PSN-L Email List Message

Subject: RE: HS-10-1 questions
From: "Jack Ivey" ivey@..........
Date: Fri, 30 Nov 2007 10:41:37 -0500

Are you inadvertently overdriving the seismometer so it is hitting the =
end stops?  Seems
unlikely that would happen with only 100uA through 400 ohms.  What =
happens when you reduce=20
your test current to 1/10 as much?

The clicking noise may be normal.  I have a Ranger 1-second seismometer, =
and when
you load and unload the spring the mass hits the end stops and makes a =
noise.  Is there a centering indicator on your unit?  On the ranger =
there is a window
with a pointer to let you get the mass centered.

Although I normally take the case off anything I buy first thing, but I =
would be careful=20
about disassembling an expensive seismometer apart without instructions =
from the manufacturer,=20
it might require assembly  tools and procedures you don't have to get it =
back together. =20
Maybe others have better information.

I would like to use the Lenmartz method with my Ranger, so I am =
interested in=20
your future progress.


From: psn-l-request@.............. [mailto:psn-l-request@............... =
On Behalf Of Andreas Tschammer
Sent: Friday, November 30, 2007 4:13 AM
To: PSN-L@..............
Subject: HS-10-1 questions

Hi all,
my name is Andreas Tschammer and I am from Germany. I recently bought
a Geospace HS-10-1 vertical sensor (400 Ohms 3 V/ips) at ebay from=20
a German surplus dealer. I would like to do some experiments with active
damping/period extension (Lennartz-Method) =
and=A0 (pp. 50).
Today I found the time to do some tests to help me to decide whether=20
to keep it or to send it back. It was not really a bargain, so it should =
work 100%.
I was using a resistive bridge - as described by ST Morrissey - to check
the resonance frequency and linearity. I removed the 2k2 resistor from =
terminals of the phone. The resonance was not very pronounced=A0 between
1 Hz and 2 Hz. The sine current from the function generator was about =
30-100 uA
peak-peak. The up/down movement of the period adjustment screw was very =
small but visible.
Especially below 1 Hz the output voltage of the coil was non sinusoidal. =
It looked as if=20
the mass got stuck by some kind of friction and then was released as the =
current was growing.
I could make a picture of the oscilloskope screen if this helps.
I have a 24 Hz geophone which=A0has always a linear/sinusoidal =
output=A0during this test.=20
The resonance=A0is also clearly visible.=20
I am afraid the nonlinearity=A0of the HS-10 will be a problem when I try =
to LP filter the signal by software
to get rid of the high frequency seismic noise.
The HS-10 seems to be pretty sensitive. I have it sitting on the ground =
of the basement of my house
with a x100 amplifier and digital oscilloscope connected. I can see =
movements all the time. It gets
lower at night (15 mVpp)=A0but still a lot of avtivity althought no cars =
can be heard outside. So its not totally dead.
The coil resistance is ok. I can hear some kind of klicking noise when I =
move the mass by the=A0period adjustment=20
rod slowly up and down. I am not sure whether it comes from the =
astitisizing (typo?)=A0spring or from the inside
of the housing.
Do you know whether this kind of non linear behaviour of the HS-10 is =
Can you recommend any other test that can be done with normal electronic =
equipment to check the HS-10?=20
Is it possible/recommended to open the housing? I was not able to find a =
way to open it.
Maybe I can see the problem inside..=20
I really would like to keep the HS-10, so any kind of advise is welcome.
Thank you very much in advance for your help!

Andreas Tschammer
Rheinbach, Germany

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