Hi Chris,  Thanks for the explanation.  Have they also use lasers, in =
such devises?   Ted
  ----- Original Message -----=20
  From: ChrisAtUpw@..........
  To: psn-l@.................
  Sent: Wednesday, April 04, 2007 3:54 PM
  Subject: Re: Tiltmeter progress


  In a message dated 2007/04/07, tchannel@.............. writes:


    Hi George,  This is interesting.  Where can I find articles to read =
more=20
    about the basic principle. etc.=20


  Hi Ted,

         See http://ntweb.mcn.org/gbush/Tiltmeter/tiltmeter%20Main.html =
for several references.
         This tiltmeter has two Perspex cups 2 ft apart on a baseplate, =
connected by plastic tube and part filled with Mercury. Two flat plates =
are suspended just above the Hg surfaces to form capacitative level =
detectors. The cup system is sealed to contain the Hg vapour, which is =
very poisonous and attacks electronic components, Cu wire, pcbs etc like =
fun.
         The original SciAm circuit used valves, a crystal oscillator =
and resonant tuned detectors followed by diode rectifiers. The =
oscillating voltages were quite high. The Nuts and Volts version was an =
adaptation of this to semiconductors, with lower voltages. The new N&V =
board seemed to suffer from AC hum from the on board PSU. A major =
problem with the whole concept is that the foreward voltage of rectifier =
diodes drifts by about 2.5 mV / C deg and the resonant circuits also =
drift with temperarure. So, unless you are very determined, you may end =
up with an expensive differential thermometer sensitive to random air =
movements and to any stray capacitance going. The work/satisfaction =
ratio may be discouraging.
         A good way around this ''problem'' is to redesign the circuit =
using a capacitative detector working at high audio frequencies, not at =
RF and to provide a FET phase sensitive detector. The LTC1043 IC has all =
the switching components on it. You can use the on chip oscillator, but =
I found that an external Crystal oscillator gave significantly better =
results. I used a 2.4576 M Hz AT cut crystal in a 4060 oscillator =
divider circuit, giving a 9.6 kHz drive.=20
         If you want to sense only earth tides and similar, severely =
damping the Hg flow will tend to reject any passing earthquakes, local =
delivery trucks, etc. Clamp a piece of cleaned iron wire centrally in =
the plastic tube containing the Hg, using an external clamp maybe 1" =
wide. Hg 'wets' the iron, but does not dissolve it, leaving two narrow =
triangular passages bounded by the plastic and the wire.

         Regards,








Hi Chris,  Thanks for the =
explanation. =20
Have they also use lasers, in such devises?   Ted

  
----- Original Message ----- 
  From:=20
  ChrisAtUpw@....... 
  
To: psn-l@.............. 
  
Sent: Wednesday, April 04, 2007 =
3:54=20
  PM
  
Subject: Re: Tiltmeter =
progress
  

In a=20
  message dated 2007/04/07, tchannel@..............=20
  writes:


  Hi George,  This is interesting.  Where can I =
find=20
    articles to read more 
about the basic principle. etc.=20
  

Hi =
Ted,

       See=20
  http:=
//ntweb.mcn.org/gbush/Tiltmeter/tiltmeter%20Main.html=20
  for several references.
       This =
tiltmeter=20
  has two Perspex cups 2 ft apart on a baseplate, connected by plastic =
tube and=20
  part filled with Mercury. Two flat plates are suspended just above the =
Hg=20
  surfaces to form capacitative level detectors. The cup system is =
sealed to=20
  contain the Hg vapour, which is very poisonous and attacks electronic=20
  components, Cu wire, pcbs etc like=20
  fun.
       The original SciAm =
circuit used=20
  valves, a crystal oscillator and resonant tuned detectors followed by =
diode=20
  rectifiers. The oscillating voltages were quite high. The Nuts and =
Volts=20
  version was an adaptation of this to semiconductors, with lower =
voltages. The=20
  new N&V board seemed to suffer from AC hum from the on board PSU. =
A major=20
  problem with the whole concept is that the foreward voltage of =
rectifier=20
  diodes drifts by about 2.5 mV / C deg and the resonant circuits also =
drift=20
  with temperarure. So, unless you are very determined, you may end up =
with an=20
  expensive differential thermometer sensitive to random air movements =
and to=20
  any stray capacitance going. The work/satisfaction ratio may be=20
  discouraging.
       A good way =
around this=20
  ''problem'' is to redesign the circuit using a capacitative detector =
working=20
  at high audio frequencies, not at RF and to provide a FET phase =
sensitive=20
  detector. The LTC1043 IC has all the switching components on it. You =
can use=20
  the on chip oscillator, but I found that an external Crystal =
oscillator gave=20
  significantly better results. I used a 2.4576 M Hz AT cut crystal in a =
4060=20
  oscillator divider circuit, giving a 9.6 kHz drive.=20
  
       If you want to sense only =
earth tides=20
  and similar, severely damping the Hg flow will tend to reject any =
passing=20
  earthquakes, local delivery trucks, etc. Clamp a piece of cleaned iron =
wire=20
  centrally in the plastic tube containing the Hg, using an external =
clamp maybe=20
  1" wide. Hg 'wets' the iron, but does not dissolve it, leaving two =
narrow=20
  triangular passages bounded by the plastic and the=20
  wire.

      =20
  Regards,

       Chris =
Chapman=20