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"To: 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 > > > > > > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with the body of the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. > __________________________________________________________ Public Seismic Network Mailing List (PSN-L)