From: Ted Channel 
To: psnlist@..............
Subject: Re: Geophone Damping Mass Slew rate


This is kind of the same subject..................I understand you can dam=
pen a coil with a resistor, =20

Hi Ted,

    Correct
=20
Does anyone use this method in place of a Lehman style magnet plate?

    There are several disadvantages in doing this.
    You don't generally get a high enough output from a U Alnico magnet +=
 coil system. These systems are non linear with position drift,
    so the damping can vary quite a lot with offset drift. You want the da=
mping to be constant.
    Having a damping resistor across the coil usually lowers the voltage=
 output quite a lot. It also significantly increases the sensor noise.
    Resetting the damping also alters the voltage output. You want this to=
 be constant.

Do you give up anything (voltage) by using a resistor on the coil?

    Yes. Increased noise and the constant sensitivity.

If it works, why do we still use magnet plates to damp?

    Because that is a better and more easily controlled system.=20

    Regards,

    Chris










From: Ted Channel <tchannel@............>

To: psnlist@..............

Subject: Re: Geophone Damping Mass Slew rate







This is kind of the same subject.........=
..........I understand you can dampen a coil with a resistor,  =



 


Hi Ted,


 


    Correct


 


Does anyone use this method in place of=
 a Lehman style magnet plate?


 


    There are several disa=
dvantages in doing this.


    You don't generally get a high enough output from=
 a U Alnico magnet + coil system. These systems are non linear with positi=
on drift,


    so the damping can vary quite a lot with offset dr=
ift. You want the damping to be constant.


    Having a damping resistor across the coil usually=
 lowers the voltage output quite a lot. It also significantly increases th=
e sensor noise.


    Resetting the damping also alters the voltage outp=
ut. You want this to be constant.


 


Do you give up anything (voltage) by usin=
g a resistor on the coil?


 


    Yes. Increased noise and the constant sensitivity.=



 


If it works, why do we still use magnet=
 plates to damp?


 


    Because that is a better and more easily controlle=
d system. 


 


    Regards,


 


    Chris