Hello, Dont mean to butt in but It all seems too complex,

Velocity types are magnet coil arrangements.

the voltage relates to the strength and velocity of
the magnet/coil pair.

Maximum velocity/voltage happens as the movement crosses zero point.
Minimum velocity/voltage ( closest to zero ) happens at peak displacement(+/-)
I think velocity and voltage are a linear type equation.

When it comes to displacement only,
Maximum will be max or min capacitance which happens along with the motion.
I think capacitance is related to the square of the distance between the plates.
Thus is the voltage produced too.

While in motion These two types of sensors are producing signals
seperated , it seems to me ,  by 90 degrees at exactly the same moment in time.
One must be sin and the other cosin (your choice here) related to actual motion ??

It does make a difference which type of sensor you have.

But if you filter anything with hardware most likely you can never
be acactly sure what the picture is showing without being
able to compensate exactly with some kind of software
working over the data.

It seems moot to me that amateures are worrying about
things that cost big bucks to remedy and this kind of
thought belongs in the realm of the pros like USGS
or the OIL companies. 

I look at this with only the high school part of my math education.
I remember this better than college.

???

Any thoughts,

geoff



----- Original Message ----- 
From: "RSparks" 
To: 
Sent: Wednesday, November 25, 2009 10:37 AM
Subject: Re: Integrating in WinQuake CORRECTION


> Hello All,
> 
> Please withdraw my posting of Tue, 24 Nov 2009 23:04:04 -0800 (attached) 
> which contains a grievous error.  I incorrectly described the output of 
> the displacement and velocity detectors as being identical but as Chris 
> tried to tell me (following a previous reference to identity) (but I 
> failed to understand), they are much different. 
> 
> My error came when I wrote "
> 
> Knowing all the above, now let us make two seismometers, one using a 
> magnet/coil detector and one using a capacitive detector.  Move both 
> from position 1 to position 2.  Both will record a positive peak and 
> then a negative peak (or the reverse).  Each peak will correspond to the 
> maximum acceleration, the first peak to maximum initial acceleration and 
> the second peak to maximum deceleration (measured as negative 
> acceleration). 
> 
> Apparently we can use either displacement or velocity detection to 
> measure acceleration.
> 
> "
> The output of the displacement detector is correctly described but the 
> description of the output of the velocity sensor is grossly wrong.  
> During the movement from position 1 to position 2, the seismometer must 
> accelerate, reach a velocity, and then decelerate, stopping at position 
> 2.  Because the velocity detector is extracting energy from motion 
> through a magnetic field, the velocity detector first measures the 
> motion of the initial movement, then the motion caused by the return to 
> a zero position forced by the return mechanism, then the motion caused 
> by deceleration, and (finally) the motion of the final return to zero 
> position caused by the return mechanism after the stop at position 2 
> occurs.  For the velocity detector, the simple movement of the 
> seismometer from position 2 to position 2 yields two positive peaks and 
> two negative peaks. 
> 
> I write this before I have received any feedback.  I expect that several 
> commentators will describe the differences between the two detector 
> outputs as they point out my error, and will do a much better job than I 
> did.  My apologies to all for the initial misdirection. 
> 
> Roger
> 
> 
> psn-l-digest-request@.............. wrote:
>> .------ ------ ------ ------ ------ ------ ------ ------ ------ ------.
>> | Message 1                                                           |
>> '------ ------ ------ ------ ------ ------ ------ ------ ------ ------'
>> Subject: Re: Integrating in WinQuake
>> From:    RSparks 
>> Date:    Tue, 24 Nov 2009 23:04:04 -0800
>>
>> Hello All,
>>
>> Brett makes a particularly good point when he comments that "You can not 
>> say that a ground motion is only a displacement, or a velocity, or an 
>> acceleration, it is always all three.". Geoffrey makes the same point 
>> when he offers the equations that relate the three metrics.
>>
>> I am not familiar with the MEMS accelerometers but Wikipedia has an 
>> informative article on Accelerometers 
>> .  It is interesting to see 
>> that capacitive detection (which is displacement sensing)  is a common 
>> way for these micro seismometers to sense acceleration.  Other methods 
>> of detection (that I am not familiar with) are also used.
>>
>> Perhaps our experience with the automobile colors our thinking.  With 
>> the car, first we accelerate, then we have velocity and finally, 
>> distance is traveled.  A very time sequenced pattern.
>>
>> If we examine this same series of events on a micro scale, we can only 
>> find velocity (which may be zero) or change in velocity (acceleration).  
>> There is nothing else.  Any non zero measurement will have a distance 
>> component and a time component (back to the three equations). 
>>
>> Perhaps we should think of detection in terms of energy.  If we have 
>> velocity, then the moving mass has kinetic energy.   The magnet/coil 
>> system extracts energy from the velocity (and slows/opposes the relative 
>> motion) with the result that power is sent to the amplifier.  On the 
>> other hand, a capacitive or optic system uses external power to sense 
>> position. 
>>
>> Knowing all the above, now let us make two seismometers, one using a 
>> magnet/coil detector and one using a capacitive detector.  Move both 
>> from position 1 to position 2.  Both will record a positive peak and 
>> then a negative peak (or the reverse).  Each peak will correspond to the 
>> maximum acceleration, the first peak to maximum initial acceleration and 
>> the second peak to maximum deceleration (measured as negative 
>> acceleration). 
>>
>> Apparently we can use either displacement or velocity detection to 
>> measure acceleration.
>>
>> Roger
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
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>>   
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