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) =
http://www.lennartz-electronic.de/
and  http://www.terrajp.co.jp/Seismometers.pdf  (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 =
the
terminals of the phone. The resonance was not very pronounced  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 has always a linear/sinusoidal output =
during this test.=20
The resonance is also clearly visible.=20
I am afraid the nonlinearity of 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) but 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 period adjustment=20
rod slowly up and down. I am not sure whether it comes from the =
astitisizing (typo?) spring or from the inside
of the housing.

Do you know whether this kind of non linear behaviour of the HS-10 is =
normal?=20
Can you recommend any other test that can be done with normal electronic =
lab=20
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








Hi all,
 
my name is Andreas Tschammer and I am =
from Germany.=20
I recently bought
a Geospace HS-10-1 vertical sensor (400 Ohms 3 =
V/ips) at=20
ebay from 
a German surplus dealer. I would like to do some =
experiments with=20
active
damping/period extension (Lennartz-Method) http://www.lennartz-electroni=
c.de/
and =20
http://www.terrajp.co.=
jp/Seismometers.pdf =20
(pp. 50).
 
Today I found the time to do some tests =
to help me=20
to decide whether 
to keep it or to send it back. It was =
not really a=20
bargain, so it should work 100%.
I was using a resistive bridge - as=20
described by ST Morrissey - to check
the resonance frequency and =
linearity. I=20
removed the 2k2 resistor from the
terminals of the phone. The =
resonance was=20
not very pronounced  between
1 Hz and 2 Hz. The sine current =
from the=20
function generator was about 30-100 uA
peak-peak. The up/down =
movement of the=20
period adjustment screw was very small but visible.
Especially below =
1 Hz the=20
output voltage of the coil was non sinusoidal. It looked as if 
the =
mass got=20
stuck by some kind of friction and then was released as the current was=20
growing.
I could make a picture of the =
oscilloskope screen=20
if this helps.
I have a 24 Hz geophone which has always a=20
linear/sinusoidal output during this test. 
The resonance is also clearly =
visible.=20

I am afraid the nonlinearity of =
the HS-10 will=20
be a problem when I try to LP filter the signal by software
to get rid of the high frequency =
seismic=20
noise.
The HS-10 seems to be pretty sensitive. =
I have it=20
sitting on the ground of the basement of my house
with a x100 amplifier and digital =
oscilloscope=20
connected. I can see movements all the time. It gets
lower at night (15 mVpp) but still =
a lot of=20
avtivity althought no cars can be heard outside. So its not totally=20
dead.
The coil resistance is ok. I can hear =
some kind of=20
klicking noise when I move the mass by the period adjustment =

rod slowly up and down. I am not sure =
whether it=20
comes from the astitisizing (typo?) spring or from the =
inside
of the housing.
 
Do you know whether this kind of non =
linear=20
behaviour of the HS-10 is normal? 
Can you recommend any other test =
that can=20
be done with normal electronic lab 
equipment to check the HS-10?=20

Is it possible/recommended to open the =
housing? I=20
was not able to find a way to open it.
Maybe I can see the problem inside.. =

 
I really would like to keep the HS-10, =
so any kind=20
of advise is welcome.
Thank you very much in advance for your =

help!
 


Andreas Tschammer
Rheinbach, Germany