PSN-L Email List Message

Subject: Re: Torsion Seismometer in a jar
From: =?ISO-8859-1?Q?J=F3n_Fr=EDmann?= jonfr@.........
Date: Fri, 16 Oct 2009 04:04:54 +0000


Is is possible to edit this design so it doesn't use glass jar and other
weak material ?

J=F3n Fr=EDmann.

On fim, 2009-10-15 at 16:27 -0400, kevin.mckee@....... wrote:
> Hi -
> I just joined this e-mail list, and noticed some of the discussion about =
the seismometer project I posted at
> There seemed to be some concern that the system would perform poorly or b=
e very noisy. There was some discussion over the LED being a cause for nois=
e. I performed a number of tests before I completed the seismometer (severa=
l years ago now) to satisfy my own concerns in that regard. I used various =
incandescent bulbs, LEDs and sensors, and in some cases, locked the pendulu=
m in a stationary position to test whether the sensor was picking up noise =
from the LED. In fact, I got a flat line even when the amplifier was maxed =
out--the LED was significantly quieter than other light sources.=20
> I've actually found the two devices that I've built (facing orthogonally)=
 to be very sensitive.  I've put together a rough distance-magnitude thresh=
old detection plot that I can forward to anyone who is interested. The weak=
est quake I've detected is a magnitude 2.0, about 0.05 degrees (about 3 mil=
es) away.  The common phases are easily picked out of the signal, depending=
 on the quake origin.=20
> The larger factor in the devices' sensitivity is that I mounted them on a=
 basement slab under the stairs to my front porch, which means that  they d=
etects the comings and goings of my family too (I sometimes used this fact =
to check up on my daughters' returns from dates).
> I believe that I am detecting microseismic background with the instrument=
 too, rather than air currents.=20
> Regarding the fact that the sensor is a displacement sensor vice a veloci=
ty sensor--I don't see that as a problem. As with a capacitive /radio frequ=
ency force-balance sensor, electronic filters and amplifiers can be used to=
 translate the signal into a velocity response, if that is what is desired.=
 In fact using the appropriate filter amplifier combination gets around any=
 concerns like those expressed about the resolution of the optical sensing =
devices--electronic integration works very well for that.
> Kevin McKee, Burke, VA
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