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
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