ChrisAtUpw@....... wrote:  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
       


ChrisAtUpw@....... wrote:  
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