Hi Dave,

 The latest version of WinQuake incorporates my period extending filter.
Download WinQuake 3.2.6 from
http://www.seismicnet.com/software.html#WinQuake. The filter can easily
provide a 10X improvement in bandwidth. I suggest you at least try it out.

Bob

On Thu, Dec 27, 2012 at 12:34 PM, Dave Nelson  wrote:

> **
> Hi Chris ,
>
> Yes I agree. I have been working extensively on period extension circuits
> for 4.5Hz geophones extending the period to 0.5 Hz.
>
> The so called Lippman circuit is just a well known negative impedance
> converter circuit  ( NIC) applied to geophones.  With the original
> Lippman circuit the output of the NIC is proportional to acceleration and
> subsequent circuits shape the spectrum to give the desired velocity
> response with the 2 slope roll off below the long period corner.  I have
> taken it a step further and modified the NIC to provide a velocity response
> at the output of the NIC. The result  is that there is no point in the
> active signal path where the signal is proportional  to acceleration.  The
> advantage is a significant improvement in clipping margin for a strong
> local event and better DC stability.
>
> Brett has created  a spice model which has been very helpful in optimizing
> the selection of the negative impedance load on the geophone. I am
> confident the same circuit could be used to extend the period of a 1 second
> geophone to ~ 20 seconds. I was able to use the circuit equally well
> for 4.5 Hz geophones  with both 380  and 4000 ohm coils. For the 1 second
> geophone a high resistance coil would be necessary to avoid impractical
> component values.
>
>  The DC gain of the NIC will become very high ( potentially unstable)  if
> you attempt to match the coil resistance with a negative resistance
> resulting in a near zero net resistance.  There is an optimum
> negative resistance  which provides good DC stability and the desired
> frequency response.
>
> The major disadvantage of all period extension methods is long period
> noise . A look at the Lennartz noise curves illustrates that very well. It
> is a unavoidable consequence of the technique ,however, for some
> applications like volcano monitoring it may not be important.  Low nose op
> amps are essential as you point out  The force feedback technique is
> dramatically lower noise so is the preferred method for periods longer than
> a few seconds.
>
>   I have been doing this work for a friend for a commercial application
> but the circuits are available. We can put them on Brett's website since I
> do not have a website.
>
> I am writing a PSN posting on my period extension experience -- just need
> to find the time.
>
> Regards,
>
> Dave Nelson
> Rolling Hills Estates, California
>
> I add my location to avoid confusion with my namesake from "downunder"
>
>
>
>
>
>  *From:* chrisatupw@.......
> *Sent:* Thursday, December 27, 2012 2:57 PM
> *To:* psnlist@..............
> *Subject:* Re: Instrumentation Question
>
>    From: Dave Nelson 
> To: psnlist 
> Sent: Mon, 24 Dec 2012 18:23
> Subject: Re: Instrumentation Question
>
> DC drift is very common --almost universal -- in seismometers. Even the
> best broadband instruments have a drift proportional to the rate of
> temperature change. The frequency content of the drift are usually well
> below the seismic information so is of no consequence.
>
> A 24 hour periodic drift is of absolutely no consequence for a geophone. For
> a 1 second instrument, even with period extension, the longest practical
> seismic signal which can be observed is probably around 20 seconds. The
> noise level at 20 seconds, after period extension, will be so high that only
> very large events will be observable above the instrument/system noise. A
> high pass filter in Winsdr at .05 Hz 1 pole or AC coupling with a time
> constant of about 3 seconds (20 seconds / 2pi) would be about right.
>
> Cheers,
> Dave Nelson
> Rolling Hills Estates, Hi Dave,****The noise that you see from a period extension circuit depends on the opamps used and on the
> circuit chosen.
> Period Extensions of up to x10 can be achieved using the Roberts' Circuit. The internal gain is x100.
> For Period Extensions of up to x50, you need the Lippmann circuit and a VERY low noise amplifier.
> The output short circuit current is very low.
> As far as I remember, Geoff is trying to use a Lippmann type circuit, so he should get reasonably low
>
> noise signals at 20 seconds.
> ****Brett Nordgren wrote ;Even professional instruments show substantial DC drift. Broadband
> verticals have an output proportional to the rate of temperature
> change and over a 24-hour period can easily vary by a volt or more
> depending on their thermal insulation. We routinely put in a
> one-pole digital high-pass filter at the lowest frequency available
> (0.002 Hz in WinSDR) which makes all that go away.
>
> ****An offset of over a volt could exceed the input range of some ADCs !!
> Such poor quality electronics would be totally unacceptable in my opinion.
>  >> Subject: Instrumentation Question
> >>
> >> Yet I can not rid a small DC drift which is either related to
> >> ambient AC noise level or DC drift of resistance or
> >> thermocouple voltage related to the soldering of junctions.
> >> This DC drift is related to the 24 hour cycle.
> >> The dc drift is on the order of micro volts
> >> which seem to be originating on the input.
> >> The overall DC gain is 80Dbv or X10000.
> >> I should be able to achieve a DC free drift at this gain.
> >> I am using a op177G op amp ??
> >> The sensor is HS10-1 Geophone.
> >> The 40 foot of cable is designed for burial
> >> it has silicon grease (I think) impregnated and
> >> has a heavy copper jacket.
> >> It is soldered at the geophone and also at the sensor
> >> has soldered connections.
> >
> >      If you use a CAZ type opamp like the LTC1150 you will get zero
> > temperature drift.
> >
> > The problem does not seem to be the amplifier itself.
> > But rather, the variables dealing with the input.
> > Cable/Geophone/Common mode stuff/
> > Yet I have found a wide variation within the
> > op amp offset voltages.
> > I am currently using a Chopper amp (or so I think)
> > In the front end. LTC1050 ???
> > Yes, I have troubles finding decent opamps
> > at civilian prices, the best are all seem to be MilSpec
> > rip offs. Outrageous prices. The milspec parts are by far
> > the best and all others should simply be scrapped.
> >
> > Regards,
> > geoff
> > LTC1050 - Precision Zero-Drift Operational Amplifier with Internal
> > Capacitors
>
> ***So is the LTC1150 ! Check it out ? !
>
>
> Regards,
>
>
> Chris Chapman
>
>
>
>
>
Hi Dave,=C2=A0<=
div>
<=
div>=C2=A0The latest version =
of WinQuake incorporates my period extending filter. Download=C2=A0<=
/font>from=C2=A0

http://www.seismicnet.com/softwar=
e.html#WinQuake. The filter can easily provide a 10X improvement in ban=
dwidth. I suggest you at least try it out.


=
Bob
On Thu, Dec 27, 2012 at 12:34 PM, Dave Nelson <=
span dir=3D"ltr"><davefnelson@.......> wrote:







Hi Chris ,
=C2=A0
Yes I agree. I have been working extensively on=
=20
period extension circuits for 4.5Hz geophones extending the period to 0.5 H=
z.=20

=C2=A0
The so called Lippman circuit is just a well know=
n=20
negative impedance converter circuit=C2=A0 ( NIC) applied to geophones.=20
=C2=A0With the original Lippman circuit the=20
output of the NIC is proportional to acceleration and subsequent circuits s=
hape=20
the spectrum to give the desired velocity response with the 2 slope roll=20
off=C2=A0below the=C2=A0long period corner. =C2=A0I have taken it a step further and modified the NIC to provide a=20
velocity response at the output of the NIC. The=C2=A0result =C2=A0is that t=
here=20
is no point in the active signal path where the signal is proportional=C2=
=A0 to=20
acceleration.=C2=A0 The advantage is a significant improvement in clipping=
=20
margin for a strong local event and better DC stability.=C2=A0 
=C2=A0
Brett has=C2=A0created=C2=A0=C2=A0a spice model=
=20
which has been very helpful in optimizing the selection of the negative=20
impedance load on the geophone. I am confident the same circuit could be us=
ed to=20
extend the period of a 1 second geophone to ~ 20 seconds. I was able to use=
 the=20
circuit equally well for=C2=A04.5 Hz geophones =C2=A0with both 380=C2=A0 an=
d=20
4000 ohm coils. For the 1 second geophone a high resistance coil would=20
be=C2=A0necessary to avoid impractical component values.
=C2=A0
=C2=A0The DC gain of the NIC will become very hig=
h=20
( potentially unstable)=C2=A0 if you attempt to match the coil resistance w=
ith a=20
negative resistance resulting in a near zero=C2=A0net resistance.=C2=A0 The=
re is=20
an optimum negative=C2=A0resistance=C2=A0 which provides good DC stability =
and=20
the desired frequency response.
=C2=A0
The major disadvantage of all period extension=20
methods is long period noise . A look at the Lennartz noise curves illustra=
tes=20
that very well. It is a unavoidable consequence of the technique ,however, =
for=20
some applications like volcano monitoring it may not be important.=C2=A0 Lo=
w=20
nose op amps are essential as you point out=C2=A0 The force feedback techni=
que=20
is dramatically lower noise so is the preferred method for periods longer t=
han a=20
few seconds.
=C2=A0
=C2=A0 I have been doing this work for a friend f=
or=20
a commercial application but the circuits are=
=20
available. We can put=C2=A0them on Brett's website since I do not have =
a=20
website.=C2=A0
=C2=A0
I am writing a PSN posting on my period extension=
=20
experience -- just need to find the time. 
=C2=A0
Regards, 
=C2=A0
Dave Nelson
Rolling Hills Estates, California 
=C2=A0
I add my location to avoid confusion with my=20
namesake from "downunder"=C2=A0
=C2=A0
=C2=A0
=C2=A0
=C2=A0




From: chrisatupw@....... 
Sent: Thursday, December 27, 2012 2:57 PM
To: psnlist@.............. 
Subject: Re: Instrumentation Question







From: Dave Nelson <davefnelson@.......>

To: psnlist <psnlist@..............>
Sent:=20
Mon, 24 Dec 2012 18:23
Subject: Re: Instrumentation=20
Question



<=
font color=3D"black" face=3D"arial">DC drift is very common --almost un=
iversal -- in seismometers. Even the=20
best broadband instruments have a drift proportional to the rate of=20
temperature change. The frequency content of the drift are usually well=20
below the seismic information so is of no consequence.

A 24 hour periodic drift is of absolutely no consequence for a geophone. Fo=
r=20
a 1 second instrument, even with period extension, the longest practical=20
seismic signal which can be observed is probably around 20 seconds. The=20
noise level at 20 seconds, after period extension, will be so high that onl=
y=20
very large events will be observab=
le above the instrument/system noise. A=20
high pass filter in Winsdr at .05 Hz 1 pole or AC coupling with a time=20
constant of about 3 seconds (20 seconds / 2pi) would be about right.

Cheers,
Dave Nelson
Rolling Hills Estates,=20

Hi Dave,
****The noise that you see=
 from a period extension circuit depends on the opamps used and on th=
e 

circuit chosen.

Period Extensions of up to x10 can be achieved using the =
Roberts' Circuit. The internal gain is x100. 

For Period Extensions of up to x50, you need the Lippmann circuit and=
 a VERY low noise amplifier. 

The output short circuit current is very low.   =


As far as I remember, Geoff is =
trying to use a Lippmann type circuit, so he should get reasonably low 

noise signals at 20 seconds. 

****Brett Nordgre=
n wrote ;
Even professional instruments show substantial DC drift. Broad=
band=20
verticals have an output proportional to the rate of temperature=20
change and over a 24-hour period can easily vary by a volt or more=20
depending on their thermal insulation. We routinely put in a=20
one-pole digital high-pass filter at the lowest frequency available=20
(0.002 Hz in WinSDR) which makes all that go away.


****An offset of over=
 a volt could exceed the input range of some ADCs !! 

Such poor quality electronics would be tota=
lly unacceptable in my opinion. 


=C2=A0>> Subject: Instrumentation Question
>>
>> Yet I can not rid a small DC drift which is either related to
>> ambient AC noise level or DC drift of resistance or
>> thermocouple voltage related to the soldering of junctions.
>> This DC drift is related to the 24 hour cycle.
>> The dc drift is on the order of micro volts
>> which seem to be originating on the input.
>> The overall DC gain is 80Dbv or X10000.
>> I should be able to achieve a DC free drift at this gain.
>> I am using a op177G op amp ??
>> The sensor is HS10-1 Geophone.
>> The 40 foot of cable is designed for burial
>> it has silicon grease (I think) impregnated and
>> has a heavy copper jacket.
>> It is soldered at the geophone and also at the sensor
>> has soldered connections.
>
>      If you use a CAZ type opamp like the LTC1150 you will get zero=20
> temperature drift.
>
> The problem does not seem to be the amplifier itself.
> But rather, the variables dealing with the input.
> Cable/Geophone/Common mode stuff/
> Yet I have found a wide variation within the
> op amp offset voltages.
> I am currently using a Chopper amp (or so I think)
> In the front end. LTC1050 ???
> Yes, I have troubles finding decent opamps
> at civilian prices, the best are all seem to be MilSpec
> rip offs. Outrageous prices. The milspec parts are by far
> the best and all others should simply be scrapped.
>
> Regards,
> geoff
> LTC1050 - Precision Zero-Drift Operational Amplifier with Internal=20
> Capacitors



***So is the LTC1150 ! Check it out ?=
 ! 



Regards, 


Chris Chapman





=