## PSN-L Email List Message

Subject: Re: Any Info on Time Constant for Undamped Vertical Sensor
From: ChrisAtUpw@.......
Date: Fri, 28 Nov 2008 21:55:03 EST

```=20
In a message dated 28/11/2008 23:42:02 GMT Standard Time, =20
gel@................. writes:

I=E2=80=99m just getting started with my first vertical  seismometer. I will=
be using=20
an extension spring and supported at 90 degrees.  Bearing concept is 2 sets=20
of tungsten carbide rods and a silicon carbide ball  bearings. One of the=20
springs I have tested is a Century Spring No. 312. K  factor is .28 pounds/i=
nch and=20
resonant period is 1.25 seconds. The tungsten  rods are as received and have=
=20
not been polished yet. Undamped, I measured the  damping constant to be 372=20
seconds. I used the equation of Y=3DA*e-t/T. How does  the 372 seconds compa=
re to=20
other vertical systems. =20

Hi Gary,
=20
If you can extend the top spring position beyond  the vertical support=20
and also lower it a bit, you will get a longer period.  The aim is to have t=
he=20
vertical above the hinge nearer the ''zero'' length of  the spring.
=20
If you put a C shaped plate on the end of the  horizontal beam, you coul=
d=20
use two short piano wire supports in tension. I  have also used a pair of=20
n. I=20
stick them between Al cross strips with  acrylic adhesive with a gap of ~0.1=
".
=20
You should be able to improve on 1.25  seconds. Aim for a period of 1.5=20
to 2 seconds.=20
=20
Regards,
=20
Chris Chapman

In a message dated 28/11/2008 23:42:02 GMT Standard Time,=20
gel@................. writes:
<=
FONT=20
style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>
I=E2=80=99m just getting started with my first vertic=
al=20
seismometer. I will be using an extension spring and supported at 90 degre=
es.=20
Bearing concept is 2 sets of tungsten carbide rods and a silicon carbide b=
all=20
bearings. One of the springs I have tested is a Century Spring No. 312. K=20
factor is .28 pounds/inch and resonant period is 1.25 seconds. The tungste=
n=20
rods are as received and have not been polished yet. Undamped, I measured=20=
the=20
damping constant to be 372 seconds. I used the equation of Y=3DA*e-t/T. Ho=
w does=20
the 372 seconds compare to other vertical systems.=20

Hi Gary,

If you can extend the top spring position beyon=
d=20
the vertical support and also lower it a bit, you will get a longer per=
iod.=20
The aim is to have the vertical above the hinge nearer the ''zero'' length o=
f=20
the spring.

If you put a C shaped plate on the end of the=20
horizontal beam, you could use two short piano wire supports in tension=
.. I=20
have also used a pair of razor blades extracted from single blade cheap plas=
tic=20
razors in compression. I stick them between Al cross strips with=20
acrylic adhesive with a gap of ~0.1".

You should be able to improve on 1.25=20
seconds. Aim for a period of 1.5 to 2 seconds.

Regards,

Chris Chapman
```