PSN-L Email List Message

Subject: Re: Geophone Questions
From: ChrisAtUpw@.......
Date: Thu, 9 Nov 2006 16:21:25 EST


In a message dated 2006/11/09, davewilley@............. writes:

> Subj:Geophone Questions=20
> Date:2006/11/09 09:28:50 GMT Standard Time
> From:davewilley@.............
> I=E2=80=99ve got one of Larry=E2=80=99s geophone systems for detection jus=
t local activity.=20
>=20
> Maybe I=E2=80=99ll build a SG sensor later on.

Hi Dave,

       Unfortunately, Larry has stopped producing the SG boards, although th=
e=20
circuits are available.

> But for now, I=E2=80=99m now moving my geophone away from the house to out=
 back in=20
> an area that is relatively isolated...
> I am trying to come up with a container of some sort to house one of Larry=
=E2=80=99s=20
> 3 axis geophone, and some way to develop the  new site for the geophone.
>=20
> I=E2=80=99ve seen talk on controlling the temp in SG type sensors.  But no=
thing=20
> specific to 4.5 Hz geophones. =20

       You don't have to control the temperature of geophones. The SG=20
seismometer used diode detectors which drifted with temperature.

I=E2=80=99ve also heard talk on the list of folks burying the geophones in t=
he=20
ground.  So it=20
> would seem to me that I would not need to temp stabilize the geophone  if=20
> they are down 4 =E2=80=93 6 feet in the ground  So temperature stabilizati=
on of a=20
> geophone would be major overkill?

       Definitley NOT neccessary to control the temperature! Burying the=20
geophones can get ythem away from quite a bit of surface noise and it also s=
creens=20
for RFI.

> 8=E2=80=9D dia thick walled PVC water pipe and end caps are relatively eas=
y to=20
> obtain locally.  Any reason not to bury 4 =E2=80=93 6 feet of vertical pip=
e in the ground=20
> and place the geophone glued in the bottom of the cap?=20

       The tube needs to be completely sealed and a waterproof gland used fo=
r=20
the cable. Also seal the ends of the cable.=20
      =20
       Note that you have to mount the vertical geophone with the pins=20
DOWNWARD.

       The plastic geophone cases are about 5" OD by 3" high, but the wires=20
come out sideways. This can add an extra couple of inches or more. It is usu=
al=20
to seal the geophone case after filling with dry N2.

       You might consider mounting the geophone case inside a plastic tube=20
with both ends sealed, say about 1 ft long? Make alignment marks on the outs=
ide=20
of the tube corresponding to N and E. Then dig a hole with an auger over 3 f=
t=20
deep, put in the tube, align it and backfill with soil. You need a loop of=20
nylon rope attached around the tube so that you can retrieve it if necessary=
.. =20

> The geophone case itself is cracked and no longer waterproof.  So I am=20
> planning to make the PVC pipe waterproof   Will barometric pressure change=
s=20
> affect the geophone?=20

       Air pressure changes should not effect the geophones themselves -=20
their cases are hermetically sealed.

Should I allow air pressure to equalize by placing a small breath hole in th=
e=20
PVC at=20
> the top where the wires are located?

       NO. Seal it completely! Otherwise you will get condensation problems=20
and the chamber will quite slowly fill with water. Can you fill the sealed=20
chamber with dry gas / add a bag of silica gel crystals?=20

       If the seismometer is outside the house, you should add some=20
protection diodes to guard against lightning surges.

> Or does anyone have a better idea / suggestion as a way to develop a new=20
> site for a geophone?=20

       You can hire motor driven augers and extension arms for digging holes=
?=20


       Regards,

       Chris Chapman
In a me=
ssage dated 2006/11/09, davewilley@............. writes:

Subj:Geophone Questions =
Date:2006/11/09 09:28:50 GMT Standard Time
From:davewilley@.............
I=E2=80=99ve got one of Larry=E2=80=99s geophone systems for detection just=20= local activity.
Maybe I=E2=80=99ll build a SG sensor later on.


Hi Dave,

       Unfortunately, Larry has stopped produc= ing the SG boards, although the circuits are available.


But for now, I=E2=80=99m now mo= ving my geophone away from the house to out back in an area that is relative= ly isolated...
I am trying to come up with a container of some sort to house one of Larry= =E2=80=99s 3 axis geophone, and some way to develop the  new site for t= he geophone.

I=E2=80=99ve seen talk on controlling the temp in SG type sensors.  But= nothing specific to 4.5 Hz geophones. 


       You don't have to control the temperat= ure of geophones. The SG seismometer used diode detectors which drifted with= temperature.

I=E2=80=99ve also heard talk on the list of folks burying the geophones in t= he ground.  So it

would seem to me that I would=20= not need to temp stabilize the geophone  if they are down 4 =E2=80=93 6= feet in the ground  So temperature stabilization of a geophone would b= e major overkill?


       Definitley NOT neccessary to control t= he temperature! Burying the geophones can get ythem away from quite a bit of= surface noise and it also screens for RFI.

8=E2=80=9D dia thick walled PVC= water pipe and end caps are relatively easy to obtain locally.  Any re= ason not to bury 4 =E2=80=93 6 feet of vertical pipe in the ground and place= the geophone glued in the bottom of the cap?


       The tube needs to be completely sealed= and a waterproof gland used for the cable. Also seal the ends of the cable.=
      
       Note that you have to mount the vertica= l geophone with the pins DOWNWARD.

       The plastic geophone cases are about 5"= OD by 3" high, but the wires come out sideways. This can add an extra coupl= e of inches or more. It is usual to seal the geophone case after filling wit= h dry N2.

       You might consider mounting the geophon= e case inside a plastic tube with both ends sealed, say about 1 ft long? Mak= e alignment marks on the outside of the tube corresponding to N and E. Then=20= dig a hole with an auger over 3 ft deep, put in the tube, align it and backf= ill with soil. You need a loop of nylon rope attached around the tube so tha= t you can retrieve it if necessary. 


The geophone case itself is cra= cked and no longer waterproof.  So I am planning to make the PVC pipe w= aterproof   Will barometric pressure changes affect the geophone?=20=


       Air pressure changes should not effect= the geophones themselves - their cases are hermetically sealed.

Should I allow air pressure to equalize by placing a small breath hole in th= e PVC at

the top where the wires are lo= cated?


       NO. Seal it completely! Otherwise you=20= will get condensation problems and the chamber will quite slowly fill with w= ater. Can you fill the sealed chamber with dry gas / add a bag of silica gel= crystals?

       If the seismometer is outside the house= , you should add some protection diodes to guard against lightning surges.

Or does anyone have a better i= dea / suggestion as a way to develop a new site for a geophone?

       You can hire motor driven augers and ex= tension arms for digging holes?

       Regards,

       Chris Chapman

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