In a message dated 2006/11/15, davewilley@............. writes:

> My question for you all is will there be any noticeable magnetic 
> interaction between the 3 units I need to worry about with stacking them about .25 - .5 
> inches apart inside the PVC tubing?

Hi Dave Willey,.

       The geophone units should have no magnetic interactions when stacked 
together. However, you do need to connect them fairly accurately at right 
angles
and they should be clamped in place. Can you provide an inner rod / tube of 
plastic and bore holes in this to mount / align the geophones?

       The 4.5 Hz geophones do have stray fields at both ends, but the barrel 
is the mild steel return path for the axially mounted central magnets. I 
would suggest a 1 cm spacing.

       You can get Roberts' type period extension amplifiers from 
www.sara.pg.it These should enable you to receive teleseismic P and S waves, which you 
won't otherwise see with 4.5 Hz geophones. See the note about 4.5 Hz geophones 
on Larry's website?

       When you have remounted the geophones, do make a record of the wire 
colours and that they are the correct way around for sensing E, N and UP signals 
with the correct polarity. Paint / Mark lines on the exterior of the case 
with the correct directions.

       Are you going to solder the metal film damping resistors and any RF 
capacitors across the geophone terminals? Remember to check the input resistance 
of your amplifier and use it in the calculation for the damping resistor. 

       How about protection diodes? Do you get severe thunder storms in your 
area? Is the soil sandy / rocky / dry? It is over many areas in the USA and 
this can give problems with local lightning. Your house and system may all be 
exposed many feet above the local 'Earth' conducting plane.

       The outer case must be hermetically sealed and the cable end also 
sealed. Some cable types allow air to pass through between the wires when under 
pressure. Also seal the amplifier end of the cable. I suggest that you add a bag 
of inert silica gel drying crystals inside the case to absorb any moisture. 

       Regards,

       Chris Chapman
       
In a me=
ssage dated 2006/11/15, davewilley@............. writes:



My question for you all is will=
 there be any noticeable magnetic interaction between the 3 units I need to=20=
worry about with stacking them about .25 - .5 inches apart inside the PVC tu=
bing?




Hi Dave Willey,.



       The geophone units should have no magne=
tic interactions when stacked together. However, you do need to connect them=
 fairly accurately at right angles

and they should be clamped in place. Can you provide an inner rod / tube of=20=
plastic and bore holes in this to mount / align the geophones?



       The 4.5 Hz geophones do have stray fiel=
ds at both ends, but the barrel is the mild steel return path for the axiall=
y mounted central magnets. I would suggest a 1 cm spacing.



       You can get Roberts' type period extens=
ion amplifiers from www.sara.pg.it These should enable you to receive telese=
ismic P and S waves, which you won't otherwise see with 4.5 Hz geophones. Se=
e the note about 4.5 Hz geophones on Larry's website?



       When you have remounted the geophones,=20=
do make a record of the wire colours and that they are the correct way aroun=
d for sensing E, N and UP signals with the correct polarity. Paint / Mark li=
nes on the exterior of the case with the correct directions.



       Are you going to solder the metal film=20=
damping resistors and any RF capacitors across the geophone terminals? Remem=
ber to check the input resistance of your amplifier and use it in the calcul=
ation for the damping resistor. 



       How about protection diodes? Do you get=
 severe thunder storms in your area? Is the soil sandy / rocky / dry? It is=20=
over many areas in the USA and this can give problems with local lightning.=20=
Your house and system may all be exposed many feet above the local 'Earth' c=
onducting plane.



       The outer case must be hermetically sea=
led and the cable end also sealed. Some cable types allow air to pass throug=
h between the wires when under pressure. Also seal the amplifier end of the=20=
cable. I suggest that you add a bag of inert silica gel drying crystals insi=
de the case to absorb any moisture. 



       Regards,



       Chris Chapman