In a message dated 24/12/2009, tchannel@............ writes:

Hi Folks,   I added a heat source,  light bulb, to the top area of my 
vault.   I could see at once this  was a big big help.   In this pit are three 
sensors, each has a  cover of some kind.

Hi Ted,
 
    I keep well away from light bulbs. They attract too  many insects, mice 
etc. This is just swapping one problem for several others.  Too much heat 
from a concentrated source like a light bulb can also be  noisy.
    
    I seal the seismometer covers. I buy a can of spray  grouting, roughly 
assemble the polystyrene sheet sides with tape, run a very wet  cloth over 
the insides of all joints, spray on the grouting, close the joints  with tape 
and use a paint scraper to remove excess foam. I then stick the top on  and 
tape it in place.
 
    DigiKey etc keep high power resistors in Aluminum  cases with bolt 
holes. I buy two of these and a high wattage wall-wort AC  transformer.  Bolt 
two resistors to Al sheet and mount inside the top of  each foam housing. You 
need maybe 10 watts each seismometer.

Ch 1 is a Lehman 20 seconds, covered with a large  Styrofoam box, not air 
tight, just some butt joints and a bit of tape.  (  no noise problems)
Ch 2 is 22 seconds, covered with a large  Styrofoam box, not air tight, no 
tape, butt  joints.     (big noise problems)  with  frequencies of 15 to 60 
seconds
Ch 3 is a vertical, housed in its own plastic  enclosure, fairly tight.  
(no noise problems) other than the high  frequencies stuff, which the vertical 
picks up.
 
I just added a heat source,inside the  pit, did a before and after, FFT on 
all three sensors, and see a big  improvement.   Especially on Ch 2, not 
much on the other  two.   I can email images.
 
I know this may not be the only issue, but it  made a 100% improvement.
 
To better explain this let me say the pit  4'x4'x6' lined with blocks.  
Along the top edge of the pit, I added 4" of  insulation batting.   On top of 
that I added 1" ridged Styrofoam  panels taped to form a lid.
I added bricks to compress all and form a tighter  lid.   The pit is under 
the house in the craw space, 24" from any  footing.  The crawl space seem 
quiet, I can not feel any air currents, no  wind blowing.
No duct work, blowing air.   No  temperature changes,  52 degrees for a low 
and 55 for a high, out side  pit, less inside the pit.

    Reverse convection / convection / draft noise  may be way, way below 
what you can feel. Check with smoke from a  cigarette?

Obviously, air must be circulating or otherwise  influencing into the 
bottom of the pit. The heat source in layering the  air in the pit, and 
minimizing the turbulence.

    Could this be just drafts? 

Any similar observation?  and or  advice.
 
I am surprised because I thought the boxes plus  lid, would do the job.   
Before I rework the boxes, taping,  insulating etc.   Perhaps I should 
address the lid and make it  thicker, from 1" to 6" batting, and improve the lid 
seal.   Maybe I  should do all of it.
 
I could also leave the heat source, especially if  that is the real fix.   

    I would make the individual boxes first. Can you  use a sheet of 
polythene to cover the top of the pit? Weight it down all around  with cloth tubes 
filled with sand?
 

    Regards,
 
    Chris Chapman





In a message dated 24/12/2009, tchannel@............ writes:

  
Hi Folks,   I added a heat so=
urce,=20
  light bulb, to the top area of my vault.   I could see at once=
 this=20
  was a big big help.   In this pit are three sensors, each has=
 a=20
  cover of some kind.
Hi Ted,
 
    I keep well away from light bulbs. They attra=
ct too=20
many insects, mice etc. This is just swapping one problem for several othe=
rs.=20
Too much heat from a concentrated source like a light bulb can also be=20
noisy.
    
    I seal the seismometer covers. I buy a can of=
 spray=20
grouting, roughly assemble the polystyrene sheet sides with tape, run a ve=
ry wet=20
cloth over the insides of all joints, spray on the grouting, close the joi=
nts=20
with tape and use a paint scraper to remove excess foam. I then stick the=
 top on=20
and tape it in place.
 
    DigiKey etc keep high power resistors in Alum=
inum=20
cases with bolt holes. I buy two of these and a high wattage wall-wort AC=
=20
transformer.  Bolt two resistors to Al sheet and mount inside the top=
 of=20
each foam housing. You need maybe 10 watts each seismometer.

  
Ch 1 is a Lehman 20 seconds, covered wi=
th a large=20
  Styrofoam box, not air tight, just some butt joints and a bit of tape.&n=
bsp; (=20
  no noise problems)
  
Ch 2 is 22 seconds, covered with a larg=
e=20
  Styrofoam box, not air tight, no tape, butt=20
  joints.     (big noise problems)  with=20
  frequencies of 15 to 60 seconds
  
Ch 3 is a vertical, housed in its own=
 plastic=20
  enclosure, fairly tight.  (no noise problems) other than the high=
=20
  frequencies stuff, which the vertical picks up.
  
 
  
I just added a heat source,inside the=
=20
  pit, did a before and after, FFT on all three sensors, and see a bi=
g=20
  improvement.   Especially on Ch 2, not much on the other=20
  two.   I can email images.
  
 
  
I know this may not be the only issue,=
 but it=20
  made a 100% improvement.
  
 
  
To better explain this let me say the=
 pit=20
  4'x4'x6' lined with blocks.  Along the top edge of the pit, I added=
 4" of=20
  insulation batting.   On top of that I added 1" ridged Styrofo=
am=20
  panels taped to form a lid.
  
I added bricks to compress all and form=
 a tighter=20
  lid.   The pit is under the house in the craw space, 24" from=
 any=20
  footing.  The crawl space seem quiet, I can not feel any air curren=
ts, no=20
  wind blowing.
  
No duct work, blowing air.  =
 No=20
  temperature changes,  52 degrees for a low and 55 for a high, out=
 side=20
  pit, less inside the pit.
    Reverse convection / convection / draft noise=
=20
may be way, way below what you can feel. Check with smoke from=
 a=20
cigarette?

  
Obviously, air must be circulating or=
 otherwise=20
  influencing into the bottom of the pit. The heat source in layering=
 the=20
  air in the pit, and minimizing the turbulence.
    Could this be just drafts? 

  
Any similar observation?  and or=
=20
  advice.
  
 
  
I am surprised because I thought the bo=
xes plus=20
  lid, would do the job.   Before I rework the boxes, taping,=20
  insulating etc.   Perhaps I should address the lid and make it=
=20
  thicker, from 1" to 6" batting, and improve the lid seal.   Ma=
ybe I=20
  should do all of it.
  
 
  
I could also leave the heat source, esp=
ecially if=20
  that is the real fix.   
    I would make the individual boxes first. Can=
 you=20
use a sheet of polythene to cover the top of the pit? Weight it down all=
 around=20
with cloth tubes filled with sand?
 

    Regards,
 
    Chris Chapman