in his office. Latterly, on top of a filing cabinet in his office, =
which
I did.  I maintained it via FTP  and later John Lahr took over its
operation. So the original PSN network was a four-node BBS network and =
the
members could post mail and event files to any of the systems and in =
turn a
number of elementary schools and high schools started using the systems =
in
their course work. I helped to install systems and seismographs at MT =
View
and Los Altos high schools and Anderson Elementary in San Jose. Jan
installed systems at the Gilroy Middle school and today created and
maintains the seismic system and Gilroy Gardens. Pete and Ted are still
active here on the list and the last time I check, Bruce and Dick lived =
here
in CA. Ed Cranswick was in Australia and we are still arguing over who =
was
first, the Peoples or Public Seismic Network. I=92ll have to check the
publication dates to see.=20

Regards, Steve Hammond PSN San Jose, Aptos, CA

=20

From: chrisatupw@....... [mailto:chrisatupw@...........
Sent: Thursday, April 26, 2012 5:59 PM
To: shammon1@.............
Subject: Peoples Seismograph Array ---> Public Seismic Network

=20

Dear Steve Hammond,

=20

**** Edward Cranswick wrote:

http://dominicapsn.freeyellow.com/PSN/PSN_History.html back in 1996=20

regarding the PSA / PSN history. But the attached EOS supplement is =
dated
1990.=20

    It looks like the Peoples Seismic Array project was first considered =
in
1985 ?=20

    Larry Cochrane's first PSN Internet file was in the 4th quarter of =
1995=20

=20
     I have spoken to Larry and he suggested contacting you regarding =
the=20
historical development stages of PSA / PSN before 1996. What were the =
plans
for=20
the seismometers, please ? Or were you planning to use extended period
geophones ?=20
How did the proposals develop please ? =20
=20
    I visited your web site and noted that both Lehmans were set at 12=20
seconds period. This is much less than the 25 to 30 seconds that we use=20
to match the Love waves and I wondered why you had chosen it, please ?=20
The boom length of 30 cm is much shorter than we usually use.=20
=20
Our Seismometer developments =20
   Point in a cup and knife edge "bearings" are both fundamentally =
flawed=20
designs. I suspect that the idea of using "knife edge" bearings may have =

originated from chemical balances - but their bearings are ONLY CALLED =
that
!=20
The Agate bar is cut and polished with 60 degree corners, but the =
bearing=20
corner was then carefully lapped to a tiny cylinder to take the rated =
load=20
--- of just 200 gm !! A razor sharp Agate edge would shatter easily.=20
=20
    Two bearing types which WILL take typical seismometer loads of =
several
kg=20
are a plane rolling on a ball - in my case a section of a SS scalpel =
blade
on=20
a SS ball bearing - and crossed cylinders. These can be hardened EN57 =
steel
rod,=20
or more usually tungsten carbide rods. Tungsten carbide needle roller
bearings are=20
produced. You can buy 1/8" OD tungsten carbide drills and use the shank
ends, but=20
there are plenty of small WC milling cutters with parallel shanks. I got =
a
free=20
supply of broken cutter shanks from a small engineering business just by
asking !=20
=20
    I described the test results of these and of rolling foil and wire =
very
low=20
dynamic loss, high load flexures in a paper in ArchivX. The traditional
crossed=20
foil and wire type suspensions show energy loss and noise due to the =
flexure

being bent very close to the clamped ends.=20
 =20
    Below is a photo of the seismometer that I use
 
http://www.jclahr.com/science/psn/chapman/2008%20lehman/index.html=20
    I can set the period to 30 seconds quite easily to sense the Love=20
waves at their full amplitude. The principle features are a SS scalpel=20
blade rolling on a 1/2" SS ball bearing lower fulcrum. The V cable top=20
support prevents the arm from rotating about it's long axis - this can=20
produce an undamped peak at 3~8 Hz in the FFT display if it is not=20
suppressed. The quad Neodymium magnet damping and sensor blocks are=20
highly effective. A 1/16" thick horizontal Copper damping blade is used. =

Soft Aluminum can also be used, but it is significantly diamagnetic and=20
has double the resistivity. It is also relatively difficult to buy. One=20
advantage of this design is that the magnet block can be slid along the=20
base bar to cover just as much of the N/S magnet joint as is required.=20
This butted N/S magnet joint develops a much greater damping force than=20
a widely spaced poles. The damping force required depends on the period=20
of the arm as well as on the seismic mass. The sensor block uses 1.5"=20
long magnets and a rectangular coil. This allows the arm to drift +/-=20
1/2" without any change in the sensitivity. A relatively few number of=20
turns is required on the coil - 1,500 to 2,000. The sensitivity is about =

20x that of a traditional Alnico U magnet + relay coil.=20
=20
    A Manual for the commercial SEP UK school seismometer is at=20
     
http://www.mindsetsonline.co.uk/images/Seismometer.pdf=20
    The amplifier band pass is from 0.016 to 5 Hz and the gain can be=20
switched x100, x200 or x500. The UK is a crowded noisy island with very=20
few local quakes, so a 5 Hz LP filter is optimal. The period is set by=20
tilting the base plate and a value of 25 to 30 seconds is usually =
chosen.=20
The suspension is 1/8" OD crossed tungsten carbide needle rollers. The=20
mass is brass. The boom is ~56 cm long. The extended period traces =
enable=20
you to pick up at least twice the number of quakes identified by a P&S=20
wave trigger. You pick out the often large surface waves and then look=20
for the P&S waves. =20
    This is a very successful project. Over 400 seismometers have been=20
sold since Easter 2007.=20
=20
    Regards,=20
=20
    Chris Chapman MA Oxon (Physics-retired)













Chris, sorry for all the typos as I hit a button and off =
the
response went. So if you would, please just read between the gaps and =
over the
wrong words as I did not edit it in any way… =A0To try and answer =
the
remainder of your questions: As for a selection of seismometers, The =
Lehman
design was best because as it only took simple tools to build one. As =
you may already
know the Professor that designed it and published the original =
Scientific
America plans is also a member of this group. In the photo of your =
system below
you provided, which I have looked at and admired many times before, it =
provides
a good example of what you can build once you have mastered the original =
Lehman
design. =A0As for the amp design, as I said below, Pete Rowe provided a =
detailed
two page design for building amps/filters and gave the design =A0freely =
to the
group. There has never been a lot of planning for any one aspect of the =
sensors
people use, just a lot of experimentation. For example, I once built a =
Lehman
for $5 from a toilet tank float filled with water and a brass rod. Ed =
Cranswick
told me to keep the cover down on the enclosure if anybody =
dropped
by to see my insulation… There was a member the contributed in the =
early
days. One by the name of Sam Gazdic in Oakland, CA who provided a lot of
information about sensors and systems. He worked for the State of =
California and
became a valuable resource when you had a question about commercial
seismographs. Bob Ogburn was in the National Guard and worked in =
electronics in
the Valley. He developed an array of sensors using 4-inches of PVC pipe =
filled
with oil for damping and =BD of a flutter fan from the old Apple cooling =
systems
fans. Then there were also the real old-timers Howard and Woody; the =
first “public
citizens” to install and run seismic sensors in their homes. =
Howard and
Woody never formally joined the PSN meetings but they did help with pen =
motors,
chart recorders and sensors. They lived in the North Bay and in the =
40’s
were running seismographs and chart recorders. (I think the Sprengnether
Jan Froom is letting me use actually belonged to Woody before he passed?
Anyway-- ). Howard told us over lunch one day that Offenhauser at the =
Berkeley Seismology
Lab would call them in the 40’s after WWII to see if they recorded =
an event
and to argue over the magnitude. Woody had the best seismic =
shed/workroom that
I have ever seen. He had his cart reorders, HAM radio equipment and =
workbenches
all neatly laid out with seismic traces and travel time charts on the =
walls. It
was the kind of place you could just hangout in for days at a time. =


 

I think the thing about the PSN I like the best is that =
is
continues to provide a framework where people to can share information =
and
ideas. There are really only two rules in the PSN that we all agreed =
upon. (1)
Don’t have any rules. (2)Never have a meeting more than once a =
year. When
BBS’s were being replaced with Internet websites Larry said he =
wanted to
develop a web presence which he did. Larry’s contributions has =
enabled people
all over the world to join in on what started as a local Bay Area thing. =
As you
already know the PSN is a worldwide organization and I feel that it sets =
a good
example by showing what can be accomplished when people come together =
with
respect and an openness to communicate and share. 

 

Thanks for your note, I hope I answered your questions. =
Regards,
Steve Hammond PSN San Jose, Aptos CA

 





From:=

psnlist-request@.............. [mailto:psnlist-request@............... =
On
Behalf Of Stephen Hammond

Sent: Friday, April 27, 2012 1:17 PM

To: chrisatupw@.......

Cc: psnlist@..............

Subject: RE: Peoples Seismograph Array ---> Public Seismic =
Network





 

Hi Chris, Thanks for your note and all the references. As =
for
the Lehman’s I currently have, I’m very unhappy with them =
and they
are headed for scrap. When I was in San Jose I had 40CM booms and they =
worked
very well and had 25-30 second periods. I had to cut the booms down due =
to
space issues on my small property here in Aptos, after moving  from =
San
Jose and the periods went from  30 second to 10. I also live uphill =
from
Monterey Bay and the waves to my west and the main street to the east =
create
lots of noise. So I have to deal with that a lot of times and when the =
storms
come in the Lehman’s are unusable.  Jan Froom just lent me a
 Sprengnether  which is running after being rebuilt at this =
point and
I’m still testing the lower pivot I built for it. If you look at =
AT2
on-line over the last week or two you will see the Sprengnether at a =
gain of
210.  I’m still waiting for the first local event. The period =
is not
too long at this point. I think I need to pull it apart again and tweak =
the
position of the pivot  as one of the two cylinder magnets is too =
close to
the coil. When the Springnether gets going I’m pulling the two
Lehman’s. The cup / point lower pivot has never worked that well. =
I
already have three HS10’s which were originally in the old Cal-Net =
run by
the USGS. They work really well. As for the amp and filter designs, they =
came
from Pete Rowe in 1990 and are on the San Jose PSN site. Ted Black wrote =
the
original PSN code and we built or own A/D boards and wrote our own =
hardware
interface drivers in Assembler. Later, after Larry joined, he developed =
his
hardware data collection  and software and I continue to us it =
today. 

 

About the history:  As Ed Cranswick told the story =
over
beers several times he needed a grant to go to the AGU meeting that year =
and he
published the “Peoples” Seismic Array paper ( which is =
listed in
the link you provided) so he could attend the meeting and present his =
paper. He
and Phil (a software engineer) had been working together on a number of
projects and  If I remember correctly it did have something to do =
with his
work in Turkey or Russia but I’ve lost that point and can’t =
recall
it. Anyway, Ed got his funding and went to the AGU meeting with Phil and =
Ed
presented their work. Like I SAID, IT HAD ABSOLUTLY NOTHING TO DO WITH =
US. Than
in Oct. 1989 the Loma P event went off in Aptos (Santa Cruz County) and =
it
sparked a lot of interest in seismology. However, before Oct/89 inside =
IBM there
was a group of people that had been working on their hobby, not a formal =
IBM
product,  which was seismology instrumentation. Jan From, Ted =
Blank, Dick
and one outsider, Pete Row had already hooked-up and were sharing =
information.
Jan was a tools programmer for IBM and wrote the software to float a =
3,000
pound block of granite on streams of air so that master servo tracks =
could be
written error free on large DASD packs and lived in Gilroy, CA. Ted =
Blank was
IBM’s performance export for the MVS operating system and lived in =
New
York and worked at the Poughkeepsie, NY plant. Pete Row was a contractor =
and
worked on secret electronics government projects here in San Jose, CA. =
Ted had
written his SDAS software for data collection on a PC and had built from =
the 1956
plans a Lehmann seismograph. Jan had communicated via IBM’s =
internal
discussion network and gotten the software and info from Ted and shared =
it with
Pete as they were HAMs on the local 2m radio network and both had built =
and
operated seismic stations. They would share info and data via the local =
2m
network here in San Jose run by Bruce Kenny (W6TED). I (and 250 other =
people)
was working on developing IBM’s OSI software product at the IBM
Scientific Center in Palo Alto and lived I lived in south San Jose. Jan =
shared
his plans and Ted’s software with me and I built a Lehman and =
hooked it
to a PC via an A/D board and amp I built from sample chips I got from =
local
vendors. Dick Chelberg was an engineer working in the IBM plant =
developing DASD
in  San Jose and as a side profession operated a complete machine =
shop at
his home. He had machined a Lehman and was also using Ted’s =
software and
an IBM A/D card to collect seismic data. One Saturday morning following =
we got
together for coffee and donuts at my home to meet face to face and talk =
about
seismographs and share info. As we were all using Ted’s software =
we
needed a way to share the datasets so I volunteered to install a BBS. =
Within a
few weeks it was operational and the IBM Think Magazine folks got wind =
of this
seismic group operating in San Jose and asked to write an employee focus =
item
for the Company Think Magazine and they interviewed each of us and wrote =
the
article. The interesting thing was tha6t totally unrelated, Ed’s =
AGU
paper was discussed in the San Jose Mercury News. And on that Saturday =
morning
we had kicked around a few names for the BBS and it ended up being named
“THE “PUBLIC” SEISMIC NETWORK” in San Jose. So =
when we
read about ED I called him at the USGS in Menlo Park and  the next =
day he
showed up at my house to see what we were doing. From that point on our
relationship grew with lots of support from the USGS and lots of great =
advice.
John Lahr, Ed and two other’s stared to attend our meetings and as =
the
word about the PSN got around more and more people in the Bay Area =
started to
join the group. So did the BBS network. Jerry and Dorothy Darby were =
part of
the 2M radio group in Pasadena and they installed a PSN BBS and were =
linked
them together with nightly mail runs and file sharing. They also were =
operating
seismographs at their home as were a number of folks in the LA area. =
Charlie
Daniels In Memphis, TN had a seismograph and installed the PSN BBS in =
Tennessee
and link it into our network. The folks at CERI also supported his site =
and gave
him access to info on New Madrid. Allen Lynn was the Station Chief at =
the USGS
in Menlo Park and asked me to install a PSN BBS in his office. Latterly, =
on top
of a filing cabinet in his office, which I did.  I maintained it =
via FTP
 and later John Lahr took over its operation. So the original PSN =
network
was a four-node BBS network and the members could post mail and event =
files to
any of the systems and in turn a number of elementary schools and high =
schools
started using the systems in their course work. I helped to install =
systems and
seismographs at MT View and Los Altos high schools and Anderson =
Elementary in
San Jose. Jan installed systems at the Gilroy Middle school and today =
created
and maintains the seismic system and Gilroy Gardens. Pete and Ted are =
still
active here on the list and the last time I check, Bruce and Dick lived =
here in
CA. Ed Cranswick was in Australia and we are still arguing over who was =
first,
the Peoples or Public Seismic Network. I’ll have to check the =
publication
dates to see. 

Regards, Steve Hammond PSN San Jose, Aptos, =
CA

 



From:=
 =
chrisatupw@.......
[mailto:chrisatupw@........ 

Sent: Thursday, April 26, 2012 5:59 PM

To: shammon1@.............

Subject: Peoples Seismograph Array ---> Public Seismic =
Network



 































Dear
Steve Hammond,





 <=
o:p>





****
Edward Cranswick wrote: http://dominicapsn.freeyellow.com/PSN/PSN_Hist=
ory.html back in 1996 =
<=
o:p>





regarding
the PSA / PSN history. But the attached EOS supplement is dated =
1990. <=
o:p>





   =

It looks like the Peoples Seismic Array project was first considered in =
1985 ? <=
o:p>





   =

Larry Cochrane's first PSN Internet file was in the 4th quarter of =
1995 



 
     I have =
spoken to Larry and he suggested contacting you regarding the =
historical development stages of =
PSA / PSN before 1996. What were the plans for 
the seismometers, please ? Or =
were you planning to use extended period geophones ? 
How did the proposals develop =
please ?  
 
    I visited your web site and noted that =
both Lehmans were set at 12 
seconds period. This is much less =
than the 25 to 30 seconds that we use 
to match the Love waves and I =
wondered why you had chosen it, please ? 
The boom length of 30 cm is much =
shorter than we usually use. 
 
=
Our Seismometer developments =
 
=
   Point in a cup and =
knife edge "bearings" are both fundamentally flawed =
designs. I suspect that the idea =
of using "knife edge" bearings may have 
originated from chemical balances =
- but their bearings are ONLY CALLED that ! 
The Agate bar is cut and polished =
with 60 degree corners, but the bearing 
corner was then carefully lapped =
to a tiny cylinder to take the rated load 
--- of just 200 gm !! A razor =
sharp Agate edge would shatter easily. 
 
    Two bearing types which WILL take =
typical seismometer loads of several kg 
are a plane rolling on a ball - =
in my case a section of a SS scalpel blade on 
a SS ball bearing - and crossed =
cylinders. These can be hardened EN57 steel rod, 
or more usually tungsten carbide =
rods. Tungsten carbide needle roller bearings are 
produced. You can buy 1/8" =
OD tungsten carbide drills and use the shank ends, but 
there are plenty of small WC =
milling cutters with parallel shanks. I got a free 
supply of broken cutter shanks =
from a small engineering business just by asking ! 
 
=
    I described =
the test results of these and of rolling foil and wire very low =
dynamic loss, high load flexures =
in a paper in ArchivX. The traditional crossed 
foil and wire type suspensions =
show energy loss and noise due to the flexure 
being bent very close to the =
clamped ends. 
  
    Below is a photo of the seismometer =
that I use
http://www.jclahr.com/science/psn/chapman/2008=
%20lehman/index.html 
    I can set the period to 30 seconds =
quite easily to sense the Love 
waves at their full amplitude. =
The principle features are a SS scalpel 
blade rolling on a 1/2" SS =
ball bearing lower fulcrum. The V cable top 
support prevents the arm from =
rotating about it's long axis - this can 
produce an undamped peak at 3~8 =
Hz in the FFT display if it is not 
suppressed. The quad Neodymium =
magnet damping and sensor blocks are 
highly effective. A 1/16" =
thick horizontal Copper damping blade is used. 
Soft Aluminum can also be used, =
but it is significantly diamagnetic and 
has double the resistivity. It is =
also relatively difficult to buy. One 
advantage of this design is that =
the magnet block can be slid along the 
base bar to cover just as much of =
the N/S magnet joint as is required. 
This butted N/S magnet joint =
develops a much greater damping force than 
a widely spaced poles. The =
damping force required depends on the period 
of the arm as well as on the =
seismic mass. The sensor block uses 1.5" 
long magnets and a rectangular =
coil. This allows the arm to drift +/- 
1/2" without any change in =
the sensitivity. A relatively few number of 
turns is required on the coil - =
1,500 to 2,000. The sensitivity is about 
20x that of a traditional Alnico =
U magnet + relay coil. 
 
=
    A Manual for =
the commercial SEP UK school seismometer is at 
    http://www.mindsetsonline.co.uk/images/Seismom=
eter.pdf 
    The amplifier band pass is from =
0.016 to 5 Hz and the gain can be 
switched x100, x200 or x500. The =
UK is a crowded noisy island with very 
few local quakes, so a 5 Hz LP =
filter is optimal. The period is set by 
tilting the base plate and a =
value of 25 to 30 seconds is usually chosen. 
The suspension is 1/8" OD =
crossed tungsten carbide needle rollers. The 
mass is brass. The boom is ~56 cm =
long. The extended period traces enable 
you to pick up at least twice the =
number of quakes identified by a P&S 
wave trigger. You pick out the =
often large surface waves and then look 
for the P&S waves.  =
    This is a =
very successful project. Over 400 seismometers have been =
sold since Easter 2007. =
 
=
    Regards, =
 
=
    Chris Chapman =
MA Oxon (Physics-retired)