I am thinking possibly an optical feedback
system using a laser pointer or something
to feedback positional data to an electromagnet
you would use a PID loop of sorts like an auto
speed controller to fix the position of the
mass which is most likely a magnet hanging on
a spring as the mass itself.
You would get the signal somehow from the
PID loop as it keeps the mass stationary
like keeping an auto speed (MPH) steady.

Just A thought sort of like those
levitating globes but you would also
have a spring as well as larger mass
like 5 lb avdp or so instead of those lightweight globes.

Regards;
geoff


----- Original Message ----- 
From: "meredith lamb" 
To: 
Sent: Thursday, December 06, 2007 10:48 AM
Subject: Re: Combination spring-mag_levitation Anyone Tried This ??


> Hi Geoff,
> 
> No, "I" haven't heard of such....however right off I can't think of "how"
> one would do such
> especially with only one coil in a geophone.  Perhaps "if" you get away from
> a geophone
> and wander into say...a simple hanging spring with a mass on the bottom,
> then it might
> be more interesting (relatively unknown territory) as you might be able to
> add stuff, and go from there.
> My nephew David has used a hanging directional (horizontal) "S-G", with a
> natural period of ~ 1.5s
> and "added" acouple magnets; one to the bottom of the mass, and a much
> larger flat one below
> that.  The magnets are arranged to be repelling; i.e., with the same pole
> facing each other.
> If you carefully adjust the larger magnet it will extend the natural period
> of the S-G somewhat.
> David claimed he got up to a reliable 8 second natural period; but it
> involved precisely setting the
> positions of the magnets.  David claims he got up to 11 seconds; but that
> was alot less stable.
> He "settled" on using samarium magnets for his model, as the temperature
> results with
> neodymium magnets was less suitable.
> 
> I roughly tried it myself with the table top directional hanging horizontal
> model I have with
> the cross rod magnets pivot...about 10 days ago.  I only used a box on the
> floor to put the
> larger magnet on and position it directly underneath the small magnet on the
> bottom of the
> mass.....it was easy to get a extended 3 second period initially.  Visually
> it "appeared" that
> the undampened free oscillation swinging motion was reasonably harmonic.
> 
> I suppose there is likely a problem or problems with doing such...I've not
> really thought about
> it since the brief trial.  If one uses a coil and other magnets on
> such...then things get hairy
> with perhaps the potential of magnetic interaction potential
> problems...especially if the
> distances between the magnets is too close.
> 
> How the above could apply to your initial question; in regard to a hanging
> spring and mass
> or what results you might see are unknown.
> 
> I suppose one could also try such with about any vertical just to explore
> what happens?
> I would think the magnets "might" have to be, directly in front of the mass
> for a "traditional"
> vertical layout; rather than underneath....
> 
> I think Sprengnether company initially tried one or more magnetic
> seismometers way back
> in time.  But I know nothing of their results.
> 
> Good unknown questions, with no immediate answers....this is the kind of
> chewy stuff
> that makes for some fun trials....
> 
> Take care, Meredith
> On Dec 5, 2007 8:41 PM, Geoff  wrote:
> 
>> Hello PSN Folks;
>>
>> Has anyone ever used a spring
>> to take up most the mass weight then
>> maybe apply an ounce or less levitation
>> magnetically to set with electronics
>> the free period within a geophone.
>>
>> Id think you would pump a current limited signal
>> into the geophone and use some kind of
>> feedback circuit that might set
>> the free period. I am looking only
>> for a free period in the 3 to 4 second
>> range.
>>
>> If you take up the small weight with your hand
>> it seems you can move the hand up and down
>> at whatever period and the system will
>> not oppose what you are doing ??
>>
>> Comments welcome.
>>
>> Regards
>> geoff
>> __________________________________________________________
>>
>
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