PSN-L Email List Message

Subject: My sticking Lehman?
From: tchannel1@............
Date: Fri, 30 May 2008 12:07:27 -0600


Hi Chris, and Others,   My problems with my new Lehman, have been =
resolved, I think......

I had one obvious problem:   At 20 seconds the arm would drift, left or =
right and I would need to reset it every two days.  The legs were =
threaded into the base, but loose, a lot of free play.  Knowing this I =
added a standard nut to lock the leg, which I would only finger tighten, =
this had always worked in the past.

What was happening is that the leg was moving itself.   Chris pointed =
out using two different materials would cause this.  But on other units =
it was never an issue.
In this case I removed the hex nut and added a wing nut.  After adj. I =
finger tighten the wing nut, nice and tight, and it has not drifted =
since.

The second problem:  At 20 seconds, I was missing all but large =
earthquakes, those were coming through just fine.   Chris suggest the =
arm might be sticking.  I could see nothing which resembled sticking.

I don't know if this was the cause and effect, but I fixed it:

First this is not the best Lehman I have ever built.  Its okay, and with =
little effort I got the 20 seconds, but I am not sure I could get 22.  =
However at 20 something was sticking. =20
I think at 20 it was so near infinity, it was almost flat.   At infinity =
it would never move to center, the arm would just stay where you placed =
it.  At 20 seconds it would move to center, if the event was large =
enough to overcome the inertia, but smaller earthquakes would not do =
this.=20

I reduce the period to 15 seconds, and it is working great.  I record =
6.2M Iceland, and 4.1M California.   I could, now increase the period to =
16,17,18 etc and retest.   I will see how it performs at 15 for a while.

Just wanted to share.








Hi Chris, and Others,   My = problems with=20 my new Lehman, have been resolved, I think......
 
I had one obvious problem:   = At 20=20 seconds the arm would drift, left or right and I would need to reset it = every=20 two days.  The legs were threaded into the base, but loose, a lot = of free=20 play.  Knowing this I added a standard nut to lock the leg, which I = would=20 only finger tighten, this had always worked in the past.
 
What was happening is that the leg was = moving=20 itself.   Chris pointed out using two different materials = would cause=20 this.  But on other units it was never an issue.
In this case I removed the hex nut and = added a wing=20 nut.  After adj. I finger tighten the wing nut, nice and tight, and = it has=20 not drifted since.
 
The second problem:  At 20 = seconds, I was=20 missing all but large earthquakes, those were coming through just=20 fine.   Chris suggest the arm might be sticking.  I could = see=20 nothing which resembled sticking.
 
I don't know if this was the cause and = effect, but=20 I fixed it:
 
First this is not the best Lehman I = have ever=20 built.  Its okay, and with little effort I got the 20 seconds, but = I am not=20 sure I could get 22.  However at 20 something was sticking. =20
I think at 20 it was so near infinity, = it was=20 almost flat.   At infinity it would never move to center, = the arm=20 would just stay where you placed it.  At 20 seconds it would move = to=20 center, if the event was large enough to overcome the inertia, but = smaller=20 earthquakes would not do this.
 
I reduce the period to 15 seconds, and = it is=20 working great.  I record 6.2M Iceland, and 4.1M = California.   I=20 could, now increase the period to 16,17,18 etc and retest.   I = will=20 see how it performs at 15 for a while.
 
Just wanted to share.
 
Thanks for the help. =20 Ted

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