## PSN-L Email List Message

Subject: Re: Building a lehman seismometer
From: "tchannel" tchannel@..............
Date: Thu, 5 Oct 2006 09:46:28 -0600

```Hi Chris,   A few questions:

1 Does your coil and damper assemblies just set on the aluminum base, =
free to move for adjustment, or are they fixed to the base?

2 You cleaned the plates, which hold the magnets, and then painted the =
exterior, but not the surface the magnets touch.  Would the paint =
interfere with something on that surface?

3 This is a hard question.  Assuming I have finished my sensor, and =
leveled it, what is the procedure for adjusting the period?  I know the =
target angle.
I would guess one would have to start at that point, with the base =
level, the pendulum level, and everything plumb.
You mentioned the formula for determining the angle of the hinge, I have =
that information.  Not knowing the correct procedure, and not being able =
to measure that small of an angle, I would have converted the angle into =
a decimal of inches, and measured the difference from the top hinge to =
the bottom hinge.  Maybe you could walk me through this procedure?

4 I get confused with many of these terms, so I hope you understand this =
question.  If the target period is say 10 seconds, would the arm move, =
when pulled 10mm, verrrrrrrrrry slowly, taking 10 seconds to complete =
one cycle?

5  After it is leveled and the period is set, Is it then that you can =
check the damp, by moving the arm 10mm and releasing it?
I know what an underdamped situation would look like.  But is there way =
to tell if it is over damped?

Thanks, Ted

----- Original Message -----=20
From: ChrisAtUpw@..........
To: psn-l@.................
Sent: Tuesday, October 03, 2006 9:23 PM
Subject: Re: Building a lehman seismometer

In a message dated 2006/10/04, jonfr500@......... writes:

I also plan to build a Lehman seismometer, if I can keep it small =
enough. But I need a suggestion for material and some mesurements and =
proper drawings before I can start. I also want to keep the frequency of =
the Lehman seismometer around 1Hz.

Hi Jon,=20

The  whole point about a Lehman type seismometer is that you =
take a pedulum which would have a period of about 1.3 to 1.5 sec if =
mounted vertically and extend the period to maybe 20 sec. The sensor =
will respond from 20 sec to the 10 Hz of your amplifier filter. I =
suspect that an arm of between 45 and 60 cm would be fine for you. Don't =
try to make it smaller. This should pick up your seismic signals very =
well.

I make a T / L frame with U channel Al with 5 mm Al plate for =
the corner supports. I don't know what materials are available to you. =
You can use 50 x 25 mm, but I prefer 75 x 25 mm section.

Regards,

Hi Chris,   A few =
questions:

1 Does your coil and damper =
assemblies just=20
set on the aluminum base, free to move for adjustment, or are they fixed =
to the=20
base?

2 You cleaned the plates, which =
hold the=20
magnets, and then painted the exterior, but not the surface the magnets=20
touch.  Would the paint interfere with something on that=20
surface?

3 This is a hard question.  =
Assuming I=20
have finished my sensor, and leveled it, what is the procedure for =
period?  I know the target angle.
I would guess one would have to start =
at that=20
point, with the base level, the pendulum level, and everything=20
plumb.
You mentioned the formula for =
determining the angle=20
of the hinge, I have that information.  Not knowing the correct =
procedure,=20
and not being able to measure that small of an angle, I would have =
converted the=20
angle into a decimal of inches, and measured the difference from the top =
hinge=20
to the bottom hinge.  Maybe you could walk me through this=20
procedure?

4 I =
get confused=20
with many of these terms, so I hope you understand this question.  =
If the=20
target period is say 10 seconds, would the arm move, when pulled 10mm,=20
verrrrrrrrrry slowly, taking 10 seconds to complete one =
cycle?

5  After it is leveled and the =
period is set,=20
Is it then that you can check the damp, by moving the arm 10mm and =
releasing=20
it?
I know what an underdamped situation =
would look=20
like.  But is there way to tell if it is over damped?

Thanks, Ted

----- Original Message -----
From:=20
ChrisAtUpw@.......
To: psn-l@..............
Sent: Tuesday, October 03, 2006 =
9:23=20
PM
Subject: Re: Building a lehman=20
seismometer
In a=20
message dated 2006/10/04, jonfr500@......... =
writes:
I also plan to build a Lehman seismometer, if I can keep =
it=20
small enough. But I need a suggestion for material and some =
mesurements and=20
proper drawings before I can start. I also want to keep the =
frequency of the=20
Lehman seismometer around 1Hz.Hi Jon,=20
The  whole point =
Lehman type seismometer is that you take a pedulum which would have a =
period=20
of about 1.3 to 1.5 sec if mounted vertically and extend the period to =
maybe=20
20 sec. The sensor will respond from 20 sec to the 10 Hz of your =
amplifier=20
filter. I suspect that an arm of between 45 and 60 cm would be fine =
for you.=20
Don't try to make it smaller. This should pick up your seismic signals =
very=20
well.       I make a T / L frame =
with U=20
channel Al with 5 mm Al plate for the corner supports. I don't know =
what=20
materials are available to you. You can use 50 x 25 mm, but I prefer =
75 x 25=20
mm section.      =20
Regards,       Chris Chapman=20

```