PSN-L Email List Message

Subject: Re: Geophone Damping Mass Slew rate
From: Ed Ianni edwianni1@...........
Date: Thu, 16 Dec 2010 22:08:02 +0000


Hi Pete;

Concerning your damping advice, I have my "screen" in a different room 
from my seismograph, therefore I can't see it as I perform your 
procedure. Would there be a _VISIBLE_ dampening of the oscillations as 
the coil travels  through the magnetic field_at the seismograph._   
Thanks, Ed.


On 12/16/2010 8:59 PM, Pete Rowe wrote:
>
> Hi Ted
> With no damping, if you slightly push the arm off center and let go of 
> it you will see on the Winsdr trace on the screen oscillate back and 
> forth across zero for quite some time. With a 1 k pot across the coil, 
> adjust the pot  such that the oscillation goes across center and back 
> to the center with a tiny amount of overshoot. I can send you a 
> picture of this if it doesn't make sense.
> The pot value is correct for just slightly underdamped. You can 
> measure the pot and replace it with a fixed resistor.
>
> I will get back to you tomorrow with answers to the questions in your 
> e mail about parts  availability.
>
> Pete
> --- 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, 12:46 PM
>
>     Thanks again Pete...............If I have a coil which measures
>     1.2K ohms,  and another at 2.4K ohms.............what approx.
>     value should I try?     Should I use a Pot and adjust until I get
>     the effect I need and then measure the resistor value?
>     Ted
>
>         ----- Original Message -----
>         *From:* Pete Rowe 
>         *To:* psnlist@..............
>         
>         *Sent:* Thursday, December 16, 2010 1:18 PM
>         *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
>
>             This is kind of the same subject..................I
>             understand you can dampen a coil with a resistor,
>             Does anyone use this method in place of a Lehman style
>             magnet plate? I have for 20 years and
>             Do you give up anything (voltage) by using a resistor on
>             the coil?My coil measures about 10 k ohms and I use about
>             1 k for critical damping. I don't lose any sensitivity
>             If it works, why do we still use magnet plates to damp? It
>             works so well, I don't know why it isn't more popular.
>             Pete Rowe
>             Thanks, Ted
>
>                 ----- Original Message -----
>                 *From:* Christopher Chapman
>                 *To:* psnlist@..............
>                 *Sent:* Thursday, December 16, 2010 10:00 AM
>                 *Subject:* Re: Geophone Damping Mass Slew rate
>
>                 I have been playing around with a dismantled SPZ
>                 geophone damping and find if you short the leads to
>                 the coil and then drop the mass
>                 the mass will descend slowly, I guess from meeting the
>                 generator current being dissipated by the internal
>                 resistance.
>
>                 Questions arise from this.
>
>                 1. if there were no internal resistance
>                 (superconductor)   then when the leads are shorted the
>                 mass would fall
>                   a bit then stay forever hovering ?
>
>                     Correct
>                 2.the geophone is acting just like a rotating
>                 electrical generator
>                 armature developing torque under electrical loads ?
>
>                     Correct
>                 3. It seems to me that seismic noise rarely hits the
>                 resonant frequency and
>                 you might do better to not increase the damping over
>                 what already
>                 is there in the mechanical and physical sense ?
>                     No. The critical damping allows you to get an
>                 output voltage flat with frequency above the resonant
>                 frequency.
>
>                 4. Does the rate at which the geophone mass drop under
>                 heavy damping represent some new fundamental Eigen
>                 frequency?
>
>                     No. The resonance is determined by the mass of the
>                 armature and the spring constant.
>                 5. Can anyone provide me with high school math models
>                 which represent the mechanical and electrical
>                 behaviors of the geophone?
>                   High school math being trig and algebra minus the
>                 calculus?
>                     The theory is freely available on the Internet.
>                 an Eigen freq not contained in EQ signals then do no
>                 damping at all?
>                 This [little damping] should work for weak EQ signals
>                 and not close strong ones ?
>                       An undamped geophone has a single frequency
>                 peaked response - definitely NOT what you want!
>
>                     Regards,
>                      Chris Chapman
>
>
>



  
    
    
  
  
    Hi Pete;

Concerning your damping advice, I have my "screen" in a different room from my seismograph, therefore I can't see it as I perform your procedure. Would there be a VISIBLE dampening of the oscillations as the coil travels  through the magnetic field at the seismograph.   Thanks, Ed.


On 12/16/2010 8:59 PM, Pete Rowe wrote:

Hi Ted
With no damping, if you slightly push the arm off center and let go of it you will see on the Winsdr trace on the screen oscillate back and forth across zero for quite some time. With a 1 k pot across the coil, adjust the pot  such that the oscillation goes across center and back to the center with a tiny amount of overshoot. I can send you a picture of this if it doesn't make sense.
The pot value is correct for just slightly underdamped. You can measure the pot and replace it with a fixed resistor.

I will get back to you tomorrow with answers to the questions in your e mail about parts  availability.

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

From: Ted Channel <tchannel@............>
Subject: Re: Geophone Damping Mass Slew rate
To: psnlist@..............
Date: Thursday, December 16, 2010, 12:46 PM

Thanks again Pete...............If I have a coil which measures 1.2K ohms,  and another at 2.4K ohms.............what approx. value should I try?     Should I use a Pot and adjust until I get the effect I need and then measure the resistor value?
 
Ted
----- Original Message -----
From: Pete Rowe
Sent: Thursday, December 16, 2010 1:18 PM
Subject: Re: Geophone Damping Mass Slew rate



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

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

This is kind of the same subject..................I understand you can dampen a coil with a resistor, 
 
Does anyone use this method in place of a Lehman style magnet plate? I have for 20 years and
Do you give up anything (voltage) by using a resistor on the coil?My coil measures about 10 k ohms and I use about 1 k for critical damping. I don't lose any sensitivity
If it works, why do we still use magnet plates to damp? It works so well, I don't know why it isn't more popular.
Pete Rowe
 
Thanks, Ted
----- Original Message -----
Sent: Thursday, December 16, 2010 10:00 AM
Subject: Re: Geophone Damping Mass Slew rate

I have been playing around with a dismantled SPZ geophone damping and find if you short the leads to the coil and then drop the mass 
the mass will descend slowly, I guess from meeting the generator current being dissipated by the internal resistance. 
 
Questions arise from this. 
 
1. if there were no internal resistance (superconductor)   then when the leads are shorted the mass would fall 
  a bit then stay forever hovering ? 
 
    Correct
 
2.the geophone is acting just like a rotating electrical generator 
armature developing torque under electrical loads ? 
 
    Correct
 
3. It seems to me that seismic noise rarely hits the resonant frequency and 
  you might do better to not increase the damping over what already 
  is there in the mechanical and physical sense ?
 
    No. The critical damping allows you to get an output voltage flat with frequency above the resonant frequency. 
 
4. Does the rate at which the geophone mass drop under heavy damping represent some new fundamental Eigen frequency?

    No. The resonance is determined by the mass of the armature and the spring constant.  
 
5. Can anyone provide me with high school math models which represent the mechanical and electrical behaviors of the geophone
  High school math being trig and algebra minus the calculus?
 
    The theory is freely available on the Internet.
 
an Eigen freq not contained in EQ signals then do no damping at all? 
This [little damping] should work for weak EQ signals and not close strong ones ? 
 
      An undamped geophone has a single frequency peaked response - definitely NOT what you want! 

     Regards,
 
     Chris Chapman




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