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
> __________________________________________________________
>
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 <
gmvoeth@...........> 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
__________________________________________________________