I have been intrigued by the concept of using a liquid as the seismic =
mass in a broadband instrument for some time. The original thought came =
the idea that a damping plate was being moved through a liquid -- why =
not move the liquid through the damping plate. I  have also studied the =
MET seismometer ( I operate a CME MET vertical seismometer in my home =
system ) and have a moderate understanding of its principals and the =
electrochemistry involved.

To be brief I have been working for some months to develop a credible =
instrument with no moving parts. After a lot of internet searches on the =
related technologies and several learning experiences (read as total =
failure) I came up wit a concept based on well known principals but with =
some unique twists. The instrument uses water( with some off- the- shelf =
additives) in a simple structure that resembles a large electrolytic =
tiltmeter. The baseline of the first instrument was 1 meter. The key was =
to have  the fluid  flow  heavily overdamped to the point of creating  a =
hydraulic integrator . Damping is provided by a small conical seat =
valve.The equivalent orifice when the valve is set for operation is less =
than 1mm.  Electrolytic transducers in the usual bridge arrangement  are =
at each end of a horizontal water column. The electronics consist of a =
LTC1043 switched capacitor front end and two dual op amps -- that's ALL =
..The result is a very credible broadband seismometer (5 Hz to more than =
40 seconds -velocity).

Some key points on performance:

Noise from the electronics is negligible.

Seismic background noise dominates. The day / night variation is clearly =
visible

Two identical instruments side by side see exactly the same signal in =
absolute lock step.

Microseism is clearly visible and can on occasion be the dominant  =
background.

When filtered for short period the output exactly matches an HS-10-1 =
background signal  cycle by cycle.

Telesesmic body  and surface waves are recorded with  sensitivity  and =
fidelity  equal to my MET broadband and other broadband instruments =
reported on the PSN network and  other sources like the Berkeley =
Seismological Laboratory. In one case a seismometer within 100 miles =
matched nearly cycle by cycle for a teleseismic event.

In short my test results are still a bit qualitative but I am convinced =
(much to my surprise and pleasure) that the instrument is in family with =
some very good broadband seismometers.

This is a VERY simple device . Nothing moves but water.=20

The entire thing cost less than 50 bucks from the hardware store =
plumbing department and the local electronics store (except for the =
LTC1043). I have built four systems , Two 1 meter and Two 1/2 meter =
baseline.  Setup takes a little time to get the fluid level adjusted and =
the instrument leveled. A test point provides the level adjustment =
signal to a digital VM. Stabilization can take several hours, once =
stable no attention is required as long as the base is stable. No =
attempt has been made to create a  tiltmeter, the electronics are AC =
coupled with a 6.6 second (40 second period) time constant, slow / small =
 tilt drift  is not a problem.

I will be requesting permission to post events to PSN to back up what I =
have claimed. I will  also be writing a detailed description, with =
pictures, to be  available on request.=20

This is new stuff ,in operation about a month so development is still =
underway. I have also been looking a vertical based on the same basic =
concept,not sure about that yet but it looks possible.

On  a personal note, I am a  retired electrical engineer with extensive =
experience in instrument design , aerospace engineering and program =
management -- this is not quack stuff.

I believe I have something which could be of considerable interest to =
the seismology community and am anxious to share what I have learned. I =
prefer the telephone for detail discussion as I am not a good typist . I =
am from the old school where a secretary did the typing so I am  bit =
slow on the keyboard.
=20
I am looking forward to reading your comments and possibly telling me =
how I reinvented the wheel. (If so, I haven't found that wheel).

Dave Nelson

(The one from LA  --  not Australia)












I have been intrigued by the concept of =
using a=20
liquid as the seismic mass in a broadband instrument for some time. The =
original=20
thought came the idea that a damping plate was being moved through a =
liquid --=20
why not move the liquid through the damping plate. I  have also =
studied the=20
MET seismometer ( I operate a CME MET vertical seismometer in =
my home=20
system ) and have a moderate understanding of its principals and the=20
electrochemistry involved.
 
To be brief I have been working for =
some months to=20
develop a credible instrument with no moving parts. After a lot of =
internet=20
searches on the related technologies and several learning experiences =
(read as=20
total failure) I came up wit a concept based on well known principals =
but with=20
some unique twists. The instrument uses water( with some off- the- shelf =

additives) in a simple structure that resembles a large electrolytic =
tiltmeter.=20
The baseline of the first instrument was 1 meter. The key was to =
have  the=20
fluid  flow  heavily overdamped to the point of creating =
 a=20
hydraulic integrator . Damping is provided by a small conical =
seat=20
valve.The equivalent orifice when the valve is set for operation =
is less=20
than 1mm.  Electrolytic transducers in the usual bridge=20
arrangement  are at each end of a horizontal water column. The =
electronics=20
consist of a LTC1043 switched capacitor front end and two dual op =
amps --=20
that's ALL .The result is a very =
credible=20
broadband seismometer (5 Hz to more than 40 seconds =
-velocity).
 
Some key points on =
performance:
 
Noise from the electronics is=20
negligible.
 
Seismic background noise dominates. The =
day / night=20
variation is clearly visible
 
Two identical instruments side by side =
see exactly=20
the same signal in absolute lock step.
 
Microseism is clearly visible and can =
on occasion=20
be the dominant  background.
 
When filtered for short period the =
output exactly=20
matches an HS-10-1 background signal  cycle by cycle.
 
Telesesmic body  and surface waves =
are=20
recorded with  sensitivity  and fidelity  equal to my MET =

broadband and other broadband instruments reported on the PSN network =
and =20
other sources like the Berkeley Seismological Laboratory. In one =
case a=20
seismometer within 100 miles matched nearly cycle by cycle for a =
teleseismic=20
event.
 
In short my test results are still a =
bit=20
qualitative but I am convinced (much to my surprise and pleasure) that =
the=20
instrument is in family with some very good broadband =
seismometers.
 
This is a VERY simple device . Nothing =
moves but=20
water. 
 
The entire thing cost less than 50 =
bucks from=20
the hardware store plumbing department and the local electronics store =
(except=20
for the LTC1043). I have built four systems , Two 1 meter and Two 1/2 =
meter=20
baseline.  Setup takes a little time to get the fluid level =
adjusted and=20
the instrument leveled. A test point provides the level adjustment =
signal to a=20
digital VM. Stabilization can take several hours, once stable =
no=20
attention is required as long as the base is stable. No attempt has been =
made to=20
create a  tiltmeter, the electronics are AC coupled with a 6.6 =
second (40=20
second period) time constant, slow / small  tilt drift  =
is not a=20
problem.
 
I will be requesting permission to post =
events to=20
PSN to back up what I have claimed. I will  also be writing a=20
detailed description, with pictures, to be  available on =
request.=20

 
This is new stuff ,in operation about a =
month so=20
development is still underway. I have also been looking a vertical =
based on=20
the same basic concept,not sure about that yet but it looks=20
possible.
 
On  a personal note, I am a  =
retired=20
electrical engineer with extensive experience in instrument design , =
aerospace=20
engineering and program management -- this is not quack =
stuff.
 
I believe I have something which could =
be of=20
considerable interest to the seismology community and am anxious to =
share what I=20
have learned. I prefer the telephone for detail discussion as I am not a =
good=20
typist . I am from the old school where a secretary did the typing=20
so I am  bit slow on the keyboard.
 
I am looking forward to reading your =
comments and=20
possibly telling me how I reinvented the wheel. (If so, I haven't found =
that=20
wheel).
 
Dave Nelson
 
(The one from LA  --  not=20
Australia)