From: Geoff 

To: psnlist 
Sent: Tue, 1 Jan 2013 6:40
Subject: Re: Omnidirectional instrument


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On 12/31/2012 11:32 AM,      Tangazazen@....... wrote:
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Hi Geoff,
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Curiously enough I was interested at one time in a omni          directiona=
l seismometer but also wanted directional          information. What I ende=
d up with was a pendulum with 2          degrees of freedom which via a qua=
drant photo cell resolved           the N-S,  E-W  component independently.=
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Regards Martin
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    I like the photocell idea also i guess i might try a CdS photo resistiv=
e element.
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Hi Geoff,

    CdS photocells do not have the linearity, the temperature coefficient, =
or the frequency=20
response to work well and you can't buy matched pairs. You would be wasting=
 your time,=20
money and effort !=20
    I have used inexpensive BPW34 Silicon photocells to give a resolution=
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of about 14 nano metres in a seismic sensor.  =20

    Regards,=20

    Chris Chapman
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From: Geoff <gmvoeth@gma=
il.com>







To: psnlist <psnlist@..............>




Sent: Tue, 1 Jan 2013 6:40




Subject: Re: Omnidirectional instrument






















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On 12/31/2012 11:32 AM,
      Tangazazen@....... wrote:





    




    

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Hi Geoff,




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Curiously enough I was interested at one time in a omni
          directional seismometer but also wanted directional
          information. What I ended up with was a pendulum with 2
          degrees of freedom which via a quadrant photo cell resolved 
          the N-S,  E-W  component independently. 





        




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Regards Martin




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    I like the photocell idea also i guess i might try a CdS photo resistiv=
e element.





    



Hi Geoff,







    CdS photocells do not have the linearit=
y, the temperature coefficient, or the frequency 

response to work well and you can't buy matched pairs. You would be wasting=
 your time, 

money and effort =
! 

    I have used inexpe=
nsive BPW34 Silicon photocells to give a resolution 

of about 14 nano metres in a seismic sensor.  =
 



    Regards, 



    Chris Chapman





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