PSN-L Email List Message

Subject: Re: Integrating in WinQuake
From: "Geoffrey" gmvoeth@...........
Date: Wed, 9 Dec 2009 14:54:32 -0700

I am NO expert yet do have some experience with this seismic stuff,

It is not necessary to worry so much what is doing the sensing so long
as you see a nice signal coming in that gives a classic EQ signature.

The only better thing to do is to do exactly the same thing for all three
axises simultaneously then you can get a single magnitude
to look at as a vectored sum.

But you need three different A/D converters all working in synchronous
step collecting each sample ( all three) at the very same time.

Then you may use math to sort out the final display.

In absecence of this ability I simply settle for a Magnet/Coil
Vertical SPZ which is by far the simplest for an Amature.

Writing your own programs can be fun.

What is fine for a teenager here seems fine for me.
Even tho Im no teenager.

Thanks if anyone listened at all :-)

geoff [GVA]

----- Original Message ----- 
From: "RSparks" 
Sent: Wednesday, December 09, 2009 11:26 AM
Subject: RE: Integrating in WinQuake

> Hello Randall,
> Thanks for the informative posting relating sensors for seismometers.
> Here is an example that might complement the discussion.
> We all seem to agree that a coil/magnet sensor measures velocity and the displacement sensor measures location, both relative to 
> boom and case.  What I would like to add is that neither measurement completely defines conditions at the instant of measurement. 
> The measurement of velocity ignores location, and measurement of location ignores the component of velocity.  What we should do is 
> to measure BOTH components (two sensors on each boom) at the same instant.  Of course this would result in two data streams which 
> would not be identical.  For any one sine wave, maximum displacement would be measured when the velocity measurement was zero, 
> and maximum velocity at a zero displacement measurement.
> If we want to relate the two measurements, we can easily see that the distance traveled between any two DISPLACEMENT measurements 
> is the difference between the two measurements.  This difference is also velocity when considered as distance per sample (which is 
> distance per unit time).  This can also be considered as the differential of the data.
> On the other hand, if we want to convert our  VELOCITY readings to distance, we would need to find the average velocity between 
> each of two measured velocities which would be the sum of the two velocities divided by two, also considered as the integral of 
> the data.  We can not expect to simply integrate the velocity data and obtain distance because we would be using the velocities 
> measured at the distance points, not the average velocity that actually caused the resulting measured  traveled distance.
> Now assume that we want to calculate acceleration from the DISPLACEMENT DATA.  We would first calculate velocity by taking the 
> difference between the two readings.  Then we would take the difference between two of the velocity readings (a second 
> differential of displacement) to find the velocity change per time per time.  We would need at least three data points to make 
> this series of calculations.
> To find acceleration from the VELOCITY data, we can not simply find the difference between two velocity readings (which is the 
> velocity change per time per time (the first differential) ) because we would be using the velocities measured at distance points. 
> Instead, we should find the average velocity between two points and then find the difference between that average velocity and a 
> previous average velocity to reach an average acceleration.  Again, three data points would be required.
> We should notice that both of these processes to find acceleration are frequency sensitive and will suppress higher frequency data 
> fluctuation's.
> Finally, let us consider the STS device with a degenerative feedback system installed.  Our two sensors would register nearly zero 
> output because the feedback system works to minimize both velocity and travel of the boom.  As a result, energy as found in the 
> kinetic energy of velocity or energy in a spring is not allowed to be stored.  The reduced storage energy can be expected to 
> minimize the carry-over of energy from one data sample to another, thus reducing  distortion of the true wave form of the seismic 
> disturbance.  When a displacement sensor is used to generate the feedback signal, the resultant trace should still be a 
> displacement location.  When a velocity sensor is used to generate the feedback signal, the resultant trace should still be a 
> velocity trace but the output should about 1.4 times higher than the externally damped velocity output  because (nearly) all of 
> the incoming energy is available to generate a detectable reading (rather than being stored in the boom as kinetic energy or in 
> the spring as potential energy).
> Unfortunately, I do not have an STS device so I can not test this explanation.  Perhaps you or others can enlighten us about the 
> correctness or failure of this conjecture.
> Food for thought,
> Roger
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