Hi John,

OK on the email.  In a "maintenance" sense, it would seem appropriate to
use the known test results, per each seismometer; to check on the pivot
wear sporadically.  I would think that if would be helpful.  I would guess
that
knife edge, razor edge pivots would show the most wear/friction, followed by
perhaps ball bearings....with my test hinge having its own particular
potential
problems, like lint/dirt getting in the rolling path etc.  Perhaps the best
would
be a true crossed rod pivot....but as far as a vertical seismo...I've yet to
"find" the
"common" material to be able to do that.

Meredith


On 11/1/07, John Lahr  wrote:
>
> Hi Meredith,
>
> There are two issues involved.  One is the absolute deflection due to
> adding a weight and the other is the electronic response, once some
> motion sensor has been applied.
>
> The absolute deflection when a weight is added is equivalent to
> changing the acceleration of gravity, which is also equivalent to
> applying a constant acceleration.  The deflection will be a function
> of the free period; the greater the period the greater the
> deflection.  This assumes that there is no friction at the hinge.  To
> test various hinges, one would want a very long period
> pendulum.  Then a very small weight should cause a known, specific
> deflection.  If there is less deflection, then the cause must be friction.
>
> Usually the term sensitivity relates to the electronic output per
> unit of motion, measured as displacement or velocity or acceleration
> at a given period.
>
> Cheers,
> John
>
>
>
Hi John,
 
OK on the email.  In a "maintenance" sense, it would seem appropriate to
use the known test results, per each seismometer; to check on the pivot
wear sporadically.  I would think that if would be helpful.  I would guess that
knife edge, razor edge pivots would show the most wear/friction, followed by
perhaps ball bearings....with my test hinge having its own particular potential
problems, like lint/dirt getting in the rolling path etc.  Perhaps the best would
be a true crossed rod pivot....but as far as a vertical seismo...I've yet to "find" the
"common" material to be able to do that.
 
Meredith
 
 
On 11/1/07, John Lahr <johnjan@........> wrote:
Hi Meredith,

There are two issues involved.  One is the absolute deflection due to
adding a weight and the other is the electronic response, once some

motion sensor has been applied.

The absolute deflection when a weight is added is equivalent to
changing the acceleration of gravity, which is also equivalent to
applying a constant acceleration.  The deflection will be a function

of the free period; the greater the period the greater the
deflection.  This assumes that there is no friction at the hinge.  To
test various hinges, one would want a very long period
pendulum.  Then a very small weight should cause a known, specific

deflection.  If there is less deflection, then the cause must be friction.

Usually the term sensitivity relates to the electronic output per
unit of motion, measured as displacement or velocity or acceleration

at a given period.

Cheers,
John