Hi,

my Krone-Hite 3322 is a standard band pass filter.  The low pass can be 
either "max flat" or RC, I have max flat seletected.  The high pass is 
just high pass.  Each half can have either 0 or 20db gain, I have 20db 
selected for both halves of the filter.  The bands can be set as low as 
1 milliHertz and as high as 99 KHz.  My A/D is set to 125 microVolts per 
data number.  The geophone, as far as I can remember, has an internal 
resister, so presumably it is set up for 4.5 Hz.

So perhaps not ideal.  I might have to save up my Euros...

Cheers

Ian

ChrisAtUpw@....... wrote:

>>>  I have a Mark Products L10B geophone. It has a metal case and is fairly well sealed. The lowest temperatures we normal get here is -10 C and inside the enclosure it will be slightly warmer.
>>>      
>>>
>
>Hi Ian,
>
>     Those temperatures should not be a any problem at all.
>
>  
>
>>>  The SEQUA10 looks interesting, though there isn't much detail on the webside. Does it work by just boosting the lower frequencies?  
>>>      
>>>
>
>     You set up your geophone to be critically damped. The additional amplifier has a frequency selective gain which tailors into the damping curve. The gain down to 1/10 the natural resonance is increased to a max of x100 to compensate for the f^2 natural rolloff. The overall response stays flat with velocity from 0.5 Hz to your low pass filter rolloff of maybe 10 Hz. Below 0.5 Hz the amplification falls off sharply again.
>
>  
>
>>>  If so, I can adjust my programmable filter to do the same thing, never thought about that...  Presumably this lowers the overall sensitivity of the device(?). Would you move the upper frequency down too or keep it just above its natural frequency - 4.5 Hz?
>>>      
>>>
>
>     You will quickly run into digitisation step / noise problems if you try to do it that way, unless you have the overall amplifier gain set WAY UP. Can you even set up your filter to have a reciprocal f^2 response reducing to unity at about 9 Hz and falling again below 0.5 Hz? The overall output voltage sensitivity stays the same, just the bandwidth is increased. There is a small increase in the overall noise. The major ++ is being able to detect the P and S waves directly with a 4.5 Hz geophone. 
>
>     The original Roberts' circuit used a high pass filter which was still sensitive to 1/f VLF noise. Using a modified filter circuit has removed most of that noise.
>
>     Regards,
>
>     Chris Chapman
>__________________________________________________________
>
>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.
>
>  
>



  
  


Hi,



my Krone-Hite 3322 is a standard band pass filter.  The low pass can be
either "max flat" or RC, I have max flat seletected.  The high pass is
just high pass.  Each half can have either 0 or 20db gain, I have 20db
selected for both halves of the filter.  The bands can be set as low as
1 milliHertz and as high as 99 KHz.  My A/D is set to 125 microVolts
per data number.  The geophone, as far as I can remember, has an
internal resister, so presumably it is set up for 4.5 Hz.



So perhaps not ideal.  I might have to save up my Euros...



Cheers



Ian



ChrisAtUpw@....... wrote:


  

    

      
  I have a Mark Products L10B geophone. It has a metal case and is fairly well sealed. The lowest temperatures we normal get here is -10 C and inside the enclosure it will be slightly warmer.
      
    
  
  

Hi Ian,

     Those temperatures should not be a any problem at all.

  
  

    

      
  The SEQUA10 looks interesting, though there isn't much detail on the webside. Does it work by just boosting the lower frequencies?  
      
    
  
  

     You set up your geophone to be critically damped. The additional amplifier has a frequency selective gain which tailors into the damping curve. The gain down to 1/10 the natural resonance is increased to a max of x100 to compensate for the f^2 natural rolloff. The overall response stays flat with velocity from 0.5 Hz to your low pass filter rolloff of maybe 10 Hz. Below 0.5 Hz the amplification falls off sharply again.

  
  

    

      
  If so, I can adjust my programmable filter to do the same thing, never thought about that...  Presumably this lowers the overall sensitivity of the device(?). Would you move the upper frequency down too or keep it just above its natural frequency - 4.5 Hz?
      
    
  
  

     You will quickly run into digitisation step / noise problems if you try to do it that way, unless you have the overall amplifier gain set WAY UP. Can you even set up your filter to have a reciprocal f^2 response reducing to unity at about 9 Hz and falling again below 0.5 Hz? The overall output voltage sensitivity stays the same, just the bandwidth is increased. There is a small increase in the overall noise. The major ++ is being able to detect the P and S waves directly with a 4.5 Hz geophone. 

     The original Roberts' circuit used a high pass filter which was still sensitive to 1/f VLF noise. Using a modified filter circuit has removed most of that noise.

     Regards,

     Chris Chapman
__________________________________________________________

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.