----- Original Message -----=20
  From: Bobhelenmcclure@..........
  To: psn-l@.................
  Sent: Wednesday, August 14, 2002 8:20 PM
  Subject: DRIP (diamagnetically restored inverted pendulum)


  My present device is lacking the necessary position sensors, so I can =
tell you nothing about its performance as a tiltmeter type seismometer.  =
That will have to come later.  It should be able to sense horizontal =
ground motion and direction, if fitted out with a pair of othogonally =
oriented position sensors.

  A suggestion from George Harris

  A very sensitive and inexpensive two axis sensor can be made as =
follows:

  Above the top surface of the pendulum, place an LED with the front =
surface=20
  flattened so that it become a point source about 1/4 inch above the =
surface.
  On the top surface cement a 6mm square mirror (stock H43866 from =
Edmund).
  On each of the four sides of the LED place small solar cells (stock =
980-0150
  from allied) in such a position that each will be half illuminated by =
the LED.

  The photocells can be connected in parallel, plus to minus, on the =
opposite sides across the inputs to a low noise operational amplifier =
(like an OP27 from Precision monolithics) with about a megohm in the =
feedback.  The resulting output is very sensitive (nanometers) and =
linear.

  To check the sensitivity, I mounted the assembly on a three point =
platform with
  a dial indicator on one end of the platform.  Tilting the platform by =
small motions of a support screw permits the accurate measurement of the =
anglular (or acceleration) sensitivity.








 

  
----- Original Message ----- 
  From:=20
  Bobhelenmcclure@....... 
  
To: psn-l@.............. 
  
Sent: Wednesday, August 14, =
2002 8:20=20
  PM
  
Subject: DRIP (diamagnetically =
restored=20
  inverted pendulum)
  


  
My present device is lacking the necessary =
position=20
  sensors, so I can tell you nothing about its performance as a =
tiltmeter type=20
  seismometer.  That will have to come later.  It should be =
able to=20
  sense horizontal ground motion and direction, if fitted out with a =
pair of=20
  othogonally oriented position sensors.

  
A suggestion from George =
Harris
  
 
  
A very sensitive and inexpensive two axis sensor =
can be=20
  made as follows:
  
 
  
Above the top surface of the pendulum, place an =
LED with=20
  the front surface 
  
flattened so that it become a point source about =
1/4 inch=20
  above the surface.
  
On the top surface cement a 6mm square mirror =
(stock H43866=20
  from Edmund).
  
On each of the four sides of the LED place small =
solar=20
  cells (stock 980-0150
  
from allied) in such a position that each will be =
half=20
  illuminated by the LED.
  
 
  
The photocells can be connected in parallel, plus =
to minus,=20
  on the opposite sides across the inputs=20
  to a low noise operational amplifier (like an OP27 from Precision =
monolithics)=20
  with about a megohm in the feedback.  The resulting output is =
very=20
  sensitive (nanometers) and linear.
  
 
  
To check the sensitivity, I mounted =
the assembly=20
  on a three point platform with
  
a dial indicator on one end of the=20
  platform.  Tilting the platform by small motions of a support =
screw=20
  permits the accurate measurement of the anglular (or acceleration)=20
  sensitivity.