PSN-L Email List Message

Subject: Re: HS-10-1 questions
From: "Geoff" gmvoeth@...........
Date: Fri, 30 Nov 2007 23:16:23 -0700

If your amplifier was designed for
a 24 Hz geophone it may not function right for a 1Hz
If you give your HS1 a gain of 1000 with a straight through
opamp into a 8 or 9 bit converter you should be able to
ping it with a 1mv to 100 uv across the leads and get a nice
sine wave if you use a diff amp with high input impedance.

I recommend you equalize it to 4seconds to 2 Hz or
possibly 1Hz to 2 Hz like the TUC station for
noisy background areas or wide open up to 10Hz
if you are in a quiet area.
I think you are not doing the opamp side of
things if not then you need the properly designed
amp from the pros.

I too have an HS10-1 at 1Hz and am getting a
acceptable picture for a total amature layman
this device is 400 Ohms very cold and about
440 Ohms in the summer.
That was b4 I put it underground maybe 24 inches.
24 inches deep being the base.

A diff amp you must match the components as closely
as possible for best CMMR ( Common mode rejection )
and any temp changes only affect the gain
and not the baseline if you zero it correctly.
Or so it seems to me.

Diff amp is where you hang the input
to the op amp +/- leads through
two matched resistors like 4700 ohms
if you want to damp more you put two matched
resistors to ground right at the geophone input.
For a 400 ohm unit 2K total damping seems to work OK.

The feedback resistors must also be matched and a
Two capacitors are needed across eack either
at about 10 Hz for a flat response DC to 10Hz
or at 4 seconds if you want things somewhat flat between
4 seconds and 2 Hz.

470K feedbacks seem to work well

Please be very careful with the
preamp design it will set the pace for
everything that follows.

I have only found two designs for the preamp that
worked for me using op177G op amps.
That were last MFG in the Philippines.

Just for fun:
I was waiting for a flight to catch
my ship in the tonkin gulf in 1972
when at the air terminal I was ripped off
by a Hari Krishna nut looking for
money for the Youth In Asia Movement
when I realized why these strange people
will sit in a lotus position and chant
the word "OOhhhmmm" If you had
1,000,000 people doing this you'd have
a mega"OOhhhmmm"s of resistance :-)
For 5 USD I got this strange book
that had a god with 6 arms or more
and since then at many times Id like
to have such a deformity.

Merry Hari Krishna, Hari Rama to everyone.


----- Original Message ----- 
From: "Andreas Tschammer" 
Sent: Friday, November 30, 2007 2:12 AM
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 
a German surplus dealer. I would like to do some experiments with active
damping/period extension (Lennartz-Method)
and  (pp. 50).

Today I found the time to do some tests to help me to decide whether 
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 
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. 
The resonance is also clearly visible. 
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 
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? 
Can you recommend any other test that can be done with normal electronic lab 
equipment to check the HS-10? 
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.. 

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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