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 -----
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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