## PSN-L Email List Message

Subject: Re: a possible seismometer?
From: ChrisAtUpw@.......
Date: Tue, 9 Dec 2008 01:00:08 EST

```
In a message dated 08/12/2008 21:50:51 GMT Standard Time,
PETERS_RD@.......... writes:

I've done an idealized calculation in which the water would be
replaced  with mineral oil and the plastic tube of the apparatus with a
thinwall  metal tube of length in the neighborhood of one  meter.

Hi Randall,

The problem with oil is that the viscosity  changes by x10 for every 20 C
Deg change in temperature. This is why oil  damping is 'difficult' /
virtually useless for seismometers.

You could use a glass U tube and mercury? Since  mercury is quite a good
electrical conductor, you could probably use magnetic  damping? But you would
have to thermostat the gas pressure chamber, which could  be tricky, otherwise
you are just making an expensive thermometer!

Another alternative would be to use a metal bellows  at the bottom end of
the tube, maybe with an additional spring, to provide the  pressure to
support a vertical liquid column.

Regards,

Chris Chapman

In a message dated 08/12/2008 21:50:51 GMT Standard Time,=20
PETERS_RD@.......... writes:
<=
FONT=20
style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2> =20
I've done an idealized calculation in which the water would bereplaced=
=20
with mineral oil and the plastic tube of the apparatus with athinwall=20
metal tube of length in the neighborhood of one=20
meter.

Hi Randall,

The problem with oil is that the viscosity=20
changes by x10 for every 20 C Deg change in temperature. This is why oi=
l=20
damping is 'difficult' / virtually useless for seismometers.

You could use a glass U tube and mercury? Since=
=20
mercury is quite a good electrical conductor, you could probably use magneti=
c=20
damping? But you would have to thermostat the gas pressure chamber, which co=
uld=20
be tricky, otherwise you are just making an expensive thermometer!

Another alternative would be to use a metal bel=
lows=20
at the bottom end of the tube, maybe with an additional spring, to provide t=
he=20
pressure to support a vertical liquid column.

Regards,

Chris Chapman
```