PSN-L Email List Message

Subject: Re: Instrumentation Question
From: "Dave Nelson" davefnelson@.......
Date: Sat, 29 Dec 2012 20:32:03 -0000


Hi Barry,

The latest  version of WinSdr (4.6.7) has the period extension =
capability which was intended for geophones and other non feedback =
sensors. It also has "derived Channels" which are additional output =
channels which  can use one of the standard input channels as a source =
but process the data differently.

The period extension is a new filter under the integrate / filter =
heading.   To set it up first download the new version and start it -- =
If you have an unused channel on the A/D just connect the seismometer to =
that channel in addition to the normal channel. If you need to add a new =
channel then go to the system settings/more options and select =
"additional channels" chose the number channels you wish to add.=20

Then --  go to settings and select the new channel and then select the =
source channel which will be one of the original 8.  Then select =
integrate /filter control  and enable the period  extension filter and =
set pendulum frequency to .02 Hz   (50 seconds for Inyo and Yuma)  leave =
Q at 0.707 the set High pass filter to .002 or .001 Hz and Q=3D 0.707.  =
Do NOT check the integrate data box.  Now  --- two options -- you can =
use the "post digital filter" or the normal event detection filter. If =
you use the post digital filter the data will be recorded as filtered =
and you have no options to change the filter on replay or transfer to =
WinQuake. If you use the normal  Event Detection filter the data will be =
recorded after the period extension process but before the second filter =
.. The settings in either case are .002 Hz 1 pole High Pass and I usually =
use .07 Hz low pass 6 pole. WinSdr will not accept a high pass at longer =
than 500 seconds (.002 Hz). I will ask Larry if it is possible to extend =
that filter to 1000 seconds.

When you start this channel it will take as much as an hour to settle =
and then the trace will be dominated by very long period noise . This is =
the actual seismometer self noise which is due to a lot of things such =
as 1/f noise , and dominated by pressure / temperature  rate effects. =
You will need to set the Y axis gain to 4 or more to  reduce the noise =
to an acceptable level.  If the instrument is not very well insulated =
from temperature change the very long period noise could be excessive =
but you  have seen earth normal modes before without a problem.

NOW --   we wait for a BIG event that generates the earth modes as  you =
have observed before.  The difference is the signal the normal  modes =
should be much larger as the long roll off of the instrument has =
de-convolved by the filter. I have yet to see an event so it is still =
unproven but the very long period noise I see is what I would expect.   =
I am using this technique on the Trillium Compact and my Napa sensors. I =
am waiting for delivery of a  new Nanometrics Trillium 120 which should =
have significantly reduced noise beyond 100 seconds. My own sensors were =
equal to or  better than the Trillium Compact so I need a better =
reference. =20

This capability will add a new dimension to our amateur seismic =
observations. THANKS  TO LARRY and BOB McCLURE !!!!

Cheers, Dave=20






 =20


From: Barry Lotz=20
Sent: Saturday, December 29, 2012 2:48 PM
To: psnlist@.................
Subject: Re: Instrumentation Question


Dave
The "real-time period extending filter in WinSdr". Is that the high =
pass/ low pass digital filter located with each channel or is there =
something else in the program that I'm not aware of ?=20

Regards
Barry
www.seismicvault.com







-------------------------------------------------------------------------=
-------
From: Dave Nelson 
To: psnlist@..............
Sent: Thu, December 27, 2012 3:33:06 PM
Subject: Re: Instrumentation Question


Hi Bob,

I have tried the real-time period extending filter in WinSdr with very =
good results . I am using it to extend the period of broadband force =
balance seismometers from 50 or 120 seconds to 1000 seconds   I know =
that was not the original intent but it really works well.  I have =
compared its performance with an analog "inverse filter" with =
essentially the same transfer function .The resulting waveforms are =
essentially identical. =20

I have not yet tried the WinQuake version but I will do so

My objective is to provide a system with real-time capability to observe =
earth normal modes following a large event and analyze the spectrum with =
WinQuake.  The increase in noise at  very long periods is clearly =
evident but that is expected and OK. The noise source  is mostly the =
instrument self noise enhanced by the period extension filter since the =
instrument noise is significantly above the low noise model beyond 100 =
seconds. The very long period waveforms from side by side broadband =
instruments are incoherent but they will be coherent  following a large =
teleseismic event upon excitation of the Normal modes. The period =
extension process could be either in the data acquisition as I am now =
doing , or in post processing using  WinQuake. The pros do it in post =
processing but they don't get so excited watching waveforms in real time =
like the amateurs.=20

Just one comment on the relative merits of the inverse  filtering =
techniques vs. the negative impedance loading for a geophone. When =
filtering a critically damped geophone the geophone dynamics are =
unchanged and the clipping level is unchanged. When the geophone is =
loaded with a negative impedance the dynamics of the seismic mass are =
changed dramatically. The mass is heavily over-damped and  moves much =
less in response to large ground displacements. One of the problems in =
seismic instrumentation for public safety is clipping. The over-damped =
geophone has a much larger dynamic range as well as period extension.

Thanks for the heads up on WinQuake and sorry for the overly long =
response. This is really interesting stuff and it gets me going :-}=20

Best Regards,

Dave =20










Hi Barry,
 
The latest  version of WinSdr = (4.6.7) has=20 the period extension capability which was intended for geophones and = other non=20 feedback sensors. It also has "derived Channels" which are additional = output=20 channels which  can use one of the standard input channels as a = source but=20 process the data differently.
 
The period extension is a new filter = under the=20 integrate / filter heading.   To set it up first download the = new=20 version and start it -- If you have an unused channel on the A/D just = connect=20 the seismometer to that channel in addition to the normal channel. = If you=20 need to add a new channel then go to the system settings/more options = and select=20 "additional channels" chose the number channels you wish to add. =
 
Then --  go to settings and = select the=20 new channel and then select the source channel which will be one of the = original=20 8.  Then select integrate /filter control  and enable the = period  extension filter and set pendulum frequency to .02 = Hz  =20 (50 seconds for Inyo and Yuma)  leave Q at 0.707 the set High = pass=20 filter to .002 or .001 Hz and Q=3D 0.707.  Do NOT check the = integrate=20 data box.  Now  --- two options -- you can use the "post = digital=20 filter" or the normal event detection filter. If you use the post = digital=20 filter the data will be recorded as filtered and you have no = options to=20 change the filter on replay or transfer to WinQuake. If you use the = normal=20  Event Detection filter the data will be recorded after the period=20 extension process but before the second filter . The settings in either = case are=20 ..002 Hz 1 pole High Pass and I usually use .07 Hz low pass 6 pole. = WinSdr will=20 not accept a high pass at longer than 500 seconds (.002 Hz). I will ask = Larry if=20 it is possible to extend that filter to 1000 seconds.
 
When you start this channel it will = take as much as=20 an hour to settle and then the trace will be dominated by very long = period noise=20 .. This is the actual seismometer self noise which is due to a lot = of things=20 such as 1/f noise , and dominated by pressure / temperature  rate = effects.=20 You will need to set the Y axis gain to 4 or more to  reduce the = noise to=20 an acceptable level.  If the instrument is not very well insulated = from=20 temperature change the very long period noise could be excessive = but you=20  have seen earth normal modes before without a = problem.
 
NOW --   we wait for a BIG = event that=20 generates the earth modes as  you have observed = before.  The=20 difference is the signal the normal  modes should be much = larger as=20 the long roll off of the instrument has de-convolved by the=20 filter. I have yet to see an = event so it is=20 still unproven but the very long period noise I see is what I would=20 expect.   I am using this technique on the Trillium Compact = and my=20 Napa sensors. I am waiting for delivery of a  new = Nanometrics Trillium=20 120 which should have significantly reduced noise beyond 100 seconds. My = own=20 sensors were equal to or  better than the Trillium Compact so I = need a=20 better reference.  
 
This capability will add a new = dimension to our=20 amateur seismic observations. THANKS  TO LARRY and BOB McCLURE=20 !!!!
 
Cheers, Dave
 
 
 
 
 
 
 

From: Barry Lotz
Sent: Saturday, December 29, 2012 2:48 PM
To: psnlist@..............
Subject: Re: Instrumentation Question

Dave
The=20 "real-time period extending filter in = WinSdr". Is that the high pass/ low pass digital filter located = with each=20 channel or is there something else in the program that = I'm not aware of ?=20
 
Regards
Barry
www.seismicvault.com




From: Dave Nelson <davefnelson@.......>
To: psnlist@..............
<= SPAN=20 style=3D"FONT-WEIGHT: bold">Sent: Thu, December 27, 2012 = 3:33:06=20 PM
Subject: Re: = Instrumentation=20 Question

Hi Bob,
 
I have tried the real-time period = extending=20 filter in WinSdr with very good results . I am using it to extend = the=20 period of broadband force balance seismometers from 50 or 120 seconds to = 1000=20 seconds   I know that was not the original intent but it = really works=20 well.  I have compared its performance with an analog "inverse = filter" with=20 essentially the same transfer function .The resulting waveforms are = essentially=20 identical. 
 
I have not yet tried the WinQuake = version but I will do so
 
My objective is to provide a = system with=20 real-time capability to observe earth normal modes following a large = event and=20 analyze the spectrum with WinQuake.  The increase in noise at  = very=20 long periods is clearly evident but that is expected and OK. The noise = source=20  is mostly the instrument self noise enhanced by the period = extension=20 filter since the instrument noise is significantly above the low noise = model=20 beyond 100 seconds. The very long period waveforms from side by side = broadband=20 instruments are incoherent but they will be coherent =  following a=20 large teleseismic event upon excitation of the Normal modes. The period=20 extension process could be either in the data acquisition as I am now = doing , or=20 in post processing using  WinQuake. The pros do it in post = processing=20 but they don't get so excited watching waveforms in real time like the=20 amateurs. 
 
Just one comment on the relative merits = of the=20 inverse  filtering techniques vs. the negative impedance loading = for a=20 geophone. When filtering a critically damped geophone the geophone = dynamics are=20 unchanged and the clipping level is unchanged. When the geophone is = loaded with=20 a negative impedance the dynamics of the seismic mass are changed = dramatically.=20 The mass is heavily over-damped and  moves much less in response to = large=20 ground displacements. One of the problems in seismic instrumentation for = public=20 safety is clipping. The over-damped geophone has a much larger = dynamic=20 range as well as period extension.
 
Thanks for the heads up on WinQuake and = sorry for=20 the overly long response. This is really interesting stuff and it gets = me going=20 :-}
 
Best Regards,
 
Dave  
 
 


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