## PSN-L Email List Message

Subject: Re: Channel, 1,2 and 3?
From: "Jerry Payton" gpayton880@.......
Date: Sun, 23 Mar 2008 11:30:11 -0500

```Ahhhhh.  A new term (at least to me).  I get the usual dead-end by Googling
for "McComb-Romberg seismometer."  It always directs me to sites where you
have to be a member or pay for a copy.

Chris. do you know of a link showing this type of device?

Thanks,
Jerry

----- Original Message -----
From: ChrisAtUpw@.......
To: psn-l@..............
Sent: Sunday, March 23, 2008 11:20 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.
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.

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

Regards,

Chris Chapman

Ahhhhh.  A new term =
(at least to=20
me).  I get the usual dead-end by Googling for "McComb-Romberg=20
seismometer."  It always directs me to sites where you have to be a =
member=20
or pay for a copy.

Chris. do you know of a =
this type of device?

Thanks,
Jerry

----- Original Message -----
From: ChrisAtUpw@.......=20

To: psn-l@..............
Sent: Sunday, March 23, 2008 11:20 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 ground=20
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, with=20
a high moment of inertia but a small C of G to suspension distance, =
correct?=20
This type have a long period but a LOUSY =
sensitivity to=20
linear ground motion. They are however, sensitive to ground 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 Chapman
```