In a message dated 29/09/02, jandmarshall@............ writes:

> Please visit my web site www.cableone.net/jandmarshall and choose the 
> Seismic Page to view my project.
>  
> Problems I note right off
>     1 - I have a 4-5 hz oscillation in the pendulum.
>     2 - I seem to have a lot of environmental noise -- I can not correlate 
> it with actions in the house
>     

Hi Jan,

       The photos are a great help. 

       What is the weight of the seismic mass on the end of the arm?

       What undamped oscillation period are you getting?

       Only you can check the damping. Deflect the beam a very small amount, 
maybe by putting a screwdriver etc near it, let it go and observe it. The 
pendulum should swing back to the zero position, but it should not go beyond 
zero and come back, or show any actual oscillations.

       The bearings, general construction etc look fine. Check for electrical 
activity in the house / movement of magnetic materials, even cars / trains 
outside etc to search for the environmental noise. Does the seis react when 
the fridge / cooker / central heating switches on / off? It is more usual to 
put both magnets on the baseplate and the coil and damping plate on the arm. 
With unscreened magnets on the arm, it can and will pick up any small changes 
in the local environmental magnetic field.

       From the photos, I can't see where the pick up coil is in relation to 
it's magnet. The centre line of the coil should be roughly on the end face of 
the magnet with your setup. 

       The 5 Hz could be due to the whole arm system nodding up and down or 
side to side. Try tapping the end post with your finger and see if you get 
this sort of frequency response. With your coil system as shown, you will 
likely pick up both vertical and horizontal movements of the arm.

       What amplifier / filter / A/D system are you using? What is the 
cut-off frequency of the filter?

       Regards,

       Chris Chapman
In a message dated 29/09/02, jandmarshall@............ writes:



Please visit my web site www.cableone.net/jandmarshall and choose the Seismic Page to view my project.

 

Problems I note right off

    1 - I have a 4-5 hz oscillation in the pendulum.

    2 - I seem to have a lot of environmental noise -- I can not correlate it with actions in the house

    3 - Am I damped enough?



Hi Jan,



       The photos are a great help. 



       What is the weight of the seismic mass on the end of the arm?



       What undamped oscillation period are you getting?



       Only you can check the damping. Deflect the beam a very small amount, maybe by putting a screwdriver etc near it, let it go and observe it. The pendulum should swing back to the zero position, but it should not go beyond zero and come back, or show any actual oscillations.



       The bearings, general construction etc look fine. Check for electrical activity in the house / movement of magnetic materials, even cars / trains outside etc to search for the environmental noise. Does the seis react when the fridge / cooker / central heating switches on / off? It is more usual to put both magnets on the baseplate and the coil and damping plate on the arm. With unscreened magnets on the arm, it can and will pick up any small changes in the local environmental magnetic field.



       From the photos, I can't see where the pick up coil is in relation to it's magnet. The centre line of the coil should be roughly on the end face of the magnet with your setup. 



       The 5 Hz could be due to the whole arm system nodding up and down or side to side. Try tapping the end post with your finger and see if you get this sort of frequency response. With your coil system as shown, you will likely pick up both vertical and horizontal movements of the arm.



       What amplifier / filter / A/D system are you using? What is the cut-off frequency of the filter?



       Regards,



       Chris Chapman