## PSN-L Email List Message

Subject: Re: Channel, 1,2 and 3?
From: tchannel1@............
Date: Thu, 27 Mar 2008 08:57:20 -0600

```Hi Chris and Everyone,  At this point in time, I do believe the "Nearly =
Balanced Pendulum" makes for a "LOUSY" Sensor.  Although it does pick up =
local noise really well.
I have samples of this Ch3 devise, set at 20 second period, events from =
the North, and the East, and the sensor recorded nothing,  I reset the =
period to 7 seconds and received the Honduras from the S/E and still =
nothing.  I am going to reset the period to 2 seconds and test it one =
last time,  then rebuild it into a Lehman.

Some of you have a good understanding of why this did not work.  Chris =
indicated (below) some of the reasons.
I think I understand.  However could someone explain why ch1 works okay, =
and ch3 does not work at all.

Ch1 is a 42" vertical pendulum, just hanging there like a clock =
pendulum, same coil, magnet and hinge as the sensor in question.
Ch3 'THE LOUSY SENSOR' is a 36" below the pivot pendulum and about 36" =
above the pivot, similar to an airplane propeller.  It has an adjustable =
mass which can go up or down the shaft above the pivot to extend the =
period......and this it does very well, as I can get very long periods =
up to 53 seconds. =20

I tend to learn many things from my failures, and this seems to be one =
of those opportunities.  I did post all three channels on PSN.  ch2 is a =
vertical.

Cheers, Ted
----- Original Message -----=20
From: ChrisAtUpw@..........
To: psn-l@.................
Sent: Sunday, March 23, 2008 10:20 AM
Subject: Re: Channel, 1,2 and 3?

In a message dated 23/03/2008, johnjan@........ writes:
My understanding of a long period physical pendulum is that =
sensitivity to ground motion is sacrificed in order to obtain the long =
period.=20
Hi Ted,

That is NOT my understanding in general.

But you are using a nearly balanced pendulum, with a high moment =
of inertia but a small C of G to suspension distance, correct? This type =
have a long period but a LOUSY sensitivity to linear ground motion. They =
are however, sensitive to ground rotation.=20

Longer period pendulums like the Lehman and the Romberg are very =
sensitive to linear ground motion and make good seismometers.

Regards,

Hi Chris and Everyone,  At this point in time, I do believe =
the=20
"Nearly Balanced Pendulum" makes for a "LOUSY" Sensor.  Although it =
does=20
pick up local noise really well.
I have samples of this Ch3 devise, set at 20 second period, events =
from the=20
North, and the East, and the sensor recorded nothing,  I reset the =
period=20
to 7 seconds and received the Honduras from the S/E and still =
nothing.  I=20
am going to reset the period to 2 seconds and test it one last =
time,=20
then rebuild it into a Lehman.

Some of you have a good understanding of why this did not =
work.  Chris=20
indicated (below) some of the reasons.
I think I understand.  However could someone explain why ch1 =
works=20
okay, and ch3 does not work at all.

Ch1 is a 42" vertical pendulum, just hanging there like a clock =
pendulum,=20
same coil, magnet and hinge as the sensor in question.
Ch3 'THE LOUSY SENSOR' is a 36" below the pivot pendulum and about =
36"=20
above the pivot, similar to an airplane propeller.  It has an =
mass which can go up or down the shaft above the pivot to extend the=20
period......and this it does very well, as I can get very long periods =
up to 53=20
seconds.

I tend to learn many things from my failures, and this seems to be =
one of=20
those opportunities.  I did post all three channels on PSN.  =
ch2 is a=20
vertical.

Cheers, Ted

----- Original Message -----
From:=20
ChrisAtUpw@.......
To: psn-l@..............
Sent: Sunday, March 23, 2008 =
10:20=20
AM
Subject: Re: Channel, 1,2 and =
3?

In a message dated 23/03/2008, johnjan@........ writes:
My=20
understanding of a long period physical pendulum is that sensitivity =
to=20
ground motion is sacrificed in order to obtain the long=20
period.

Hi Ted,

That is NOT my understanding in =
general.

But you are using a nearly balanced =
pendulum,=20
with a high moment of inertia but a small C of G to suspension =
distance,=20
correct? This type have a long period but a LOUSY=20
sensitivity to linear ground motion. They are however, sensitive to =
ground=20
rotation.

Longer period pendulums like the Lehman=20
and the Romberg are very sensitive to linear ground motion and =
make good=20
seismometers.

Regards,

Chris=20
Chapman
```