PSN-L Email List Message
Subject: Re: My sticking Lehman?
From: tchannel1@............
Date: Fri, 30 May 2008 17:07:26 -0600
Thanks, Chris,
----- Original Message -----=20
From: ChrisAtUpw@..........
To: psn-l@.................
Sent: Friday, May 30, 2008 4:53 PM
Subject: Re: My sticking Lehman?
In a message dated 2008/05/30, tchannel1@............ writes:
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.
Hi Ted,
1) what top bearing / flexure are you using? (The top hinge =
is a SS wire, don't know the dia. but very thin.)
2) what bottom bearing / flexure are you using? (The bottom =
is a ball bearing on sidebyside drill bit shanks.)(this I think could be =
my weakest point, this arrangement may not be good enough) (I may =
rework this)
3) have you checked both the coil and the damping magnets for =
whiskers? They tend to grow with time and can cause the beam to stick. I =
use one of the pen lasers to check that the gaps are clear. Not sure =
what whiskers are............but it is a new machine.
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.
This is typical of a problem with the suspension system. I =
don't know what you expected to 'see', but you have just given a good =
description of what is observed. I suspect that you will not have fixed =
the problem by shortening the period, just reduced it a bit. The =
stiction, from whatever cause, will still be there.
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.
Regards,
Thanks, Chris,
----- Original Message -----
Sent: Friday, May 30, 2008 4:53 =
PM
Subject: Re: My sticking =
Lehman?
In a=20
message dated 2008/05/30, tchannel1@............=20
writes:
The second problem: At 20 seconds, I was missing =
all but=20
large earthquakes, those were coming through just fine. Chris =
suggest the=20
arm might be sticking. I could see nothing which resembled=20
sticking.
Hi=20
Ted,
1) what top bearing / =
flexure=20
are you using? (The top hinge is a SS wire, don't =
know the=20
dia. but very =
thin.)
2)=20
what bottom bearing / flexure are you using? (The bottom =
is a ball=20
bearing on sidebyside drill bit shanks.)(this I think could be my =
weakest=20
point, this arrangement may not be good enough) (I may rework=20
this)
3) have you checked both =
the=20
coil and the damping magnets for whiskers? They tend to grow with time =
and can=20
cause the beam to stick. I use one of the pen lasers to check that the =
gaps=20
are clear. Not sure what whiskers are............but it is =
a new=20
machine.
I don't know if this was the cause and effect, but I =
fixed=20
it:
First this is not the best Lehman I have ever =
built. =20
Its okay, and with little effort I got the 20 seconds, but I am not =
sure I=20
could get 22. However at 20 something was sticking. =
I think at 20 it =
was so near=20
infinity, it was almost flat. At infinity it would never move to =
center, the=20
arm 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.
This is=20
typical of a problem with the suspension system. I don't know what you =
expected to 'see', but you have just given a good description of what =
is=20
observed. I suspect that you will not have fixed the problem by =
shortening the=20
period, just reduced it a bit. The stiction, from whatever cause, will =
still=20
be there.
I reduce the period to 15 seconds, and it is working=20
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=20
will see how it performs at 15 for a while.
=20
Regards,
Chris =
Chapman=20
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