Kevin, I very much like your sensor in a jar.  Even the most excepted 
standards and designs at one time were unique.   I try everything I can 
think of, but must admit I never tried one in a jar.   I have used very long 
vertical spring which understandably would have great thermo expansion 
issues, but I have not seen any problem using them successfully.   I place 
my sensors in a living area, garage or basement and the temperature is more 
or less constant.   I ran a test in a 55 degree room, using a heater, warmed 
the room to 75 but could see no effect on the trace.  I know the 48" long 
vertical spring was expanding, but it did not change anything I could see. 
My normal room temp.  changes very little.

On the other hand I have seen massive noise with air currents.   I too keep 
these to a minimum.

Anyhow, well done on your jar, I want to build one if I can find the time.

This hobby, for me, is exciting because of the constant innovations.    The 
fact is, many of these ideas, will not work, some will, but not well, and 
some will work just fine.    Its always fun to see new approaches.

Thanks, for sharing,
Ted



----- Original Message ----- 
From: 
To: 
Cc: 
Sent: Friday, October 16, 2009 3:21 AM
Subject: Re: Digest from 10/15/2009 00:01:59


> Perhaps one or both of my postings weren't clear.
>
> The devices rest on a basement slab in a conditioned space. They are 
> enclosed by a thick Styrofoam box which significantly reduces air 
> currents. These two factors reduce the temperature variation of the 
> instruments, although I don't doubt there could be a couple of degrees 
> variation over the course of long periods relative to the period of the 
> damped pendulum/filter combinations. Because that temperature varies over 
> relatively long times, however, I judge that it is trivial after 
> considering that the ac-coupled integrator suppresses signals longer than 
> about 20 seconds.
>
> Also, the instruments use glass fibers for the torsion fiber and glass 
> jars for the structural supports in part to reduce the effects of thermal 
> contraction and expansion. Glass has a significantly lower thermal 
> expansion coefficient than any of the metal pendulums used for the Lehman 
> instruments of which I am aware, for example. Moreover, the dimension of 
> the expansion is orthogonal to the directional sensitivity of the 
> instrument; I hoped that this would further reduce sensitivity to thermal 
> variation.
>
> I recognize that this instrument is not a lab quality instrument, but for 
> something that can be built so cheaply and easily by anyone without a lot 
> of technical or machining skills it's a very useful device. I've detected 
> at least 120 earthquakes from all over the world with it.
>
> Why discourage folks out there who don't have the skills or $ to build a 
> Porsche when a Ford will get the job done, while spreading the fun of 
> doing science?
>
> Kevin McKee, burke, VA
>
> ---- psn-l-digest-request@.............. wrote:
>
> =============
>
> .------ ------ ------ ------ ------ ------ ------ ------ ------ ------.
> | Message 1                                                           |
> '------ ------ ------ ------ ------ ------ ------ ------ ------ ------'
> Subject: Torsion Seismometer in a jar
> From:    
> Date:    Thu, 15 Oct 2009 16:27:19 -0400
>
> Hi -
> I just joined this e-mail list, and noticed some of the discussion about 
> the seismometer project I posted at 
> http://tinkeringcaveman.googlepages.com/home
>
> There seemed to be some concern that the system would perform poorly or be 
> very noisy. There was some discussion over the LED being a cause for 
> noise. I performed a number of tests before I completed the seismometer 
> (several years ago now) to satisfy my own concerns in that regard. I used 
> various incandescent bulbs, LEDs and sensors, and in some cases, locked 
> the pendulum in a stationary position to test whether the sensor was 
> picking up noise from the LED. In fact, I got a flat line even when the 
> amplifier was maxed out--the LED was significantly quieter than other 
> light sources.
>
> I've actually found the two devices that I've built (facing orthogonally) 
> to be very sensitive.  I've put together a rough distance-magnitude 
> threshold detection plot that I can forward to anyone who is interested. 
> The weakest quake I've detected is a magnitude 2.0, about 0.05 degrees 
> (about 3 miles) away.  The common phases are easily picked out of the 
> signal, depending on the quake origin.
>
> The larger factor in the devices' sensitivity is that I mounted them on a 
> basement slab under the stairs to my front porch, which means that  they 
> detects the comings and goings of my family too (I sometimes used this 
> fact to check up on my daughters' returns from dates).
>
> I believe that I am detecting microseismic background with the instrument 
> too, rather than air currents.
>
> Regarding the fact that the sensor is a displacement sensor vice a 
> velocity sensor--I don't see that as a problem. As with a capacitive 
> /radio frequency force-balance sensor, electronic filters and amplifiers 
> can be used to translate the signal into a velocity response, if that is 
> what is desired. In fact using the appropriate filter amplifier 
> combination gets around any concerns like those expressed about the 
> resolution of the optical sensing devices--electronic integration works 
> very well for that.
>
>
> Kevin McKee, Burke, VA
>
>
> .------ ------ ------ ------ ------ ------ ------ ------ ------ ------.
> | Message 2                                                           |
> '------ ------ ------ ------ ------ ------ ------ ------ ------ ------'
> Subject: Re: Torsion Seismometer in a jar
> From:    ChrisAtUpw@.......
> Date:    Thu, 15 Oct 2009 18:13:04 EDT
>
>
> -------------------------------1255644784
> Content-Type: text/plain; charset="US-ASCII"
> Content-Transfer-Encoding: 7bit
>
>
> In a message dated 15/10/2009 21:27:46 GMT Daylight Time,
> kevin.mckee@....... writes:
>
> There  seemed to be some concern that the system would perform poorly or 
> be
> very  noisy. There was some discussion over the LED being a cause for
> noise. I used  various incandescent bulbs, LEDs and sensors, and in some 
> cases,
> locked the  pendulum in a stationary position to test whether the sensor 
> was
> picking up  noise from the LED. In fact, I got a flat line even when the
> amplifier was  maxed out--the LED was significantly quieter than other 
> light
> sources.
>
>
>
> Hi Kevin,
>
>    You seem to be experiencing apparatus problems.  Ordinary LEDs are much
> more noisy than superbright or IR LEDs. Both vary in  light output by 
> about
> x5 between 0 and 100 C. The is a HUGE variation. They are  both more noisy
> than a filament bulb driven from a regulated voltage source.  Your flat 
> line
> response was probably due to low gain. You should be able to pick  up
> microseisms all the time.
>    You can build a very good detector using two large  area Si photocells
> BPW34 connected to a differential amplifier. I get a noise  level of about
> 14 nano metres. You can't get adequate stability with a single  detector 
> or
> with a LED which is not temperature compensated. Phototransistors  are
> extremely noisy compared to photodiodes. You can get very fine Nichrome 
> wire
> which makes a good suspension. Alternatively, you can use a single glass 
> or
> carbon filament.
>
>    Regards,
>
>    Chris Chapman
>
>
>
> -------------------------------1255644784
> Content-Type: text/html; charset="US-ASCII"
> Content-Transfer-Encoding: quoted-printable
>
> 
> 
> 
> 
>  id=3Dr=
> ole_body=20
> bottomMargin=3D7 leftMargin=3D7 rightMargin=3D7 topMargin=3D7> id=3Dr=
> ole_document=20
> color=3D#000000 size=3D2 face=3DArial>
> 

> 
In a message dated 15/10/2009 21:27:46 GMT Daylight Time,=20
> kevin.mckee@....... writes:
>  style=3D"BORDER-LEFT: blue 2px solid; PADDING-LEFT: 5px; MARGIN-LEFT: 
> 5px"=
>>  style=3D"BACKGROUND-COLOR: transparent" color=3D#000000 size=3D2 face=3D=
> Arial>There=20
>  seemed to be some concern that the system would perform poorly or be ver=
> y=20
>  noisy. There was some discussion over the LED being a cause for noise.=
> I used=20
>  various incandescent bulbs, LEDs and sensors, and in some cases, locked=
> the=20
>  pendulum in a stationary position to test whether the sensor was picking=
> up=20
>  noise from the LED. In fact, I got a flat line even when the amplifier=
> was=20
>  maxed out--the LED was significantly quieter than other light sources.=
> =20
>  

> 

> 
Hi Kevin,
> 
 
> 
    You seem to be experiencing apparatus 
> problem=
> s.=20
> Ordinary LEDs are much more noisy than superbright or IR LEDs. Both vary=
> in=20
> light output by about x5 between 0 and 100 C. The is a HUGE variation. 
> The=
> y are=20
> both more noisy than a filament bulb driven from a regulated voltage 
> sourc=
> e.=20
> Your flat line response was probably due to low gain. You should be able=
> to pick=20
> up microseisms all the time.
> 
    You can build a very good detector using two=
> large=20
> area Si photocells BPW34 connected to a differential amplifier. I get a 
> no=
> ise=20
> level of about 14 nano metres. You can't get adequate stability with a 
> sin=
> gle=20
> detector or with a LED which is not temperature compensated. 
> Phototransist=
> ors=20
> are extremely noisy compared to photodiodes. You can get very fine 
> Nichrom=
> e wire=20
> which makes a good suspension. Alternatively, you can use a single 
> gl=
> ass or=20
> carbon filament. 
> 
 
> 
    Regards,
> 
 
> 
    Chris Chapman
> 
 
> 
    
>
> -------------------------------1255644784--
>
>
> .------ ------ ------ ------ ------ ------ ------ ------ ------ ------.
> | Message 3                                                           |
> '------ ------ ------ ------ ------ ------ ------ ------ ------ ------'
> Subject: Re: Torsion Seismometer in a jar
> From:    "tchannel" 
> Date:    Thu, 15 Oct 2009 17:18:47 -0600
>
> This is a multi-part message in MIME format.
>
> ------=_NextPart_000_000A_01CA4DBB.8E711840
> Content-Type: text/plain;
> charset="iso-8859-1"
> Content-Transfer-Encoding: quoted-printable
>
> Hi Chris,  the two large area Si photocells BPW34 connected to a =
> differential amplifier, sound like something I would like to try.  Could =
> you help me with a simple schematic of this, even a sketch?   Does the =
> amp just use easy to find op amps?
>
> Thanks, Ted
>  ----- Original Message -----=20
>  From: ChrisAtUpw@..........
>  To: psn-l@.................
>  Sent: Thursday, October 15, 2009 4:13 PM
>  Subject: Re: Torsion Seismometer in a jar
>
>
>  In a message dated 15/10/2009 21:27:46 GMT Daylight Time, =
> kevin.mckee@....... writes:
>    There seemed to be some concern that the system would perform poorly =
> or be very noisy. There was some discussion over the LED being a cause =
> for noise. I used various incandescent bulbs, LEDs and sensors, and in =
> some cases, locked the pendulum in a stationary position to test whether =
> the sensor was picking up noise from the LED. In fact, I got a flat line =
> even when the amplifier was maxed out--the LED was significantly quieter =
> than other light sources.=20
>
>  Hi Kevin,
>
>      You seem to be experiencing apparatus problems. Ordinary LEDs are =
> much more noisy than superbright or IR LEDs. Both vary in light output =
> by about x5 between 0 and 100 C. The is a HUGE variation. They are both =
> more noisy than a filament bulb driven from a regulated voltage source. =
> Your flat line response was probably due to low gain. You should be able =
> to pick up microseisms all the time.
>      You can build a very good detector using two large area Si =
> photocells BPW34 connected to a differential amplifier. I get a noise =
> level of about 14 nano metres. You can't get adequate stability with a =
> single detector or with a LED which is not temperature compensated. =
> Phototransistors are extremely noisy compared to photodiodes. You can =
> get very fine Nichrome wire which makes a good suspension. =
> Alternatively, you can use a single glass or carbon filament.=20
>
>      Regards,
>
>      Chris Chapman
>
>
> ------=_NextPart_000_000A_01CA4DBB.8E711840
> Content-Type: text/html;
> charset="iso-8859-1"
> Content-Transfer-Encoding: quoted-printable
>
> 
> 
>  http-equiv=3DContent-Type>
> 
> 
> 
>  id=3Drole_body=20
> bottomMargin=3D7 leftMargin=3D7 rightMargin=3D7 topMargin=3D7 =
> bgColor=3D#ffffff>
> 
Hi Chris,  the two large area Si photocells BPW34 connected to =
> a=20
> differential amplifier, sound like something I would like to try.  =
> Could=20
> you help me with a simple schematic of this, even a sketch?   =
> Does the=20
> amp just use easy to find op amps?
> 
 
> 
Thanks, Ted
>  style=3D"BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; =
> PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px"=20
> dir=3Dltr>
>  
----- Original Message ----- 
>    style=3D"FONT: 10pt arial; BACKGROUND: #e4e4e4; font-color: =
> black">From:=20
>    href=3D"mailto:ChrisAtUpw@.......">ChrisAtUpw@....... 
>  
To:  title=3Dpsn-l@.................
>  href=3D"mailto:psn-l@..............">psn-l@.............. 
>  
Sent: Thursday, October 15, =
> 2009 4:13=20
>  PM
>  
Subject: Re: Torsion =
> Seismometer in a=20
>  jar
>  

 face=3DArial>
>  

>  
In a message dated 15/10/2009 21:27:46 GMT Daylight Time,   href=3D"mailto:kevin.mckee@.......">kevin.mckee@....... =
> writes:
>    style=3D"BORDER-LEFT: blue 2px solid; PADDING-LEFT: 5px; MARGIN-LEFT: =
> 5px">    style=3D"BACKGROUND-COLOR: transparent" color=3D#000000 size=3D2 =
> face=3DArial>There=20
>    seemed to be some concern that the system would perform poorly or be =
> very=20
>    noisy. There was some discussion over the LED being a cause for =
> noise. I=20
>    used various incandescent bulbs, LEDs and sensors, and in some =
> cases, locked=20
>    the pendulum in a stationary position to test whether the sensor was =
> picking=20
>    up noise from the LED. In fact, I got a flat line even when the =
> amplifier=20
>    was maxed out--the LED was significantly quieter than other light =
> sources.=20
>    

>  

>  
Hi Kevin,
>  
 
>  
    You seem to be experiencing apparatus =
> problems.=20
>  Ordinary LEDs are much more noisy than superbright or IR LEDs. Both =
> vary in=20
>  light output by about x5 between 0 and 100 C. The is a HUGE variation. =
> They=20
>  are both more noisy than a filament bulb driven from a regulated =
> voltage=20
>  source. Your flat line response was probably due to low gain. You =
> should be=20
>  able to pick up microseisms all the time.
>  
    You can build a very good detector using =
> two=20
>  large area Si photocells BPW34 connected to a differential amplifier. =
> I get a=20
>  noise level of about 14 nano metres. You can't get adequate stability =
> with a=20
>  single detector or with a LED which is not temperature compensated.=20
>  Phototransistors are extremely noisy compared to photodiodes. You can =
> get very=20
>  fine Nichrome wire which makes a good suspension. Alternatively, =
> you can=20
>  use a single glass or carbon filament. 
>  
 
>  
    Regards,
>  
 
>  
    Chris Chapman
>  
 
>  
    
>
> ------=_NextPart_000_000A_01CA4DBB.8E711840--
>
>
>
> .------ ------ ------ ------ ------ ------ ------ ------ ------ ------.
> | Message 4                                                           |
> '------ ------ ------ ------ ------ ------ ------ ------ ------ ------'
> Subject: Re: Torsion Seismometer in a jar
> From:    ChrisAtUpw@.......
> Date:    Thu, 15 Oct 2009 21:49:17 EDT
>
>
> -------------------------------1255657757
> Content-Type: text/plain; charset="US-ASCII"
> Content-Transfer-Encoding: 7bit
>
>
> In a message dated 16/10/2009, tchannel@............ writes:
>
> Hi Chris,  the two large area Si photocells BPW34 connected to a
> differential amplifier, sound like something I would like to try.  Could 
> you help me
> with a simple schematic of this, even a sketch?   Does  the amp just use
> easy to find op amps?
>
> Thanks, Ted
>
>
>
> Hi Ted,
>
>    Check out the notes and the circuit at
> _http://jclahr.com/science/psn/chapman/photo_detect/index.html_
> (http://jclahr.com/science/psn/chapman/photo_detect/index.html)
>    This circuit works fine. You need the INA118 or  similar to get the
> very high CMRR common mode rejection ratio. You may need to  alter filter
> values to suit your application. The photocells drive current into  the 
> opamps,
> so they run at 0V and there is no leakage current. I usually use  a 
> miniature
> filament bulb driven from a stabilised voltage and a lens to  give a
> ~parallel light beam. You can use an IR LED if you provide an auxiliary 
> Si
> photodiode and a feedback amplifier to stabilise the photo output. 
> Otherwise  it
> drifts all over the place. I use two small razor blades for the sides of 
> the
> shutter, painted matt black, but with clean edges. They move just clear of
> the  surface of the photocells.  I measured the noise level at about 14 
> nano
> metres. There is inevitably some heat associated with the bulb. I suggest
> placing the bulb in a separate housing on top of the sensor. You under run
> the  bulb voltage supply to give ~infinite life.
>
>    Regards,
>
>    Chris Chapman
>
> -------------------------------1255657757
> Content-Type: text/html; charset="US-ASCII"
> Content-Transfer-Encoding: quoted-printable
>
> 
> 
> 
> 
>  id=3Dr=
> ole_body=20
> bottomMargin=3D7 leftMargin=3D7 rightMargin=3D7 topMargin=3D7> id=3Dr=
> ole_document=20
> color=3D#000000 size=3D2 face=3DArial>
> 

> 
In a message dated 16/10/2009, tchannel@............ writes:
>  style=3D"BORDER-LEFT: blue 2px solid; PADDING-LEFT: 5px; MARGIN-LEFT: 
> 5px"=
>>  style=3D"BACKGROUND-COLOR: transparent" color=3D#000000 size=3D2 face=3D=
> Arial>
>  
Hi Chris,  the two large area Si photocells BPW34 connected to=
> a=20
>  differential amplifier, sound like something I would like to try. =
> Could=20
>  you help me with a simple schematic of this, even a sketch?  =
> Does=20
>  the amp just use easy to find op amps?
>  
 
>  
Thanks, Ted
> 

> 
Hi Ted,
> 
 
> 
    Check out the notes and the circuit at 
>  =
>  href=3D"http://jclahr.com/science/psn/chapman/photo_detect/index.html">htt=
> p://jclahr.com/science/psn/chapman/photo_detect/index.html
> 
    This circuit works fine. You need the INA118=
> or=20
> similar to get the very high CMRR common mode rejection ratio. You may 
> nee=
> d to=20
> alter filter values to suit your application. The photocells drive 
> current=
> into=20
> the opamps, so they run at 0V and there is no leakage current. I usually=
> use=20
> a miniature filament bulb driven from a stabilised voltage and a 
> lens=
> to=20
> give a ~parallel light beam. You can use an IR LED if you provide an 
> auxil=
> iary=20
> Si photodiode and a feedback amplifier to stabilise the photo output. 
> Othe=
> rwise=20
> it drifts all over the place. I use two small razor blades for the sides=
> of the=20
> shutter, painted matt black, but with clean edges. They move just clear 
> of=
> the=20
> surface of the photocells.  I measured the noise level at about 14 
> na=
> no=20
> metres. There is inevitably some heat associated with the bulb. I suggest=
> =20
> placing the bulb in a separate housing on top of the sensor. You under 
> run=
> the=20
> bulb voltage supply to give ~infinite life. 
> 
 
> 
    Regards,
> 
 
> 
    Chris Chapman
>
> -------------------------------1255657757--
>
>
> .------ ------ ------ ------ ------ ------ ------ ------ ------ ------.
> | Message 5                                                           |
> '------ ------ ------ ------ ------ ------ ------ ------ ------ ------'
> Subject: Re: Torsion Seismometer in a jar
> From:    "Geoffrey" 
> Date:    Thu, 15 Oct 2009 19:07:15 -0700
>
> If you used a current source to keep a steady
> 10ma or 20 ma to the LED would that not be
> adequate stability for the light output also ?
>
>
> ----- Original Message ----- 
> From: "tchannel" 
> To: 
> Sent: Thursday, October 15, 2009 4:18 PM
> Subject: Re: Torsion Seismometer in a jar
>
>
> Hi Chris,  the two large area Si photocells BPW34 connected to a 
> differential amplifier, sound like something I would like to try.
> Could you help me with a simple schematic of this, even a sketch?   Does 
> the amp just use easy to find op amps?
>
> Thanks, Ted
>  ----- Original Message ----- 
>  From: ChrisAtUpw@.......
>  To: psn-l@..............
>  Sent: Thursday, October 15, 2009 4:13 PM
>  Subject: Re: Torsion Seismometer in a jar
>
>
>  In a message dated 15/10/2009 21:27:46 GMT Daylight Time, 
> kevin.mckee@....... writes:
>    There seemed to be some concern that the system would perform poorly or 
> be very noisy. There was some discussion over the LED
> being a cause for noise. I used various incandescent bulbs, LEDs and 
> sensors, and in some cases, locked the pendulum in a stationary
> position to test whether the sensor was picking up noise from the LED. In 
> fact, I got a flat line even when the amplifier was maxed
> out--the LED was significantly quieter than other light sources.
>
>  Hi Kevin,
>
>      You seem to be experiencing apparatus problems. Ordinary LEDs are 
> much more noisy than superbright or IR LEDs. Both vary in
> light output by about x5 between 0 and 100 C. The is a HUGE variation. 
> They are both more noisy than a filament bulb driven from a
> regulated voltage source. Your flat line response was probably due to low 
> gain. You should be able to pick up microseisms all the
> time.
>      You can build a very good detector using two large area Si photocells 
> BPW34 connected to a differential amplifier. I get a
> noise level of about 14 nano metres. You can't get adequate stability with 
> a single detector or with a LED which is not temperature
> compensated. Phototransistors are extremely noisy compared to photodiodes. 
> You can get very fine Nichrome wire which makes a good
> suspension. Alternatively, you can use a single glass or carbon filament.
>
>      Regards,
>
>      Chris Chapman
>
>
>
>
> .------ ------ ------ ------ ------ ------ ------ ------ ------ ------.
> | Message 6                                                           |
> '------ ------ ------ ------ ------ ------ ------ ------ ------ ------'
> Subject: Re: Torsion Seismometer in a jar
> From:    ChrisAtUpw@.......
> Date:    Thu, 15 Oct 2009 22:12:32 EDT
>
>
> -------------------------------1255659152
> Content-Type: text/plain; charset="US-ASCII"
> Content-Transfer-Encoding: 7bit
>
>
> In a message dated 16/10/2009, gmvoeth@........... writes:
>
> If you  used a current source to keep a steady
> 10ma or 20 ma to the LED would that  not be
> adequate stability for the light output also  ?
>
>
>
> Hi Geoff,
>
>    No chance. The photo output at a constant current  depends on the
> junction temperature.
>
>    Regards,
>
>    Chris Chapman
>
> -------------------------------1255659152
> Content-Type: text/html; charset="US-ASCII"
> Content-Transfer-Encoding: quoted-printable
>
> 
> 
> 
> 
>  id=3Dr=
> ole_body=20
> bottomMargin=3D7 leftMargin=3D7 rightMargin=3D7 topMargin=3D7> id=3Dr=
> ole_document=20
> color=3D#000000 size=3D2 face=3DArial>
> 

> 
In a message dated 16/10/2009, gmvoeth@........... writes:
>  style=3D"BORDER-LEFT: blue 2px solid; PADDING-LEFT: 5px; MARGIN-LEFT: 
> 5px"=
>>  style=3D"BACKGROUND-COLOR: transparent" color=3D#000000 size=3D2 face=3D=
> Arial>If you=20
>  used a current source to keep a steady
10ma or 20 ma to the LED would=
> that=20
>  not be
adequate stability for the light output also=20
> ?

> 

> 
Hi Geoff,
> 
 
> 
    No chance. The photo output at a constant 
> cur=
> rent=20
> depends on the junction temperature.
> 
 
> 
    Regards,
> 
 
> 
    Chris Chapman
>
> -------------------------------1255659152--
>
>
> .------ ------ ------ ------ ------ ------ ------ ------ ------ ------.
> | Message 7                                                           |
> '------ ------ ------ ------ ------ ------ ------ ------ ------ ------'
> Subject: Re: Torsion Seismometer in a jar
> From:    =?ISO-8859-1?Q?J=F3n_Fr=EDmann?= 
> Date:    Fri, 16 Oct 2009 04:04:54 +0000
>
> Hi,
>
> Is is possible to edit this design so it doesn't use glass jar and other
> weak material ?
>
> Regards,
> J=F3n Fr=EDmann.
>
> On fim, 2009-10-15 at 16:27 -0400, kevin.mckee@....... wrote:
>> Hi -
>> I just joined this e-mail list, and noticed some of the discussion about 
>> =
> the seismometer project I posted at 
> http://tinkeringcaveman.googlepages.com=
> /home
>>=20
>> There seemed to be some concern that the system would perform poorly or 
>> b=
> e very noisy. There was some discussion over the LED being a cause for 
> nois=
> e. I performed a number of tests before I completed the seismometer 
> (severa=
> l years ago now) to satisfy my own concerns in that regard. I used various 
> =
> incandescent bulbs, LEDs and sensors, and in some cases, locked the 
> pendulu=
> m in a stationary position to test whether the sensor was picking up noise 
> =
> from the LED. In fact, I got a flat line even when the amplifier was maxed 
> =
> out--the LED was significantly quieter than other light sources.=20
>>=20
>> I've actually found the two devices that I've built (facing 
>> orthogonally)=
> to be very sensitive.  I've put together a rough distance-magnitude 
> thresh=
> old detection plot that I can forward to anyone who is interested. The 
> weak=
> est quake I've detected is a magnitude 2.0, about 0.05 degrees (about 3 
> mil=
> es) away.  The common phases are easily picked out of the signal, 
> depending=
> on the quake origin.=20
>>=20
>> The larger factor in the devices' sensitivity is that I mounted them on 
>> a=
> basement slab under the stairs to my front porch, which means that  they 
> d=
> etects the comings and goings of my family too (I sometimes used this fact 
> =
> to check up on my daughters' returns from dates).
>>=20
>> I believe that I am detecting microseismic background with the 
>> instrument=
> too, rather than air currents.=20
>>=20
>> Regarding the fact that the sensor is a displacement sensor vice a 
>> veloci=
> ty sensor--I don't see that as a problem. As with a capacitive /radio 
> frequ=
> ency force-balance sensor, electronic filters and amplifiers can be used 
> to=
> translate the signal into a velocity response, if that is what is 
> desired.=
> In fact using the appropriate filter amplifier combination gets around 
> any=
> concerns like those expressed about the resolution of the optical sensing 
> =
> devices--electronic integration works very well for that.
>>=20
>>=20
>> Kevin McKee, Burke, VA
>> __________________________________________________________
>>=20
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>>=20
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>
>
>
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