PSN-L Message - Subject: Re: Geophone Damping Mass Slew rate

--- On Thu, 12/16/10, Ted Channel wrote: From: Ted Channel Subject: Re: Geophone Damping Mass Slew rate To: psnlist@.............. Date: Thursday, December 16, 2010, 12:11 PM =0A=0A =0A =0A=0AThis is kind of the same subject..................I =0Aund= erstand you can dampen a coil with a resistor,=A0 =0A=A0=0ADoes anyone use = this method in place of a Lehman =0Astyle magnet plate? I have for 20 years= and =0ADo you give up anything (voltage) by using a =0Aresistor on the coil?My = coil measures about 10 k ohms and I use about 1 k for critical damping. I d= on't lose any sensitivity =0AIf it works, why do we still use magnet plates to =0Adamp? It works so w= ell, I don't know why it isn't more popular. Pete Rowe =0A=A0=0AThanks, Ted=0A=0A ----- Original Message ----- =0A From: =0A Ch= ristopher =0A Chapman =0A To: psnlist@.............. =0A Sent: Thursday,= December 16, 2010 10:00 =0A AM=0A Subject: Re: Geophone Damping Mass Sle= w =0A rate=0A =20 =0A =0A =0A =0A =0A =0A =0A =0A =0A =0A =0A I =0A have been pla= ying around with a dismantled SPZ geophone damping and find=A0if you short = =0A the leads to the coil and then drop the mass=A0 the =0A mass will descend slowly, I guess from meeting=A0the generator cur= rent =0A being dissipated by the=A0internal =0A resistance.=A0 =A0 Questions arise from =0A this.=A0 =A0 1. if there were no internal resistance =0A (superconductor)=A0=A0 then wh= en the leads are shorted the mass would =0A fall=A0 =A0 a bit then stay forever hovering =0A ?=A0 =A0 =A0=A0=A0 Correct=0A =A0=0A 2.the =0A geophone is acting just like a rot= ating electrical generator=A0 armature developing =0A torque under electrical loads ?=A0 =A0 =A0=A0=A0 Correct=0A =A0=0A 3. =0A It seems to me that seismic noise rar= ely hits the resonant =0A frequency and=A0 =A0 you might do better to not =0A increase the damping over what already= =A0 =A0 is =0A there in the mechanical and physical sense ?=0A =A0=0A =A0=A0= =A0 No. The critical damping allows you to get=A0an =0A output voltage fla= t with frequency above the resonant =0A frequency.=A0 =A0 4. Does the rate at which the geophone =0A mass drop under heavy damping= =A0represent some new fundamental Eigen frequency?=0A =20 =A0=A0=A0=A0No. The resonance is determined by the mass of =0A the armatur= e and the spring constant. =A0=0A =A0=0A 5. =0A Can anyone provide me wi= th high school math=A0models which represent the mechanical =0A and=A0elec= trical behaviors of the geophone?=A0 =A0 High school math being trig and =0A algebra=A0minus the calculus?=0A = =A0=0A =A0=A0=A0 The theory is freely available on the =0A Internet.=0A = =A0=0A an Eigen freq not contained in EQ signals =0A then do no damping a= t all?=A0 This [little damping] should =0A work for weak EQ signals and not close = =0A strong ones ?=A0=0A =A0=0A =A0=A0=A0=A0=A0 An undamped geophone has = a single =0A frequency peaked response - definitely NOT what you want!=A0 = =0A =20 =A0=A0=A0=A0 Regards,=0A =A0=0A =A0=A0=A0=A0 Chris =0A Chapman=0A=0A=0A = <=

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--- On Thu, 12/16/10, Ted Channel = <tchannel@............> wrote:

From: Ted Channel <tchannel@............>
Subject: Re: Geopho= ne Damping Mass Slew rate
To: psnlist@..............
Date: Thursday, = December 16, 2010, 12:11 PM

=0A=0A =0A =0A=0A
This is kind of the sa= me subject..................I =0Aunderstand you can dampen a coil with a re= sistor,
=0A
&= nbsp;
=0A
Does anyone use this met= hod in place of a Lehman =0Astyle magnet plate? I have for 20 years and
=0A
Do you give up anything (voltage) by using a =0Ar= esistor on the coil?My coil measur= es about 10 k ohms and I use about 1 k for critical damping. I don't lose a= ny sensitivity
=0A
If it works, why do we still use magnet plates to =0Adamp? It works so well, I don't know why it isn't m= ore popular.
Pete Rowe
=0A

=0A
Th= anks, Ted
=0A
=0A
----- Original = Message -----
=0A
From: =0A Christopher =0A = Chapman
=0A
To: psnlist@..............
=0A
Subject: Re: Geophone Damping Mass Slew =0A= rate
=0A

=0A
=0A
=0A
=0A
=0A
=0A
=0A
=0A =0A
=0A
=0A
I =0A have been playing around with a d= ismantled SPZ geophone damping and find if you short =0A the leads to the coil and then drop the mass
the =0A mass will descend sl= owly, I guess from meeting the generator current =0A being dissipated by the internal =0A = resistance.

Questions arise from =0A this.
&nb= sp;
1. if there were no internal resistance =0A (superconductor) &= nbsp; then when the leads are shorted the mass would =0A fall
&nb= sp; a bit then stay forever hovering =0A ?

    Correct
=0A

=0A
2.the = =0A geophone is acting just like a rotating electrical ge= nerator
armature developing =0A to= rque under electrical loads ?

&nb= sp; Correct
=0A

=0A
3. =0A It seems to me = that seismic noise rarely hits the resonant =0A fr= equency and
you might do better to = not =0A increase the damping over what already
is =0A there in the mechanical and physical sense ?
=0A=
    No. The critical dam= ping allows you to get an =0A output voltage flat with frequency abov= e the resonant =0A frequency.

4. Does the rate a= t which the geophone =0A mass drop under heavy dam= ping represent some new fundamental Eigen frequency?
=0A

  &= nbsp; No. The resonance is determined by the mass of =0A the armature= and the spring constant.
=0A
&= nbsp;
=0A
5. =0A Can anyone provide me with = high school math models which represent the mechanical =0A and electrical<= /font> behaviors of the geophone?
H= igh school math being trig and =0A algebra minus the calculus?
=0A

=0A
    The theory is freely available on the =0A In= ternet.
=0A

=0A
an Eigen = freq not contained in EQ signals =0A then do no damping at a= ll?
This [little damping] should = =0A work for weak EQ signals and<= /font> not close =0A strong ones ?
=0A

=0A
    &nb= sp; An undamped geophone has a single =0A frequency peaked response - defi= nitely NOT what you want! =0A

&nb= sp;    Regards,
=0A

=0A
  &n= bsp; Chris =0A Chapman
<= /div>

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