Hello tchannel;

If you were to mathematically combine
using trig or whatever three seismic signals
the signals must be captured in synchronization.
This means all samples (X,Y,Z) have to be collected
at the very same instants in time.
I have never seen such a thing before in
the civilian world.

geoff

----- Original Message ----- 
From: "tchannel" 
To: 
Sent: Friday, April 03, 2009 6:42 PM
Subject: Re: Designing a new vertical sensor


> Thanks, Geoffrey,   I will read your suggestions and notes carefully.
> 
> Ted
> 
> 
> ----- Original Message ----- 
> From: "Geoffrey" 
> To: 
> Sent: Friday, April 03, 2009 6:49 PM
> Subject: Re: Designing a new vertical sensor
> 
> 
>> NOTES From A layman (Vs Expert):
>> 
>> I believe that increasing the mass
>> will increase the signal to noise ratio but not sure.
>> I used an old 500Lb. seismometer once that
>> had a 100+ lb AVADUPOISE. ( I think ) mass and it would receive
>> even the surface waves well yet it was a 1 sec device.
>> Best vertical I ever tried.
>> USE Pb ( PlumBum ) as the mass.
>> A typical soda can of Lead.
>> Possibly 8 + LBS avd. or around 1 gallon of water.
>> 
>> I believe that using a balanced sensor will
>> make the electronics easier to build by
>> providing a proper input for a op amp diff amp.
>> As well as doubling the signal level
>> and somewhat lowering the noise level.
>> Noise will cancel 50% of the time but also
>> increase 50% time so possibly there is no
>> noise advantage to this.
>> 
>> A balanced sensor is two coils/magnets wired in
>> additive fashion with the center point grounded
>> making a single three wire sensor.
>> (SORT OF CLASS "B" push pull kind of thing but not exactly that)
>> But both must be matched as close as possible to being
>> identical. Both sensors can use the same mass
>> or be two separate single devices on the same
>> foundation (platform). Cable should be 100%
>> shielded and possibly the preamp located at the sensor
>> itself with maybe 50Ft of cable at most.
>> 
>> The shield should probably be cut just before reaching the
>> sensor but not sure. If everything is insulated from EARTH you
>> might surround even the sensor in the electrical ground.
>> Grounding is important to eliminate static and RFI
>> noise as well as the 60hz power hum that might originate
>> from power lines.
>> 
>> Use magnetic damping separate from the sensor
>> and you will get better output from the sensor.
>> 
>> IF you could place the mass in a vacuum
>> there would be no buoyancy effects for
>> changes in air density on the mass.
>> 
>> The greater the A/d Resolution the lower the overall
>> gain needs to be in the electronics.
>> 
>> Filter Low Pass the output so that the Aliasing
>> Freq occurs at 0Db or less of electrical gain if possible.
>> 
>> Match all your components as closely as possible
>> in the preamp to avoid baseline drifting and common
>> mode problems ( same signal on the two main signal leads ) .
>> 
>> Double regulate the power supply with at least
>> three+ volts between the output and the source.
>> So if you got 5 volts out you need at very least 8
>> volts in.
>> 
>> Anything at all that varies could affect the input
>> into your A/D converter. And all you want is pure signal.
>> 
>> The best of all would possibly be a three axis signal that is
>> mathematically combined to create a single magnitude.
>> But then you are not concerning yourself with the
>> three dimensions but only phases and first time
>> of arrival which is what interests myself the most.
>> 
>> Some people believe that the sensor magnet is fixed
>> to the physical ground
>> is the best way to go but not sure here since I have
>> had excellent results with short period devices
>> the other way around.
>> 
>> If you could string 100 devices together
>> 50 on each side of Signal ground
>> And locate them on the same platform
>> just think of the sensitivity
>> that might produce. But who has that
>> kind of monies
>> 
>> It seems to me that all kinds of waves
>> may be realized in the vertical since
>> when you squeeze or relax forces in the earth
>> bulges will be realized at the surface
>> as vertical motions.
>> ( Pardon my terms I am only a layman :-)  )
>> 
>> I think you are not interested in the electronics
>> but not sure about that. Need the tools.Expensive.
>> (designing/Making Your Own or building premade kits)
>> But you can do exactly what you want this way.
>> I do not recommend this unless you have great amount time
>> on your hands.
>> geoff
>> 
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