PSN-L Email List Message

Subject: Re: Digest from 10/15/2009 00:01:59
From: ChrisAtUpw@.......
Date: Sun, 18 Oct 2009 20:51:20 EDT


 
_http://tinkeringcaveman.googlepages.com/home_ 
(http://tinkeringcaveman.googlepages.com/home) 
In a message dated 16/10/2009, kevin.mckee@....... writes:

>>    Perhaps one or both of my postings  weren't clear.
Hi Kevin,
 
    You say:
>> "Do your homework! A lot of folks out there have already done  this, 
save yourself time, effort, and money by doing some research." 
 
    Them why have you chosen to use a photo  transistor detector? This has 
over a hundred times the noise of a photo diode  detector and it seriously 
limits the performance.
 
 You say:
>>  "Be Patient! Patience is a necessary virtue for a  seismologist. It 
turns out that in my location near Washington D.C., there is  limited 
seismicity; I sometimes go for a month at a time without detecting  distant quakes."
 
    I also live in a quiet seismic area, but it is  a QUIET WEEK when I 
don't see TWO QUAKES. Call up the drumplot of a  local professional station to 
check what quakes you should see? 
 
>>    Because that temperature varies over  relatively long times, however, 
I judge that it is trivial after considering  that the ac-coupled 
integrator suppresses signals longer than about 20  seconds.
 
    You can see convective thermal  fluctuations with periods from just a 
few seconds  upwards. 

>>    Also, the instruments use  glass fibers for the torsion fiber. 
 
    You need to use a single fibre or wire  suspension. If you use a bundle 
of fibres there will be frictional effects in  the suspension which allow 
the zero position to wander from quake to  quake.

>>    I recognize that this instrument is not  a lab quality instrument, 
but for something that can be built so cheaply and  easily by anyone without a 
lot of technical or machining skills it's a very  useful device. I've 
detected at least 120 earthquakes from all over the world  with it. 

>>    Why discourage folks out there  who don't have the skills or $ to 
build a Porsche when a Ford will get the job  done, while spreading the fun of 
doing science?




Maybe because your 'design' does not seem  to be even in the model T Ford 
class? 
    
    The design seems to be mostly built inside a jar.  This increases the 
construction difficulty and is not neccessary. It would be a  lot easier to 
construct the mechanism on two or three disks connected by three  lengths of 
threaded rod. The completed and adjusted mechanism could  then be slid 
inside the glass jar. 
    How is the period set up, measured  and adjusted? How is the damping 
measured and adjusted to ~0.7  critical? Note that coins are a copper alloy, 
have a much higher electrical  resistance than pure copper and don't make 
such efficient dampers.
 
    I have no interest in trying to make a low  specification device. And I 
don't fancy the hassle of "The initial  set-up may take several hours, and 
then you need to monitor or record the output  for days or weeks to 
determine if you are getting adequate results."
 
    Amateur seismologists try to detect the same quakes  as the 
professionals and require similar low noise high performance systems. If  a seismic 
system does not work down to below the local seismic background noise,  it is a 
waste of time, effort and money. 
 
    This looks like it was based on a Wood  Anderson 0.8 second period 
seismometer  _    http://www.data.scec.org/Module/s3inset3.html_ 
(http://www.data.scec.org/Module/s3inset3.html)  
_    
http://www.eas.slu.edu/Earthquake_Center/Instruments/torsion_seis.html_ (http://www.eas.slu.edu/Earthquake_Center/Instruments/torsion_seis.html) 
 
    Regards,
 
    Chris Chapman





http://tinkeringcave= man.googlepages.com/home
In a message dated 16/10/2009, kevin.mckee@....... writes:
>>    Perhaps one or both of my= postings=20 weren't clear.
Hi Kevin,
 
    You say:
>> "Do your homework! A lot of folks out there have alread= y done=20 this, save yourself time, effort, and money by doing some research."
 
    Them why have you chosen to use a photo= =20 transistor detector? This has over a hundred times the noise of a photo di= ode=20 detector and it seriously limits the performance.
 
 You say:
>>  "Be Patient! Patience is a necessary virtue for= a=20 seismologist. It turns out that in my location near Washington D.C., there= is=20 limited seismicity; I sometimes go for a month at a time without detecting= =20 distant quakes."
 
    I also live in a quiet seismic area, but= it is=20 a QUIET WEEK when I don't see TWO QUAKES. Call up the drumplot of a=20 local professional station to check what quakes you should see? =
 
>>    Because that temperature vari= es over=20 relatively long times, however, I judge that it is trivial after consideri= ng=20 that the ac-coupled integrator suppresses signals longer than about 20=20 seconds.
 
    You can see convective thermal= =20 fluctuations with periods from just a few seconds=20 upwards. 

>>    Also, the instrument= s use=20 glass fibers for the torsion fiber.
 
    You need to use a single fibre or wir= e=20 suspension. If you use a bundle of fibres there will be frictional effects= in=20 the suspension which allow the zero position to wander from quake to=20 quake.

>>    I recognize that this instrument= is not=20 a lab quality instrument, but for something that can be built so cheaply= and=20 easily by anyone without a lot of technical or machining skills it's a ver= y=20 useful device. I've detected at least 120 earthquakes from all over the wo= rld=20 with it.

>>    Why discourage folks out= there=20 who don't have the skills or $ to build a Porsche when a Ford will get the= job=20 done, while spreading the fun of doing science?

 
    Maybe because your 'design' does not seem=20 to be even in the model T Ford class?
    
    The design seems to be mostly built inside a= jar.=20 This increases the construction difficulty and is not neccessary. It would= be a=20 lot easier to construct the mechanism on two or three disks connected by= three=20 lengths of threaded rod. The completed and adjusted mechanism co= uld=20 then be slid inside the glass jar. 
    How is the period set up, measured=20 and adjusted? How is the damping measured and adjusted to ~0.7=20 critical? Note that coins are a copper alloy, have a much higher elec= trical=20 resistance than pure copper and don't make such efficient dampers.
 
    I have no interest in trying to make a low=20 specification device. And I don't fancy the hassle of "The initi= al=20 set-up may take several hours, and then you need to monitor or record the= output=20 for days or weeks to determine if you are getting adequate results."
 
    Amateur seismologists try to detect the same= quakes=20 as the professionals and require similar low noise high performance system= s. If=20 a seismic system does not work down to below the local seismic background= noise,=20 it is a waste of time, effort and money.
 
    This looks like it was based on a Wood= =20 Anderson 0.8 second period seismometer     &= nbsp;http://www.data.scec.org/Module/s3inset3.html 
    http://www.eas.slu.edu/Earthquake_Center/Ins= truments/torsion_seis.html
 
    Regards,
 
    Chris Chapman

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