In a message=20=
dated 18/10/05, charles.r.patton@........ writes:
Hi Charles,
Thanks.=20
We have been experimenting with use=
d BIC pens. The medium size is fitted with a 1mm tungsten carbide ball and a=
convenient cylindrical brass holder. They clean up with meths quite nicely=20=
and extend the rundown of a pendulum by about a factor of x10 over a 2 thou=20=
brass foil suspension. Adding some light clock oil extends the period quite=20=
a bit further.=20
McMaster also carry SS and Carbide=20=
balls and Carbide rods. Crossed cylinder carbide suspensions are also good.
Regards,
Chris Chapman
Subject: Crossed rod hinge/suspensions
From: meredith lamb paleoartifact@.........
Date: Tue, 18 Oct 2005 20:15:22 -0600
Hi Chris, and all,
I'd think that a crossed rod hinge might be a vast improvement for one or
more
"hinges" on about any "garden gate" horizontal, or, for a vertical
seismometers
lower hinges; or, for a "S-G" hanging pendulum. It all depends on how you
need to orientate two of the three rods for the specific seismometer being
designed for; or, to replace the existing hinges on such.
Just to be sure we're on the same setup plain...I can visualize; say, a ro=
d
running straight horizontally (like across this page), and one can then
introduce two rods underneath the horizontal rod, on the outer extremes tha=
t
can go up and down (top to bottom of this page). The horizontal rod would
have a centered "boom" attached that leads to the mass. One would then
either have a wire (for a hanging gate horizontal), or a spring for a
vertical. On
a S-G of course, the boom/mass would just hang down. Of course, a vertical
would (likely) need two such hinges on the bottom hinge area...and it could
be possible to have the angled upper hinge of the same crossed rod design.
Have never tried crossed rods as such, but, I'd think it might be as good
as a
ball bearing hinge design...and likely without near as much mechanical
adjustments fuss; as a ball bearing hinge can need. In many ways I think;
this crossed rod hinge is quite similar to ball bearings suspensions, as th=
e
small contact area is similar. The best forced offset of the mass for
harmonic
motions in timed trials I've seen (table top/edge test) for ball bearings o=
n
a
variety of contact surfaces (without dampening), was about 6 hours. Too me,
the longer a mass oscillates (without dampening); that means the hinge/
suspension has less friction, and thus the mass's enertia would be more
sensitive to external local earth movements.
....................................
For a S-G like, hanging pendulum (horizontal sensing), I'd think you
previously
mentioned zero torque suspension (zts) would be far more sensitive or
friction
free, but it is abit harder to build. As you know...via emails and alot of
your
generous help; the current table top/edge experiments here with that trial
suspension, can freely oscillate up to 10-11 hours on average. My old S-G
with its two thin straight hanging suspension strips, would only oscillate
(without dampening), up to 35 minutes.
Can heartily agree now, with your stressing trying new hinges, whether it
be
ball bearings, crossed rods, or the zero torque suspension, as they will al=
l
have alot less friction, as opposed to the older, pointed boom pivot
(horizontal)
razor edge boom pivot (vertical), or simply hanging strips of metal like on
a
S-G (horizontal), that create alot more friction/torque sensitivity
limitations
in the hinge/suspension contact area/medium which affects the mass enertia
response to stay in one place "in space", while the earth moves.
Take care, Meredith
Hi Chris, and all,
I'd think that a crossed rod hinge might be a vast improvement for one=
or more
"hinges" on about any "garden gate" horizontal, or=
, for a vertical seismometers
lower hinges; or, for a "S-G" hanging pendulum. It all=
depends on how you
need to orientate two of the three rods for the specific seismometer b=
eing
designed for; or, to replace the existing hinges on such.
Just to be sure we're on the same setup plain...I can visualize; say, =
a rod
running straight horizontally (like across this page), and one can the=
n
introduce two rods underneath the horizontal rod, on the outer extreme=
s that
can go up and down (top to bottom of this page). The horizontal =
rod would
have a centered "boom" attached that leads to the mass. =
; One would then
either have a wire (for a hanging gate horizontal), or a spring for a =
vertical. On
a S-G of course, the boom/mass would just hang down. Of course, =
a vertical
would (likely) need two such hinges on the bottom hinge area...and it =
could
be possible to have the angled upper hinge of the same crossed rod des=
ign.
Have never tried crossed rods as such, but, I'd think it might be as g=
ood as a
ball bearing hinge design...and likely without near as much mechanical=
adjustments fuss; as a ball bearing hinge can need. In many ways=
I think;
this crossed rod hinge is quite similar to ball bearings suspensions, =
as the
small contact area is similar. The best forced offset of the mas=
s for harmonic
motions in timed trials I've seen (table top/edge test) for ball beari=
ngs on a
variety of contact surfaces (without dampening), was about 6 hours.&nb=
sp; Too me,
the longer a mass oscillates (without dampening); that means the hinge=
/
suspension has less friction, and thus the mass's enertia would be mor=
e
sensitive to external local earth movements.
....................................
For a S-G like, hanging pendulum (horizontal sensing), I'd think you p=
reviously
mentioned zero torque suspension (zts) would be far more sensitive or =
friction
free, but it is abit harder to build. As you know...via emails a=
nd alot of your
generous help; the current table top/edge experiments here with that t=
rial
suspension, can freely oscillate up to 10-11 hours on average. M=
y old S-G
with its two thin straight hanging suspension strips, would only oscil=
late
(without dampening), up to 35 minutes.
Can heartily agree now, with your stressing trying new hinges, whether=
it be
ball bearings, crossed rods, or the zero torque suspension, as they wi=
ll all
have alot less friction, as opposed to the older, pointed boom pivot (=
horizontal)
razor edge boom pivot (vertical), or simply hanging strips of metal li=
ke on a
S-G (horizontal), that create alot more friction/torque sensitivity li=
mitations
in the hinge/suspension contact area/medium which affects the mass ene=
rtia
response to stay in one place "in space", while the earth mo=
ves.
Take care, Meredith
Subject: Re: good leveling screw source
From: "Charles R. Patton" charles.r.patton@........
Date: Tue, 18 Oct 2005 21:48:24 -0700
I know Angel and others are talking about micrometers for leveling
screws -- but any micrometer I'm familiar with only has 40 TPI, not a
lot better than a 10/32 screw, and the screw is a lot cheaper, that's
why I suggested some of the metric screws with 0.25 pitch (101.6 TPI).
The laser adjustment screws are generally in the 80 TPI range with some
in the 100 TPI class, but they are generally $20 or more, whiile the
metric screws can be put together for a dollar or two.
Today I was talking to my machinist friend, and he gets one inch
micrometers for $10 from
Industrial Tool Sales in Costa Mesa, California Phone:
949-631-1586. These micrometers have tungsten faces and are made in
China. They look great. He may be getting a bit of a price break as
they buy a lot of tooling, but nevertheless, that is still a very low
price, and is the lowest price I know of.
Regards,
Charles Patton
Larry P Thomas wrote:
>How about adapting (modifying) a cheap micrometer as an adjustment screw.
>Should 100 tpi and would have a nice knurled handle to turn. Just an idea.
>It may not end up any cheaper.
>
>Later,
>Larry P. Thomas, wa0gwa
>
>Imagine it/Achieve it --- Dream it/Become it
>Larry P. Thomas, wa0gwa 1 913 244-8761
>Krell Technologies (http://www.krell.com)
>PO BOX 3565, OLATHE, KS 66063-3565 USA
>
>
>
>-----Original Message-----
>From: psn-l-request@.............. [mailto:psn-l-request@............... On
>Behalf Of Mark Robinson
>Sent: Tuesday, October 18, 2005 5:54 AM
>To: psn-l@..............
>Subject: Re: good leveling screw source
>
>Angel wrote:
>
>
>>Hello,
>>
>>I have spent a good hour looking on the web for some nice leveling
>>screws with no luck. Does anyone on the list have a source.
>>
>>Something with a high thread count and a point so the thing does not
>>walk when you turn it.
>>
>>
>
>Roger's post got my head working.
>
>Have a look at some old carburettors at a car wreckers.
>
>I was always impressed by the flame adjustment screws in old Bic Flic
>lighters, but they seem to be unobtanium in NZ these days.
>
>Mark
>
>__________________________________________________________
>
>Public Seismic Network Mailing List (PSN-L)
>
>To leave this list email PSN-L-REQUEST@.............. with
>the body of the message (first line only): unsubscribe
>See http://www.seismicnet.com/maillist.html for more information.
>
>__________________________________________________________
>
>Public Seismic Network Mailing List (PSN-L)
>
>To leave this list email PSN-L-REQUEST@.............. with
>the body of the message (first line only): unsubscribe
>See http://www.seismicnet.com/maillist.html for more information.
>
>
>
>
>
__________________________________________________________
Public Seismic Network Mailing List (PSN-L)
Subject: Re: good leveling screw source
From: "James Hannon" jmhannon@.........
Date: Wed, 19 Oct 105 07:33:38 CDT
I have not found the need to use extra fine pitch screws for leveling. I use national fine pitch socket head screws and grind the end to a dome shape. By using a long handle allen wrench to turn the screws I can get all the fineness in the adjustment I need.
Jim Hannon
--
Jim Hannon
http://www.fmtcs.com/web/jmhannon/
42,11.90N,91,39.26W
WB0TXL
--
__________________________________________________________
Public Seismic Network Mailing List (PSN-L)
Subject: RE: good leveling screw source
From: "Jack Ivey" ivey@..........
Date: Wed, 19 Oct 2005 08:39:24 -0400
The nice thing about micrometer barrels is that that they
have more precise tolerances, bigger diameter threads and=20
a longer threaded contact area than a screw/nut=20
combination, so they will have much less radial play in the
shaft. This makes anything you are supporting with them=20
more stable. If you can avoid depending on the screw for
horizontal location of the piece you are supporting, that=20
might not be an issue.
Jack
-----Original Message-----
From: psn-l-request@.............. [mailto:psn-l-request@...............
On Behalf Of Charles R. Patton
Sent: Wednesday, October 19, 2005 12:48 AM
To: psn-l@..............
Subject: Re: good leveling screw source
I know Angel and others are talking about micrometers for leveling=20
screws -- but any micrometer I'm familiar with only has 40 TPI, not a=20
lot better than a 10/32 screw, and the screw is a lot cheaper, that's=20
why I suggested some of the metric screws with 0.25 pitch (101.6 TPI). =20
The laser adjustment screws are generally in the 80 TPI range with some=20
in the 100 TPI class, but they are generally $20 or more, whiile the=20
metric screws can be put together for a dollar or two.=20
Today I was talking to my machinist friend, and he gets one inch=20
micrometers for $10 from
Industrial Tool Sales in Costa Mesa, California Phone: =20
949-631-1586. These micrometers have tungsten faces and are made in=20
China. They look great. He may be getting a bit of a price break as=20
they buy a lot of tooling, but nevertheless, that is still a very low=20
price, and is the lowest price I know of.
Regards,
Charles Patton
Larry P Thomas wrote:
>How about adapting (modifying) a cheap micrometer as an adjustment
screw.
>Should 100 tpi and would have a nice knurled handle to turn. Just an
idea.
>It may not end up any cheaper.
>
>Later,
>Larry P. Thomas, wa0gwa
>
>Imagine it/Achieve it --- Dream it/Become it
>Larry P. Thomas, wa0gwa 1 913 244-8761
>Krell Technologies (http://www.krell.com)
>PO BOX 3565, OLATHE, KS 66063-3565 USA=20
>
> =20
>
>-----Original Message-----
>From: psn-l-request@..............
[mailto:psn-l-request@............... On
>Behalf Of Mark Robinson
>Sent: Tuesday, October 18, 2005 5:54 AM
>To: psn-l@..............
>Subject: Re: good leveling screw source
>
>Angel wrote:
> =20
>
>>Hello,
>>
>>I have spent a good hour looking on the web for some nice leveling
>>screws with no luck. Does anyone on the list have a source.
>>
>>Something with a high thread count and a point so the thing does not
>>walk when you turn it.
>> =20
>>
>
>Roger's post got my head working.
>
>Have a look at some old carburettors at a car wreckers.
>
>I was always impressed by the flame adjustment screws in old Bic Flic
>lighters, but they seem to be unobtanium in NZ these days.
>
>Mark
>
>__________________________________________________________
>
>Public Seismic Network Mailing List (PSN-L)
>
>To leave this list email PSN-L-REQUEST@.............. with=20
>the body of the message (first line only): unsubscribe
>See http://www.seismicnet.com/maillist.html for more information.
>
>__________________________________________________________
>
>Public Seismic Network Mailing List (PSN-L)
>
>To leave this list email PSN-L-REQUEST@.............. with=20
>the body of the message (first line only): unsubscribe
>See http://www.seismicnet.com/maillist.html for more information.
>
>
>
> =20
>
__________________________________________________________
Public Seismic Network Mailing List (PSN-L)
__________________________________________________________
Public Seismic Network Mailing List (PSN-L)
Subject: Re: good leveling screw source
From: ChrisAtUpw@.......
Date: Wed, 19 Oct 2005 10:42:45 EDT
In a message dated 18/10/05, charles.r.patton@........ writes:
> Chris,
> Your're right -- apparently frames or some such. So, anyway, got to
> McMaster-Carrs site http://www.mcmaster.com/ and enter :
> 91800A087 in the "FIND" box for the screws
> 91828A006 in the "FIND" box for the nuts
Hi Charles,
Thanks. Sorry for the slow response.
Found them OK, but what size of seismometer are you thinking about?
The screws are 1.2 mm OD = 0.047" and the length is 10 mm = 0.394"
> I know Angel and others are talking about micrometers for leveling screws
> -- but any micrometer I'm familiar with only has 40 TPI, not a lot better than
> a 10/32 screw, and the screw is a lot cheaper, that's why I suggested some
> of the metric screws with 0.25 pitch (101.6 TPI). The laser adjustment screws
> are generally in the 80 TPI range with some in the 100 TPI class, but they
> are generally $20 or more, while the metric screws can be put together for a
>
For light apparatus I can use SS Socket Cap 4 mm OD with a 2.5 mm
ball, which is 36.3 TPI and max 1.38" long. For Lehmans and the like, I use 6 mm
OD with a 5 mm ball, which is 25.4 TPI and max 1.97" long. McMaster do not seem
to stock either lengths in SS. The big ++ so far as I am concerned is that
you can cover a small hole in the top of your Celotex box with sticky tape and
use this to intoduce a hex driver to adjust the levelling screws. I keep the
tension in the mounting bolt using a second nut on the top of the baseplate and
wavy washer. This effectively removes any 'slop' in the threads.
The A2 grade SS range of socket caps can be centre drilled in the end
with a carbide bit and some oil. I made myself a couple of centre locating
attachments. In a lathe, I drilled a small central hole in a short length of hex
bar to match the pilot of a centre drill. Then I drilled and blind tapped the
other end to 4 or 6mm. I clamp the bolt vertically, screw on the centring
tube, start the pilot hole using the centre drill, remove the centring tube and
finish boring to get a 90 deg cone to hold the ball.
However as I mentioned in a previous note, you can get rotating ball
end and swivel end socket cap screws for McMC. You can also buy a range of
'thumb screws'.
I also buy zinc plated mild steel 6 mm set screws / bolts up to 60 mm
long. (or 1/4" by 2.1/2" long.) These are very convenient for mounting the two
1/4" mild steel backing plates for a quad NdFeB variable magnetic damping
attachment, using three nuts with each screw. Being mild steel, they 'short out'
most of any stray field due to the powerful magnets.
Regards,
Chris Chapman
In a message=20=
dated 18/10/05, charles.r.patton@........ writes:
Chris,
Your're right -- apparently frames or some such. So, anyway, got to=20
McMaster-Carrs site http://www.mcmaster.com/ and enter :
91800A087 in the "FIND" box for the screws
91828A006 in the "FIND" box for the nuts
Hi Charles,
Thanks. Sorry for the slow response=
.
Found them OK, but what size of sei=
smometer are you thinking about?
The screws are 1.2 mm OD =3D 0.047"=
and the length is 10 mm =3D 0.394"
I know Angel and others are=
talking about micrometers for leveling screws -- but any micrometer I'm fam=
iliar with only has 40 TPI, not a lot better than a 10/32 screw, and the scr=
ew is a lot cheaper, that's why I suggested some of the metric screws with 0=
..25 pitch (101.6 TPI). The laser adjustment screws are generally in th=
e 80 TPI range with some in the 100 TPI class, but they are generally $20 or=
more, while the metric screws can be put together for a dollar or two.
For light apparatus I can use SS So=
cket Cap 4 mm OD with a 2.5 mm ball, which is 36.3 TPI and max 1.38" long. F=
or Lehmans and the like, I use 6 mm OD with a 5 mm ball, which is 25.4 TPI a=
nd max 1.97" long. McMaster do not seem to stock either lengths in SS. The b=
ig ++ so far as I am concerned is that you can cover a small hole in the top=
of your Celotex box with sticky tape and use this to intoduce a hex driver=20=
to adjust the levelling screws. I keep the tension in the mounting bolt usin=
g a second nut on the top of the baseplate and wavy washer. This effectively=
removes any 'slop' in the threads.
The A2 grade SS range of socket cap=
s can be centre drilled in the end with a carbide bit and some oil. I made m=
yself a couple of centre locating attachments. In a lathe, I drilled a small=
central hole in a short length of hex bar to match the pilot of a centre dr=
ill. Then I drilled and blind tapped the other end to 4 or 6mm. I clamp the=20=
bolt vertically, screw on the centring tube, start the pilot hole using the=20=
centre drill, remove the centring tube and finish boring to get a 90 deg con=
e to hold the ball.
However as I mentioned in a p=
revious note, you can get rotating ball end and swivel end socket cap screws=
for McMC. You can also buy a range of 'thumb screws'.
I also buy zinc plated mild steel 6 mm se=
t screws / bolts up to 60 mm long. (or 1/4" by 2.1/2" long.) These are very=20=
convenient for mounting the two 1/4" mild steel backing plates for a quad Nd=
FeB variable magnetic damping attachment, using three nuts with each screw.=20=
Being mild steel, they 'short out' most of any stray field due to the powerf=
ul magnets.
Regards,
Chris Chapman
Subject: seis. book on ebay
From: BOB BARNS royb1@...........
Date: Thu, 20 Oct 2005 10:55:33 -0400
Hi gang,
QUANTITATIVE SEISMOLOGY, Vol 1, Aki & Richards
Item number: 6983765423 ends Oct. 24
A classic although Vol. 2 contains info on seismometers.
Bob
__________________________________________________________
Public Seismic Network Mailing List (PSN-L)
Subject: Re: good leveling screw source
From: Dave Willey davewilley@.............
Date: Thu, 20 Oct 2005 18:10:50 -0700 (PDT)
Larry,
Since you got me thinking about using a micrometer for
seismo leveling adjustments, why not just buy the head
instead of hacking up a full micrometer?
For example:
McMaster-Carr online catalog - Pg 2080 has
Starrett and Mitutoyo Micrometer Heads.
I've used these heads for graduated adjustment on test
jig leveling in the lab for optics and other
lightweight uses.
My only worry is the weight of the seismo itself that
the mic head will have to support.
One other point I should also make. Somebody ELSE paid
the bill. Some of them are not cheap!)
Dave Willey - KD6KWM
> Larry P Thomas wrote:
>
> >How about adapting (modifying) a cheap micrometer
> as an adjustment screw.
> >Should 100 tpi and would have a nice knurled handle
> to turn. Just an idea.
> >It may not end up any cheaper.
> >
> >Later,
> >Larry P. Thomas, wa0gwa
__________________________________________________________
Public Seismic Network Mailing List (PSN-L)
Subject: Re: good leveling screw source
From: ChrisAtUpw@.......
Date: Thu, 20 Oct 2005 21:45:58 EDT
In a message dated 21/10/05, davewilley@............. writes:
> Larry,
> Since you got me thinking about using a micrometer for seismo leveling
> adjustments, why not just buy the head instead of hacking up a full micrometer?
>
> I've used these heads for graduated adjustment on test jig leveling in the
> lab for optics and other lightweight uses. My only worry is the weight of the
> seismo itself that the mic head will have to support. Somebody ELSE paid the
> bill.
> Dave Willey - KD6KWM
Hi Dave,
I just checked EBAY for 'Micrometer Head'. There are 19 listed at the
moment, some starting from $5. I bought two 1" ones a while back and paid
about $8 each.
If you get a bit of tube the same ID as the OD of the rod and a
matching SS bearing, you can make a good 'ball point' which doesn't wander. You can
usually tighten the thread on a micrometer.
Regards,
Chris Chapman
In a message=20=
dated 21/10/05, davewilley@............. writes:
Larry,
Since you got me thinking about using a micrometer for seismo leveling a=
djustments, why not just buy the head instead of hacking up a full micromete=
r?
I've used these heads for graduated adjustment on test jig leveling in t=
he lab for optics and other lightweight uses. My only worry is the weight of=
the seismo itself that the mic head will have to support. Somebody ELSE pai=
d the bill.=20
Dave Willey - KD6KWM
Hi Dave,
I just checked EBAY for 'Micrometer=
Head'. There are 19 listed at the moment, some starting from $5. I bought t=
wo 1" ones a while back and paid about $8 each.=20
If you get a bit of tube the same I=
D as the OD of the rod and a matching SS bearing, you can make a good 'ball=20=
point' which doesn't wander. You can usually tighten the thread on a microme=
ter.
Regards,
Chris Chapman
Subject: [Fwd: Horizontal Pendulum]
From: Larry Cochrane lcochrane@..............
Date: Fri, 21 Oct 2005 23:36:52 -0700
-------- Original Message --------
Subject: Horizontal Pendulum
Date: Fri, 21 Oct 2005 20:33:15 -0400
From: KATHRYN ROBERTS
To: Larry Cochrane
Larry, thank you for your reply. The PSN-L@............... did not work. (i don't
have good computer skills.) Would you post this on the list? i'm new to the list and
seismology. i've enjoying reading the posts and have been thinking about a horizontal
pendulum Lehman type seismo using metal shims (what is the best material for shims
and best thickness?) Anyway, the horizontal pendulum would be supported by shims
above and below the pendulum that are ninety degrees perpendicular to the horizontal
axis of the pendulum. The upper shim would be attached to the 'mast' and then to a
tube or rod that is attached to the pendulum, again with the linear axis will be
perpendicular to the pendulum's horizontal plane. This would place the upper shim in
tension. The lower shim is also placed in tension by attaching the end away from the
coil to the above mentioned tube or pipe that is attached to the pendulum. The lower
shim will run away from the mast towards the coil. One thing that will have to be
determined is the position were the upper and lower tubes join the pendulum. The
tubes' positions would determine the flex positon of the shims, hopefully to be able
to find the point of greatest flexion of the shims with the lowest torque needed to
cause the flex or bending of the shim. Have many people tried this? How did it work?
Thanks, geofffrey roberts, Crystal River, Florida
__________________________________________________________
Public Seismic Network Mailing List (PSN-L)
Subject: Laboratory of earthquake's prediction.
From: Alexandr Yagodin midia@..............
Date: Sat, 22 Oct 2005 09:03:45 +0200
Hi to all!
The prediction of earthquakes more, than for 2 hours prior to the beginning. This problem is technically solved.
We have lead tests from one station, have received good results.
http://www.tectonica.pochta.ru/recenzia.htm -
This review the doctor of geology is received in the period, when I had instead of the gauge - animals.
http://www.tectonica.pochta.ru/protocol.htm - The protocol of tests of system of earthquake's prediction.
But two years the government does not give money, though even at session of a commission Knesset on a science 20/07/05 it was considered.
I am ready to present it for any commission in Haifa. If there will be a financing - any more there will be no victims from earthquakes and tsunami.
Yours faithfully to all of you.
Laboratory of earthquake's prediction. Haifa.
Yagodin Alexandr
+972-4-8598143 (rus)
(http://www.seu.ru/members/earthquakes)
midia@..............
Hi to all!
The prediction of earthquakes more, than for 2 hours prior to the beginning.
This problem is technically solved.
We have lead tests from one station, have received good results.
http://www.tectonica.pochta.ru/recenzia.htm
-
This review the doctor of geology is received in the period, when I had
instead of the gauge - animals.
http://www.tectonica.pochta.ru/protocol.htm -
The protocol of
tests of system of earthquake’s prediction.
But two years the government does not give money, though even at session of a
commission Knesset on a science 20/07/05 it was considered.
I am ready to present it for any commission in Haifa. If there will be a
financing - any more there will be no victims from earthquakes and tsunami.
Yours faithfully to all of you.
Laboratory of earthquake's prediction. Haifa.
Yagodin Alexandr
+972-4-8598143 (rus)
(http://www.seu.ru/members/earthquakes)
midia@..............
Subject: Re: Horizontal Pendulum]
From: "Connie and Jim Lehman" lehmancj@...........
Date: Sat, 22 Oct 2005 10:43:03 -0400
Geoffery--Thanks for your interest in seismology and the "Lehman horizontal"
design. I am puzzled a bit by your use of "shims"-- my idea of shims has
been only in work demanding small changes in distance--like leveling a
table, or a piece of scientific apparatus. The usual shims in precision
work are sheets of metal with so many l/1000ths of an inch in
thickness--otherwise known as mills} Since the seismo base is a tripod--
(for stability) shim material can be used to balance and level the system.
I am not sure what version of sensor plans you are following, but I
suggest that you keep construction simple with a wire hinge at the top, and
a knife edge on the boom end. After you get that working with a 15-20 sec
free swing, properly damped, you can refine and modify your design as you
like. To get a good "garden gate" swing the upper wire hinge (tensional)
should be about 1/4th inch off the vertical with the compressional knife
edge.
Best wishes, Jim
----- Original Message -----
From: "Larry Cochrane"
To:
Sent: Saturday, October 22, 2005 2:36 AM
Subject: [Fwd: Horizontal Pendulum]
>
> -------- Original Message --------
> Subject: Horizontal Pendulum
> Date: Fri, 21 Oct 2005 20:33:15 -0400
> From: KATHRYN ROBERTS
> To: Larry Cochrane
>
> Larry, thank you for your reply. The PSN-L@............... did not work.
(i don't
> have good computer skills.) Would you post this on the list? i'm new to
the list and
> seismology. i've enjoying reading the posts and have been thinking about a
horizontal
> pendulum Lehman type seismo using metal shims (what is the best material
for shims
> and best thickness?) Anyway, the horizontal pendulum would be supported
by shims
> above and below the pendulum that are ninety degrees perpendicular to the
horizontal
> axis of the pendulum. The upper shim would be attached to the 'mast' and
then to a
> tube or rod that is attached to the pendulum, again with the linear axis
will be
> perpendicular to the pendulum's horizontal plane. This would place the
upper shim in
> tension. The lower shim is also placed in tension by attaching the end
away from the
> coil to the above mentioned tube or pipe that is attached to the pendulum.
The lower
> shim will run away from the mast towards the coil. One thing that will
have to be
> determined is the position were the upper and lower tubes join the
pendulum. The
> tubes' positions would determine the flex positon of the shims, hopefully
to be able
> to find the point of greatest flexion of the shims with the lowest torque
needed to
> cause the flex or bending of the shim. Have many people tried this? How
did it work?
> Thanks, geofffrey roberts, Crystal River, Florida
>
> __________________________________________________________
>
> Public Seismic Network Mailing List (PSN-L)
>
> To leave this list email PSN-L-REQUEST@.............. with
> the body of the message (first line only): unsubscribe
> See http://www.seismicnet.com/maillist.html for more information.
>
__________________________________________________________
Public Seismic Network Mailing List (PSN-L)
Subject: Re: Horizontal Pendulum]
From: "KATHRYN ROBERTS" KROBERTS23@...............
Date: Sat, 22 Oct 2005 12:28:12 -0400
hi, thanks for the reply. You are right about shims being used to level
things, etc. Some of the home built vertical pendulums use shims as a
hinge. i want to use shims as hinges for the horizontal pendulum. The shim
idea is to reduce friction and maximize the torque applied to the base/frame
by earth motion. Although i have not been able to describe the design on
paper, i have been able to draw the plans. One (of many) problems: will the
shim material be strong enough to support the pendulum? geofffry<><
----- Original Message -----
From: "Connie and Jim Lehman"
To:
Sent: Saturday, October 22, 2005 10:43 AM
Subject: Re: Horizontal Pendulum]
> Geoffery--Thanks for your interest in seismology and the "Lehman
> horizontal"
> design. I am puzzled a bit by your use of "shims"-- my idea of shims has
> been only in work demanding small changes in distance--like leveling a
> table, or a piece of scientific apparatus. The usual shims in precision
> work are sheets of metal with so many l/1000ths of an inch in
> thickness--otherwise known as mills} Since the seismo base is a tripod--
> (for stability) shim material can be used to balance and level the
> system.
> I am not sure what version of sensor plans you are following, but I
> suggest that you keep construction simple with a wire hinge at the top,
> and
> a knife edge on the boom end. After you get that working with a 15-20 sec
> free swing, properly damped, you can refine and modify your design as you
> like. To get a good "garden gate" swing the upper wire hinge (tensional)
> should be about 1/4th inch off the vertical with the compressional knife
> edge.
> Best wishes, Jim
>
> ----- Original Message -----
> From: "Larry Cochrane"
> To:
> Sent: Saturday, October 22, 2005 2:36 AM
> Subject: [Fwd: Horizontal Pendulum]
>
>
>>
>> -------- Original Message --------
>> Subject: Horizontal Pendulum
>> Date: Fri, 21 Oct 2005 20:33:15 -0400
>> From: KATHRYN ROBERTS
>> To: Larry Cochrane
>>
>> Larry, thank you for your reply. The PSN-L@............... did not work.
> (i don't
>> have good computer skills.) Would you post this on the list? i'm new to
> the list and
>> seismology. i've enjoying reading the posts and have been thinking about
>> a
> horizontal
>> pendulum Lehman type seismo using metal shims (what is the best material
> for shims
>> and best thickness?) Anyway, the horizontal pendulum would be
>> supported
> by shims
>> above and below the pendulum that are ninety degrees perpendicular to the
> horizontal
>> axis of the pendulum. The upper shim would be attached to the 'mast'
>> and
> then to a
>> tube or rod that is attached to the pendulum, again with the linear axis
> will be
>> perpendicular to the pendulum's horizontal plane. This would place the
> upper shim in
>> tension. The lower shim is also placed in tension by attaching the end
> away from the
>> coil to the above mentioned tube or pipe that is attached to the
>> pendulum.
> The lower
>> shim will run away from the mast towards the coil. One thing that will
> have to be
>> determined is the position were the upper and lower tubes join the
> pendulum. The
>> tubes' positions would determine the flex positon of the shims, hopefully
> to be able
>> to find the point of greatest flexion of the shims with the lowest torque
> needed to
>> cause the flex or bending of the shim. Have many people tried this? How
> did it work?
>> Thanks, geofffrey roberts, Crystal River, Florida
>>
>> __________________________________________________________
>>
>> Public Seismic Network Mailing List (PSN-L)
>>
>> To leave this list email PSN-L-REQUEST@.............. with
>> the body of the message (first line only): unsubscribe
>> See http://www.seismicnet.com/maillist.html for more information.
>>
>
> __________________________________________________________
>
> Public Seismic Network Mailing List (PSN-L)
>
> To leave this list email PSN-L-REQUEST@.............. with
> the body of the message (first line only): unsubscribe
> See http://www.seismicnet.com/maillist.html for more information.
__________________________________________________________
Public Seismic Network Mailing List (PSN-L)
Subject: 15 to 20 second free swing
From: "KATHRYN ROBERTS" KROBERTS23@...............
Date: Sat, 22 Oct 2005 13:21:30 -0400
Hi, is the 15 to 20 second free swing dampened? Or does 'free' mean
undampener? Please remember i am new to all this. Thanks, geofff<><
----- Original Message -----
From: "Connie and Jim Lehman"
To:
Sent: Saturday, October 22, 2005 10:43 AM
Subject: Re: Horizontal Pendulum]
> Geoffery--Thanks for your interest in seismology and the "Lehman
> horizontal"
> design. I am puzzled a bit by your use of "shims"-- my idea of shims has
> been only in work demanding small changes in distance--like leveling a
> table, or a piece of scientific apparatus. The usual shims in precision
> work are sheets of metal with so many l/1000ths of an inch in
> thickness--otherwise known as mills} Since the seismo base is a tripod--
> (for stability) shim material can be used to balance and level the
> system.
> I am not sure what version of sensor plans you are following, but I
> suggest that you keep construction simple with a wire hinge at the top,
> and
> a knife edge on the boom end. After you get that working with a 15-20 sec
> free swing, properly damped, you can refine and modify your design as you
> like. To get a good "garden gate" swing the upper wire hinge (tensional)
> should be about 1/4th inch off the vertical with the compressional knife
> edge.
> Best wishes, Jim
>
> ----- Original Message -----
> From: "Larry Cochrane"
> To:
> Sent: Saturday, October 22, 2005 2:36 AM
> Subject: [Fwd: Horizontal Pendulum]
>
>
>>
>> -------- Original Message --------
>> Subject: Horizontal Pendulum
>> Date: Fri, 21 Oct 2005 20:33:15 -0400
>> From: KATHRYN ROBERTS
>> To: Larry Cochrane
>>
>> Larry, thank you for your reply. The PSN-L@............... did not work.
> (i don't
>> have good computer skills.) Would you post this on the list? i'm new to
> the list and
>> seismology. i've enjoying reading the posts and have been thinking about
>> a
> horizontal
>> pendulum Lehman type seismo using metal shims (what is the best material
> for shims
>> and best thickness?) Anyway, the horizontal pendulum would be
>> supported
> by shims
>> above and below the pendulum that are ninety degrees perpendicular to the
> horizontal
>> axis of the pendulum. The upper shim would be attached to the 'mast'
>> and
> then to a
>> tube or rod that is attached to the pendulum, again with the linear axis
> will be
>> perpendicular to the pendulum's horizontal plane. This would place the
> upper shim in
>> tension. The lower shim is also placed in tension by attaching the end
> away from the
>> coil to the above mentioned tube or pipe that is attached to the
>> pendulum.
> The lower
>> shim will run away from the mast towards the coil. One thing that will
> have to be
>> determined is the position were the upper and lower tubes join the
> pendulum. The
>> tubes' positions would determine the flex positon of the shims, hopefully
> to be able
>> to find the point of greatest flexion of the shims with the lowest torque
> needed to
>> cause the flex or bending of the shim. Have many people tried this? How
> did it work?
>> Thanks, geofffrey roberts, Crystal River, Florida
>>
>> __________________________________________________________
>>
>> Public Seismic Network Mailing List (PSN-L)
>>
>> To leave this list email PSN-L-REQUEST@.............. with
>> the body of the message (first line only): unsubscribe
>> See http://www.seismicnet.com/maillist.html for more information.
>>
>
> __________________________________________________________
>
> Public Seismic Network Mailing List (PSN-L)
>
> To leave this list email PSN-L-REQUEST@.............. with
> the body of the message (first line only): unsubscribe
> See http://www.seismicnet.com/maillist.html for more information.
__________________________________________________________
Public Seismic Network Mailing List (PSN-L)
Subject: Re: Horizontal Pendulum]
From: ChrisAtUpw@.......
Date: Sat, 22 Oct 2005 15:04:44 EDT
In a message dated 22/10/05, KROBERTS23@............... writes:
> Some of the home built vertical pendulums use shims as a
> hinge. I want to use shims as hinges for the horizontal pendulum. The shim
> idea is to reduce friction and maximize the torque applied to the base/frame
> by earth motion. Although I have not been able to describe the design on
> paper, I have been able to draw the plans. One (of many) problems: will the
> shim material be strong enough to support the pendulum? geoffry<><
Hi there Geoffrey,
You try to use about 2 thou thick foil. Beryllium Copper, phosphor
bronze, hard bronze and stainless steel are all satisfactory. Brass may be less
satisfactory. Pure copper and Aluminum are not strong enough.
Two types of foil hinge may be used, usually both in tension. The
'Cardan' hinge is just vertical strips of foil clamped between two plates each
side, maybe 1/16" to 1/8" apart. The crossed foil hinge joins the cut away
corners of two square rods, see http://www.bryantlabs.net/seismo.html or
http://www.eas.slu.edu/People/STMorrissey/index.html click on 'photos and report'. These
particular hinges are for vertical seismometers, but the same principles apply
to horizontal types.
The 60 degree 'knife edges' used on chemical balances actually had a
rounded edge - they were not actually 'sharp' - and they worked fine for light
loads. Trying to use either a point in a cup or a metal cutting blade on a
flat give huge contact forces and are likely to limit the performance of a
seismometer, later if not immediatly.
Have a look at http://www.jclahr.com/science/psn/cor_psn.html for a
Lehman with single wire suspensions.
Regards,
Chris Chapman
In a message=20=
dated 22/10/05, KROBERTS23@............... writes:
Some of the home built ver=
tical pendulums use shims as a=20
hinge. I want to use shims as hinges for the horizontal pendulum. The sh=
im=20
idea is to reduce friction and maximize the torque applied to the base/f=
rame=20
by earth motion. Although I have not been able to describe the des=
ign on=20
paper, I have been able to draw the plans. One (of many) problems: will=20=
the=20
shim material be strong enough to support the pendulum? geoffry<=
;><
Hi there Geoffrey,
You try to use about 2 thou thick f=
oil. Beryllium Copper, phosphor bronze, hard bronze and stainless steel are=20=
all satisfactory. Brass may be less satisfactory. Pure copper and Aluminum a=
re not strong enough.
Two types of foil hinge may be used=
, usually both in tension. The 'Cardan' hinge is just vertical strips of foi=
l clamped between two plates each side, maybe 1/16" to 1/8" apart. The cross=
ed foil hinge joins the cut away corners of two square rods, see http://www.=
bryantlabs.net/seismo.html or http://www.eas.slu.edu/People/STMorrissey/inde=
x.html click on 'photos and report'. These particular hinges are for vertica=
l seismometers, but the same principles apply to horizontal types.
The 60 degree 'knife edges' u=
sed on chemical balances actually had a rounded edge - they were not actuall=
y 'sharp' - and they worked fine for light loads. Trying to use either a poi=
nt in a cup or a metal cutting blade on a flat give huge contact forces and=20=
are likely to limit the performance of a seismometer, later if not immediatl=
y.
Have a look at http://www.jclahr.co=
m/science/psn/cor_psn.html for a Lehman with single wire suspensions.=20
Regards,
Chris Chapman
Subject: Re: 15 to 20 second free swing
From: ChrisAtUpw@.......
Date: Sat, 22 Oct 2005 15:08:54 EDT
In a message dated 22/10/05, KROBERTS23@............... writes:
> Hi, is the 15 to 20 second free swing dampened? Or does 'free' mean
>
Hi there,
This is the free undamped swing period. Correctly damped, the arm
shoud not oscillate. Consider using magnetic damping. You are much more likely to
get satisfactory results than trying to use oil.
Regards,
Chris Chapman
In a message=20=
dated 22/10/05, KROBERTS23@............... writes:
Hi, is the 15 to 20 second=20=
free swing dampened? Or does 'free' mean=20
undampener? Please remember i am new to all this. Thanks, geofff
Hi there,
This is the free undamped swing per=
iod. Correctly damped, the arm shoud not oscillate. Consider using magnetic=20=
damping. You are much more likely to get satisfactory results than trying to=
use oil.
Regards,
Chris Chapman
Subject: Re: 15 to 20 second free swing
From: "Connie and Jim Lehman" lehmancj@...........
Date: Sat, 22 Oct 2005 18:49:06 -0400
HELLO AGAIN-- Yes the 15 to 20 second free swing is dampened. When set up
& stabilized, a horizontal system free swing would oscillate for hours and
give no definition to an event should one pass. It is a bit of a challenge
to get damping right--but looks easy once you've been through it. Somewhere
between free swing and critical damping(ie. no motion at all) is a
satisfactory zone. Think of it as a ratio--let's say 5 to l. When the
system has stabilized with a natural swing desired--there should be an
equilibrum position or a stable zero point. Displace the pendulum 10 mm,
release it and the pendulum should (with proper damping) overshoot the zero
point by 2 mm. --that is 5 to l. I have usually tuned my sensors to 8:l
ratio.--there is some leeway here. As Chris suggests, use magnetic damping
rather than liquid/vane if possible. Magnetic damping adjusts so
easily--like a piece of cake.
Best Wishes, Jim
----- Original Message -----
From: "KATHRYN ROBERTS"
To:
Sent: Saturday, October 22, 2005 1:21 PM
Subject: 15 to 20 second free swing
> Hi, is the 15 to 20 second free swing dampened? Or does 'free' mean
> undampener? Please remember i am new to all this. Thanks, geofff<><
> ----- Original Message -----
> From: "Connie and Jim Lehman"
> To:
> Sent: Saturday, October 22, 2005 10:43 AM
> Subject: Re: Horizontal Pendulum]
>
>
> > Geoffery--Thanks for your interest in seismology and the "Lehman
> > horizontal"
> > design. I am puzzled a bit by your use of "shims"-- my idea of shims
has
> > been only in work demanding small changes in distance--like leveling a
> > table, or a piece of scientific apparatus. The usual shims in precision
> > work are sheets of metal with so many l/1000ths of an inch in
> > thickness--otherwise known as mills} Since the seismo base is a tripod--
> > (for stability) shim material can be used to balance and level the
> > system.
> > I am not sure what version of sensor plans you are following, but I
> > suggest that you keep construction simple with a wire hinge at the top,
> > and
> > a knife edge on the boom end. After you get that working with a 15-20
sec
> > free swing, properly damped, you can refine and modify your design as
you
> > like. To get a good "garden gate" swing the upper wire hinge
(tensional)
> > should be about 1/4th inch off the vertical with the compressional knife
> > edge.
> > Best wishes, Jim
> >
> > ----- Original Message -----
> > From: "Larry Cochrane"
> > To:
> > Sent: Saturday, October 22, 2005 2:36 AM
> > Subject: [Fwd: Horizontal Pendulum]
> >
> >
> >>
> >> -------- Original Message --------
> >> Subject: Horizontal Pendulum
> >> Date: Fri, 21 Oct 2005 20:33:15 -0400
> >> From: KATHRYN ROBERTS
> >> To: Larry Cochrane
> >>
> >> Larry, thank you for your reply. The PSN-L@............... did not
work.
> > (i don't
> >> have good computer skills.) Would you post this on the list? i'm new to
> > the list and
> >> seismology. i've enjoying reading the posts and have been thinking
about
> >> a
> > horizontal
> >> pendulum Lehman type seismo using metal shims (what is the best
material
> > for shims
> >> and best thickness?) Anyway, the horizontal pendulum would be
> >> supported
> > by shims
> >> above and below the pendulum that are ninety degrees perpendicular to
the
> > horizontal
> >> axis of the pendulum. The upper shim would be attached to the 'mast'
> >> and
> > then to a
> >> tube or rod that is attached to the pendulum, again with the linear
axis
> > will be
> >> perpendicular to the pendulum's horizontal plane. This would place the
> > upper shim in
> >> tension. The lower shim is also placed in tension by attaching the end
> > away from the
> >> coil to the above mentioned tube or pipe that is attached to the
> >> pendulum.
> > The lower
> >> shim will run away from the mast towards the coil. One thing that will
> > have to be
> >> determined is the position were the upper and lower tubes join the
> > pendulum. The
> >> tubes' positions would determine the flex positon of the shims,
hopefully
> > to be able
> >> to find the point of greatest flexion of the shims with the lowest
torque
> > needed to
> >> cause the flex or bending of the shim. Have many people tried this? How
> > did it work?
> >> Thanks, geofffrey roberts, Crystal River, Florida
> >>
> >> __________________________________________________________
> >>
> >> Public Seismic Network Mailing List (PSN-L)
> >>
> >> To leave this list email PSN-L-REQUEST@.............. with
> >> the body of the message (first line only): unsubscribe
> >> See http://www.seismicnet.com/maillist.html for more information.
> >>
> >
> > __________________________________________________________
> >
> > Public Seismic Network Mailing List (PSN-L)
> >
> > To leave this list email PSN-L-REQUEST@.............. with
> > the body of the message (first line only): unsubscribe
> > See http://www.seismicnet.com/maillist.html for more information.
>
> __________________________________________________________
>
> Public Seismic Network Mailing List (PSN-L)
>
> To leave this list email PSN-L-REQUEST@.............. with
> the body of the message (first line only): unsubscribe
> See http://www.seismicnet.com/maillist.html for more information.
>
__________________________________________________________
Public Seismic Network Mailing List (PSN-L)
Subject: Re: 15 to 20 second free swing
From: "Geoff" gmvoeth@...........
Date: Sat, 22 Oct 2005 22:52:42 -0700
Hello Jim;
I do not mean to butt in it is just I am following
somewhat the things you say here and I want to
clarify a point on damping.
Until now I have been judging damping in
cycles of 360 degrees meaning I judge my
damping by looking only at the positive or
negative half cycle.
Say I let loose with a large swing on the positive
half cycle I will then measure the first and
second negative swings and get my damping
from those two peak values.
Say it swings ten divisions and then 360 degrees later
it swings one division
I then say my damping is 10:1.
I have been told by a Geophysicist named
Willis Jacobs at Golden Colorado
that a 10:1 damping is desirable to shoot for.
Any comments in regard to this ?
gmvoeth
----- Original Message -----
From: "Connie and Jim Lehman"
To:
Sent: Saturday, October 22, 2005 3:49 PM
Subject: Re: 15 to 20 second free swing
__________________________________________________________
Public Seismic Network Mailing List (PSN-L)
Subject: Re: 15 to 20 second free swing
From: "Connie and Jim Lehman" lehmancj@...........
Date: Sun, 23 Oct 2005 06:33:36 -0400
Hello Geoff--The 360 Degree technique sounds good here. A 10:1 ratio no
doubt is an ideal. I guess when you get "tighter" than that, an event
readout is compressed in size. It would be neat (for comparison purposes)
to be able to have different ratios exhibited by the same sensor on the same
event!! Thanks--Jim
----- Original Message -----
From: "Geoff"
To:
Sent: Sunday, October 23, 2005 1:52 AM
Subject: Re: 15 to 20 second free swing
> Hello Jim;
>
> I do not mean to butt in it is just I am following
> somewhat the things you say here and I want to
> clarify a point on damping.
>
> Until now I have been judging damping in
> cycles of 360 degrees meaning I judge my
> damping by looking only at the positive or
> negative half cycle.
>
> Say I let loose with a large swing on the positive
> half cycle I will then measure the first and
> second negative swings and get my damping
> from those two peak values.
>
> Say it swings ten divisions and then 360 degrees later
> it swings one division
> I then say my damping is 10:1.
>
> I have been told by a Geophysicist named
> Willis Jacobs at Golden Colorado
> that a 10:1 damping is desirable to shoot for.
>
> Any comments in regard to this ?
>
> gmvoeth
>
> ----- Original Message -----
> From: "Connie and Jim Lehman"
> To:
> Sent: Saturday, October 22, 2005 3:49 PM
> Subject: Re: 15 to 20 second free swing
>
> __________________________________________________________
>
> Public Seismic Network Mailing List (PSN-L)
>
> To leave this list email PSN-L-REQUEST@.............. with
> the body of the message (first line only): unsubscribe
> See http://www.seismicnet.com/maillist.html for more information.
>
__________________________________________________________
Public Seismic Network Mailing List (PSN-L)
Subject: Re: 15 to 20 second free swing
From: ChrisAtUpw@.......
Date: Sun, 23 Oct 2005 09:01:43 EDT
In a message dated 23/10/05, lehmancj@........... writes:
> Subj:Re: 15 to 20 second free swing
> From: lehmancj@........... (Connie and Jim Lehman)
>
> Hello Geoff--The 360 Degree technique sounds good here. A 10:1 ratio no
> doubt is an ideal. I guess when you get "tighter" than that, an event
> readout is compressed in size. It would be neat (for comparison purposes)
> to be able to have different ratios exhibited by the same sensor on the same
> event!! Thanks--Jim
Hi Geoff,
There is a basic misunderstanding here. You look at successive half
swings to define the damping. Say you deflect the boom gently to 10 mm and
release it. The 10:1 would give you a movement past zero to 1 mm. This should be
about right. It should then return to zero, but without going through zero for
another swing!
If you are getting two or more swings, you are seriously underdamped.
If you look at an underdamped response, it is flat for the higher
frequencies, then rises to a peak and then falls off very fast. Call
http://www.geospacelp.com/c_hs10.shtml The A curve is underdamped, The B curve is about
what we are looking for. You usually aim for about 70 to 80% of CRITICAL damping
- the critical damping response is curve C.
If your seismometer is seriously underdamped, sure it will give a
bigger signal, but this will only relate to it's OWN oscillatory characteristic,
NOT to the ground motion that you want to measure. The output only starts to
fall seriously when the seismometer is overdamped.
See http://www.jclahr.com/science/psn/wbauer/damped/d.htm for a
seismometer applet that gives a range of characteristics that you can choose. Read
to the bottom of
http://www.jclahr.com/science/psn/epics/links.html#Seismometer%20Basics to get typical values.
Regards,
Chris Chapman
> ----- Original Message -----
> From: "Geoff"
> Subject: Re: 15 to 20 second free swing
>
> > I do not mean to butt in it is just I am following somewhat the things you
> say here and I want to clarify a point on damping.
> >
> > Until now I have been judging damping in cycles of 360 degrees meaning I
> judge my damping by looking only at the positive or negative half cycle.
> > Say I let loose with a large swing on the positive half cycle I will then
> measure >the first and second negative swings and get my damping from those
> two peak >values.
> >
> > Say it swings ten divisions and then 360 degrees later it swings one
> division
> > I then say my damping is 10:1.
> >
> > I have been told by a Geophysicist named Willis Jacobs at Golden Colorado
> > that a 10:1 damping is desirable to shoot for.
> > Any comments in regard to this?
> >
In a message=20=
dated 23/10/05, lehmancj@........... writes:
Subj:Re: 15 to 20 second=
free swing
From: lehmancj@........... (Connie and Jim Lehman)
Hello Geoff--The 360 Degree technique sounds good here. A 10:1 ratio no
doubt is an ideal. I guess when you get "tighter" than that, an event
readout is compressed in size. It would be neat (for comparison purposes=
)
to be able to have different ratios exhibited by the same sensor on the=20=
same
event!! Thanks--Jim
Hi Geoff,
There is a basic misunderstanding h=
ere. You look at successive half swings to define the damping. Say you defle=
ct the boom gently to 10 mm and release it. The 10:1 would give you a moveme=
nt past zero to 1 mm. This should be about right. It should then r=
eturn to zero, but without going through zero for another swing!
If you are getting two or more swin=
gs, you are seriously underdamped.=20
If you look at an underdamped re=
sponse, it is flat for the higher frequencies, then rises to a peak and then falls off very fast. Call http://www.geospacelp.com/c_hs10.shtml=
The A curve is underdamped, The B curve is about what we are looking for. Y=
ou usually aim for about 70 to 80% of CRITICAL damping - the critical dampin=
g response is curve C.=20
If your seismometer is seriously un=
derdamped, sure it will give a bigger signal, but this will only relate to <=
U>it's OWN oscillatory characteristic, NOT to the ground motion that=20=
you want to measure. The output only starts to fall seriously when the s=
eismometer is overdamped.
See http://www.jclahr.com/science/p=
sn/wbauer/damped/d.htm for a seismometer applet that gives a range of charac=
teristics that you can choose. Read to the bottom of http://www.jclahr.com/s=
cience/psn/epics/links.html#Seismometer%20Basics to get typical values.
Regards,
Chris Chapman
----- Original Message -=
----
From: "Geoff" <gmvoeth@...........>
Subject: Re: 15 to 20 second free swing
> I do not mean to butt in it is just I am following somewhat the thi=
ngs you say here and I want to clarify a point on damping.
>
> Until now I have been judging damping in cycles of 360 degrees mean=
ing I judge my damping by looking only at the positive or negative half cycl=
e.
> Say I let loose with a large swing on the positive half cycle I wil=
l then measure >the first and second negative swings and get my damping f=
rom those two peak >values.
>
> Say it swings ten divisions and then 360 degrees later it swings on=
e division
> I then say my damping is 10:1.
>
> I have been told by a Geophysicist named Willis Jacobs at Gol=
den Colorado=20
> that a 10:1 damping is desirable to shoot for.
> Any comments in regard to this?
> gmvoeth
Subject: Re: 15 to 20 second free swing
From: Mauro Mariotti mariotti@.........
Date: Sun, 23 Oct 2005 21:35:10 +0200
Hi Larry,
The WinQuake Help reports the possibility to open the GSE2.0 data format.
Do WinQuake open compressed GSE2.0 data (CM6, CM5 etc...) ?
The format GSE2.0 usually starst with the strings:
WID2 ....
STA2...
DAT2...
datas...
CHK2...
do you mean that WinQUake will accept only data file containing:
BEGIN GSE2.0
WID2...
STA2...
DAT2...
....
is it correct?
Where I can find the editing syntax of the STATIONS.GS2 format ?
Best Regards
Mauro
WinQuake uses the keyword "BEGIN GSE2.0" to see if a file is in the
GSE2.0 format. This keyword must be within the first 512 bytes of the
file. WinQuake supports both single and multiple seismograms in one
GSE2.0 file. If there is more than one seismogram in a file, it will
be treated the same way as a PEPP or SEED volume data set.
The text file STATIONS.GS2 must be in the same directory as the
WinQuake program file (winqk32.exe). This file is used to lookup
station latitude and longitude information.
__________________________________________________________
Public Seismic Network Mailing List (PSN-L)
Subject: Crossed rod hinge/suspensions v/s ball bearings hinge/suspensions
From: meredith lamb paleoartifact@.........
Date: Sun, 23 Oct 2005 14:53:29 -0600
Hi all,
Chris Chapman recently stated in a private email that he thought a crossed
rod hinge
suspension would have less friction/dampening than a ball bearing
hinge...and he is
so very right!
Too visualize a crossed rod hinge: Imagine two spaced rods running up and
down this
page. Now; you introduce a horizontal rod centered across the other two
rods, and this
is the inge suspension rod that you hook up your boom/wire too. The crossed
rod hinge
suspension looks like the capitalized letter "H". You can visually rotate
the assembly
to make the hinge center rod workable for your desired horizontal or
vertical instrument.
Of course, for the hanging pendulum (S-G), the rod assembly is simply place=
d
flat atop
a mast, and the center rod oscillates/rotates atop the two outer rods. For
most horizontal
or vertical seismometers use, the assemblys two rods are placed against the
mast, (you
might need acouple here) and the center rod presses against these two rods
via a boom.
Its possible to use the same hinge for angled horizontal or vertical top of
the mast pivots
also. There is NO gouged or filed slot/s in any rods to hold the position o=
f
the crossed
rod; as that would ruin its lesser friction hinge or suspension purpose.
In my new view...I'd even go so far as to say; ball bearings
hinges/suspensions are
less ideal for most seismometers as they do have a noted problem with highe=
r
friction
for very small rotational displacements, whereas, crossed rod
hinges/suspensions have
less friction in this critical displacement area. Other hinge designs like
razors, points,
cardans (typical S-G hinge), shims etc., are so bad for contact friction,
torque/material
self dampening, that I'll not even consider or recommend their use again.
I've ran many hanging pendulum (S-G like), table top/edge tests with a
variety of ball
bearings on various contact surfaces in the last few weeks. The purpose of
the tests
was to estimate the friction of the various test models; via offsetting the
pendulum a
set distance, and simply timing how long the pendulum will continue
oscillating till it
visually quits moving. Ball bearings were visually observed to be rather
consistently
prone to stop in a shorter time where the displacement of the mass got down
to ~1//16"
deflection (from zero) oscillations...and usually stopped in a hour or two.
The
oscillations times with ball bearings ranged from 5 to 6 hours.
In the last few days, I tried acouple different rod materials in a crossed
rod hinge
with the same general table top/edge test platform. The first model, used 3
rods of what
I believe is grade 304 stainless steel 1/4" diameter rods. That oscillation=
s
test ran on
for ~8 hours. The second model used two drill rod shanks (clean round end),
with the
same stainless steel rod hinge across them, and that ran for ~7.5 hours.
Small mass
displacements decay oscillations on the descending order of 1/16", can go o=
n
for
several hours thereafter till the mass stops. While there is alot of
different material
that could be tested; I think its very obvious from just these 2 tests, thi=
s
this specific
type hinge is very much the better choice.
There is another hinge suspension, that has yielded longer oscillations
decay times
that I've worked with, and that is the Zero Torque Suspension. Those models
on the
same table top/edge tests, gave a range of 10-11 hours. However, I think
amateurs
will find that crossed rod hinge/suspensions will be easier to work with,
and its more
adoptable for *all* hinge situations like on a typical horizontal or
vertical seismometer,
whereas a zero torque suspension might reasonably only be good for a hangin=
g
pendulum (S-G).
Credit is given to Chris Chapman for suggesting trials of these various
suspensions
and guidance!
Take care, Meredith Lamb
Hi all,
Chris Chapman recently stated in a private email that he thought a cro=
ssed rod hinge
suspension would have less friction/dampening than a ball bearing hing=
e...and he is
so very right!
Too visualize a crossed rod hinge: Imagine two spaced rods runni=
ng up and down this
page. Now; you introduce a horizontal rod centered across t=
he other two rods, and this
is the inge suspension rod that you hook up your boom/wire too. =
The crossed rod hinge
suspension looks like the capitalized letter "H". You =
can visually rotate the assembly
to make the hinge center rod workable for your desired horizontal or v=
ertical instrument.
Of course, for the hanging pendulum (S-G), the rod assembly is simply =
placed flat atop
a mast, and the center rod oscillates/rotates atop the two outer =
rods. For most horizontal
or vertical seismometers use, the assemblys two rods are placed agains=
t the mast, (you
might need acouple here) and the center rod presses against these two =
rods via a boom.
Its possible to use the same hinge for angled horizontal or vertical t=
op of the mast pivots
also. There is NO gouged or filed slot/s in any rods to hold the=
position of the crossed
rod; as that would ruin its lesser friction hinge or suspension p=
urpose.
In my new view...I'd even go so far as to say; ball bearings hinges/su=
spensions are
less ideal for most seismometers as they do have a noted problem =
with higher friction
for very small rotational displacements, whereas, crossed rod hinge