PSN-L Email List Message
Subject: Re: Adjusting the period
From: tchannel1@............
Date: Tue, 27 May 2008 17:15:57 -0600
Hi Chris, =20
>Is it solid Al, 2.5" OD? I meant to say 2.5 pounds, alum 3" x 3" =
cylinder.
Ted
----- Original Message -----=20
From: ChrisAtUpw@..........
To: psn-l@.................
Sent: Tuesday, May 27, 2008 2:40 PM
Subject: Re: Adjusting the period
In a message dated 2008/05/27, tchannel1@............ writes:
>Is the seismometer right next to an outside wall? (Yes)=20
>Which direction does the wall face? (East/West)
Hi Ted,
A location close to a load bearing outside wall is likely to be =
effected by any movements of the wall, due to rainfall on the soil =
outside, the effect of the sun raising the wall temperature and also =
noise from winds.=20
>What are the dimensions of the Lehman, what is the boom made of and =
what is the mass? 36" boom 1/2" alum rod. Dim. 20"wide, 22" tall, 36" =
long. The mass is 2.5# Alum cylinder
Thanks. What is the weight of the Aluminum cylinder, please - =
or alternatively it's length? Is it solid Al, 2.5" OD?
Chris, I think I found the drift issue? I added a wing nut to lock =
the legs after adjustment. I think they were moving over time?
That could well be the problem. Threads are cut at about a 60 =
degree angle and are rarely a tight fit. If the thread and the nut / =
threaded insert are not of the same material, you get differential =
expansion which slides the threads radially. Similarly, unless the =
adjusting screw is under tension, any differential expansion of the =
frame relative to the Earth underneath will try to tilt the thread and =
cause it to slip diagonally. It is preferable to use a wavy spring =
washer between the wing nut / lock nut and the frame to keep a fairly =
constant tension. This will not be much effected by the small amounts of =
differential expansion of the base and the bolt.=20
Let us know if this cures your drift problems?
Regards,
Hi Chris,
>Is it solid Al, 2.5" =
OD? I meant to=20
say 2.5 pounds, alum 3" x 3" cylinder.
Ted
----- Original Message -----
Sent: Tuesday, May 27, 2008 =
2:40 PM
Subject: Re: Adjusting the =
period
In a=20
message dated 2008/05/27, tchannel1@............=20
writes:
>Is the seismometer right next to an outside =
wall? =20
(Yes)
>Which direction does the wall face?=20
(East/West)
Hi=20
Ted,
A location close to a =
load=20
bearing outside wall is likely to be effected by any movements of the =
wall,=20
due to rainfall on the soil outside, the effect of the sun raising the =
wall=20
temperature and also noise from winds.
>What are the dimensions of the Lehman, what is the =
boom made=20
of and what is the mass? 36" boom 1/2" alum rod. Dim. =
20"wide,=20
22" tall, 36" long. The mass is 2.5# Alum cylinder
Thanks.=20
What is the weight of the Aluminum cylinder, please - or alternatively =
it's=20
length? Is it solid Al, 2.5" OD?
Chris, I think I found the drift issue? I added a =
wing nut=20
to lock the legs after adjustment. I think they were moving =
over=20
time?
=20
That could well be the problem. Threads are cut at about a 60 degree =
angle and=20
are rarely a tight fit. If the thread and the nut / threaded insert =
are not of=20
the same material, you get differential expansion which slides the =
threads=20
radially. Similarly, unless the adjusting screw is under tension, any=20
differential expansion of the frame relative to the Earth underneath =
will try=20
to tilt the thread and cause it to slip diagonally. It is preferable =
to use a=20
wavy spring washer between the wing nut / lock nut and the frame to =
keep a=20
fairly constant tension. This will not be much effected by the small =
amounts=20
of differential expansion of the base and the bolt.=20
Let us know if this cures =
your=20
drift problems?
=20
Regards,
Chris =
Chapman=20
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