In a message dated 17/12/02, lconklin@............ writes:

> I've been thinking about building a vertical sensor.  One design I've been
> considering would use a bowed leaf spring similar to the Sean-Thomas
> Morisssey design, combined with the differential capacitor sensor using
> Larry's SG electronics board.  I'd be interested in hearing whether anyone
> else has tried this or if anyone has any thoughts regarding the viability of
> this approach.

Hi Larry,

       The SG oscillator / capacitor / tuned circuit design is quite 
temperature sensitive and the technique is 'out of date', by maybe twenty 
years. Allan Coleman has a good capacitor sensor design on his Website. There 
is also one capacitor bridge design in the Linear Technology archive notes 
dated early '96, "Bridge Measures Small Capacitance" by Jeff Witt. There are 
several subsequent designs for capacitance measurement, but they seem 
designed to actually measure capacity, rather than be useful as a 
differential movement sensor. (The capacity is inversely proportional to the 
separation of the plates, which is what you are interested in.) 
Alternatively, you could use a modified NE5521 LVDT circuit with a fet 
amplifier on the sense input. They work pretty well.
  
       Leaf springs tend to suffer from fewer resonance problems than coil 
springs. Again, why not have a look at Allan's design for a vertical? His 
MKXV vertical is a compact and most interesting design. 

       Regards,

       Chris Chapman
In a message dated 17/12/02, lconklin@............ writes:



I've been thinking about building a vertical sensor.  One design I've been

considering would use a bowed leaf spring similar to the Sean-Thomas

Morisssey design, combined with the differential capacitor sensor using

Larry's SG electronics board.  I'd be interested in hearing whether anyone

else has tried this or if anyone has any thoughts regarding the viability of

this approach.




Hi Larry,



       The SG oscillator / capacitor / tuned circuit design is quite temperature sensitive and the technique is 'out of date', by maybe twenty years. Allan Coleman has a good capacitor sensor design on his Website. There is also one capacitor bridge design in the Linear Technology archive notes dated early '96, "Bridge Measures Small Capacitance" by Jeff Witt. There are several subsequent designs for capacitance measurement, but they seem designed to actually measure capacity, rather than be useful as a differential movement sensor. (The capacity is inversely proportional to the separation of the plates, which is what you are interested in.) Alternatively, you could use a modified NE5521 LVDT circuit with a fet amplifier on the sense input. They work pretty well.

  

       Leaf springs tend to suffer from fewer resonance problems than coil springs. Again, why not have a look at Allan's design for a vertical? His MKXV vertical is a compact and most interesting design. 



       Regards,



       Chris Chapman