PSN-L Email List Message

Subject: RE: Lehman sensor friction
From: "Gary Lindgren" gel@.................
Date: Sat, 18 Apr 2009 09:37:59 -0700

```Robert,
Looking at my Lehman notes, with polished tungsten carbide rods and with =
a
silicon carbide ball bearing I recorded going from 1.2" to .25" took 300
seconds. That calculates to 132 seconds for the half-life decay. I use =
the
equation Y=3DA*e-t/T where Y is the beam max. movement, A is a constant, =
t is
time in seconds, and T is the time constant of the system. I recall that
Chris Chapman said this was not quite the correct equation, but I'm sure =
it
is fairly close to describe the max. deviation with time.
Gary

-----Original Message-----
From: psn-l-request@.............. [mailto:psn-l-request@............... =
On
Behalf Of Robert O. Green
Sent: Saturday, April 18, 2009 8:27 AM
To: psn-l@..............
Subject: Lehman sensor friction

Gary,

I am curious.

What are typical times for Lehman half-life decay?

What are the main causes  of decay?

Rob

Gary Lindgren wrote:
> Jon,
> Without damping give the boom a light touch, what is the natural =
period.
> Count how many seconds it takes to make one cycle. Then count how long =
it
> takes for the displacement to go from one centimeter to 1/2 =
centimeter.
This
> will tell you how much friction you have in your sensor.
> Gary
>
>
>
>
> -----Original Message-----
> From: psn-l-request@.............. =
[mailto:psn-l-request@...............
On
> Behalf Of J=F3n Fr=EDmann
> Sent: Wednesday, April 15, 2009 4:26 PM
> To: psn-l@..............
> Subject: RE: Changes to my Lehman sensor
>
> Hi
>
> There is a peak around 0.6Hz, it might be the sensor it self that =
peaks
> like that. But it might also be natrual forces in my area that create
> this peak. I am not sure yet what natrual frequancy of the sensor is.
>
> Regards.
> J=F3n Fr=EDmann.
>
> On mi=F0, 2009-04-15 at 15:53 -0700, Gary Lindgren wrote:
>  =20
>> Jon,
>> What is the period length of your Lehman sensor. Were you able to =
measure
>> how long it takes for the boom displacement to drop by 1/2 after =
giving
it
>>    =20
> a
>  =20
>> light touch and this would be without damping in place.
>> Gary
>>
>>
>>
>>
>> -----Original Message-----
>> From: psn-l-request@.............. =
[mailto:psn-l-request@...............
>>    =20
> On
>  =20
>> Behalf Of J=F3n Fr=EDmann
>> Sent: Wednesday, April 15, 2009 11:20 AM
>> To: psn-l@..............
>> Subject: RE: Changes to my Lehman sensor
>>
>> Hi
>>
>> Here are pictures of the latest changes to my lehman sensor. One of =
the
>> change is that the top now has a hindge to make it more movable. In
>> theory that should provide me with better frequancy. However. I
>> continune to get the peak at 0.6Hz, even with thoise changes. The =
damper
>> plate is now aluminum, not steel.
>>
>> I am not sure how well this works until I get a earthquake close to
>> Iceland or some where in the world.
>>
>> Pictures.
>>
>> http://www.jonfr.com/myndir/v/geology/seismometer/p4150001b.jpg.html
>>
>> Regards.
>>    =20
>
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>  =20

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