PSN-L Email List Message

Subject: Re: Geophone Damping Mass Slew rate
From: Pete Rowe ptrowe@.........
Date: Thu, 16 Dec 2010 12:59:09 -0800 (PST)



Hi Ted
With no damping, if you slightly push the arm off center and let go of it y=
ou will see on the Winsdr trace on the screen oscillate back and forth acro=
ss zero for quite some time. With a 1 k pot across the coil, adjust the pot=
=A0 such that the oscillation goes across center and back to the center wit=
h 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 mai=
l about parts=A0 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

=0A=0A =0AThanks again Pete...............If I have a coil =0Awhich measure=
s 1.2K ohms,=A0 and another at 2.4K ohms.............what =0Aapprox. value =
should I try?=A0=A0=A0=A0 Should I use a Pot and =0Aadjust until I get the =
effect I need and then measure the resistor =0Avalue?=0A=A0=0ATed=0A=0A  --=
--- Original Message ----- =0A  From: =0A  Pete Rowe =0A  To: psnlist@webtr=
onics.com =0A  Sent: Thursday, December 16, 2010 1:18 =0A  PM=0A  Subject: =
Re: Geophone Damping Mass Slew =0A  rate=0A =20
=0A  =0A    =0A    =0A     =20

--- On Thu, 12/16/10, Ted Channel  =0A        wrote:
=0A       =20
From: =0A          Ted Channel 
Subject: =0A          Re: Geophone Damping Mass Slew rate
To: psnlist@..............
Date: =0A          Thursday, December 16, 2010, 12:11 PM

=0A          =0A          =0A=0A          This is kind of the same =0A     =
     subject..................I understand you can dampen a coil with a =0A=
          resistor,=A0 =0A          =A0=0A          Does anyone use this me=
thod in place of a =0A          Lehman style magnet plate? I have =0A      =
    for 20 years and
=0A          Do you give up anything (voltage) by =0A          using a resi=
stor on the coil?My =0A          coil measures about 10 k ohms and I use ab=
out 1 k for critical =0A          damping. I don't lose any sensitivity
=0A          If it works, why do we still use magnet =0A          plates to=
 damp? It works so well, =0A          I don't know why it isn't more popula=
r.
Pete =0A          Rowe
=0A          =A0=0A          Thanks, Ted=0A          =0A            ----- O=
riginal Message ----- =0A            From: =0A            Christopher Chapm=
an =0A            To: psnlist@.............. =0A            =0A            =
Sent: Thursday, December 16, =0A            2010 10:00 AM=0A            Sub=
ject: Re: Geophone Damping =0A            Mass Slew rate=0A           =20
=0A            =0A            =0A            =0A            =0A            =
=0A            =0A            =0A            =0A            =0A            =
=0A            I =0A            have been playing around with a dismantled =
SPZ =0A            geophone damping and find=A0if you short the leads to th=
e coil and then drop the mass=A0
the mass will descend =0A            slowly, I guess from meeting=A0the gen=
erator current 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 when the leads are shorted the =0A            mass would fall=A0
=A0 a bit then stay forever hovering =0A            ?=A0
=A0
=A0=A0=A0 =0A            Correct=0A            =A0=0A            2.the =0A =
           geophone is acting just like a rotating electrical generator=A0
armature developing torque under electrical loads =0A            ?=A0
=A0
=A0=A0=A0 =0A            Correct=0A            =A0=0A            3. =0A    =
        It seems to me that seismic noise rarely hits the resonant frequenc=
y and=A0
=A0 you might do better to not increase the damping over =0A            wha=
t already=A0
=A0 is there in the =0A            mechanical and physical sense ?=0A      =
      =A0=0A            =A0=A0=A0 No. The critical damping allows you to =
=0A            get=A0an output voltage flat with frequency above the resona=
nt =0A            frequency.=A0
=A0
4. Does the rate at which the =0A            geophone mass drop under heavy=
 =0A            damping=A0represent some new fundamental =0A            Eig=
en frequency?=0A           =20
=A0=A0=A0=A0No. The resonance is determined by =0A            the mass of t=
he armature and the spring constant. =0A=A0=0A            =A0=0A           =
 5. =0A            Can anyone provide me with high school =0A            ma=
th=A0models which represent the mechanical and=A0electrical =0A            =
behaviors of the geophone?=A0
=A0 High =0A            school math being trig and algebra=A0minus the calc=
ulus?=0A            =A0=0A            =A0=A0=A0 The theory is freely availa=
ble on the =0A            Internet.=0A            =A0=0A            an Eige=
n freq not contained in EQ =0A            signals then do no damping =0A   =
         at all?=A0
This =0A            [little damping] should work for weak EQ signals =0A   =
         and not close strong ones ?=A0=0A            =A0=0A            =A0=
=A0=A0=A0=A0 An undamped geophone has =0A            a single frequency pea=
ked response - definitely NOT what you =0A            want!=A0 =0A         =
  =20
=A0=A0=A0=A0 Regards,=0A            =A0=0A            =A0=A0=A0=A0 Chris =
=0A            Chapman

Hi Ted
With no damping, if you slightl= y 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. Wi= th a 1 k pot across the coil, adjust the pot  such that the oscillatio= n 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 val= ue is correct for just slightly underdamped. You can measure the pot and re= place 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@.......... net> wrote:

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

=0A=0A =0A
Thanks again Pete...............If I have a coil =0Awhich measur= es 1.2K ohms,  and another at 2.4K ohms.............what =0Aapprox. va= lue should I try?     Should I use a Pot and =0Aadjust = until I get the effect I need and then measure the resistor =0Avalue?
=0A
 
=0A
<= font size=3D"2" face=3D"Arial">Ted
=0A
=0A
--= --- Original Message -----
=0A =0A =0A
Sent:= Thursday, December 16, 2010 1:18 =0A PM
=0A
Subject: Re: Geophone Damping Mass Slew =0A rate=0A

=0A =0A =0A =0A


--- On = Thu, 12/16/10, Ted Channel <tchannel@............> =0A wrote:
= =0A

From: =0A Ted Channel <= tchannel@............>
Subject: =0A Re: Geophone Damping Mass Slew rate
To: =
psnlist@.............. m
Date: =0A Thursday, December 16, 2010, 12:11 PM

= =0A
=0A