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 =
adjustable=20
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 -----
Sent: Sunday, March 23, 2008 =
10:20=20
AM
Subject: Re: Channel, 1,2 and =
3?
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
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