In a message dated 10/02/2008, PETERS_RD@.......... writes:

I've been able now to give enough thought to your comments about  "potholes" 
to
provide the following response.
Chris 'hit the nail on the  head' with his statement "... to cope with 
discrete steps in
the zero  level".  In other words, if the term is at all appropriate, it is 
not  your
'average' pothole as found in northern climate highways where  temperatures 
are at times
routinely below freezing.  The 'potholes of  seismic type' are 'diffusive' in 
terms of
both temperature and  stress.



Hi Brett,
 
    This raises another point about  practical seismometer performance. 
'Instantaneous' shifts in the zero level  generate wide bandwidth high amplitudes 
spikes in a velocity feedback loop.  These have to be applied using a coil with 
a high inductance and can  saturate the electronics. Using magnet + plate 
damping avoids this.
 
    Regards,
 
    Chris Chapman



   






In a message dated 10/02/2008, PETERS_RD@.......... writes:
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    I've been able now to give enough thought to your comments about=20
  "potholes" to
provide the following response.
Chris 'hit the nail on=
 the=20
  head' with his statement "... to cope with discrete steps in
the zero=20
  level".  In other words, if the term is at all appropriate, it is not=
=20
  your
'average' pothole as found in northern climate highways where=20
  temperatures are at times
routinely below freezing.  The 'potholes=
 of=20
  seismic type' are 'diffusive' in terms of
both temperature and=20
  stress.


Hi Brett,
 
    This raises another point about=20
practical seismometer performance. 'Instantaneous' shifts in the zero l=
evel=20
generate wide bandwidth high amplitudes spikes in a velocity feedback l=
oop.=20
These have to be applied using a coil with a high inductance and c=
an=20
saturate the electronics. Using magnet + plate damping avoids this.
 
    Regards,
 
    Chris Chapman