Re: [Phys-l] modern G measurement

[Brian Whatcott <betwys1@sbcglobal.net>]

John Denker wrote:
> Hi --
>
> Does anybody have experience with the TEL-Atomic Cavendish balance?
>   http://www.telatomic.com/mechanics/cavendish_balance.html
>   http://physics.mercer.edu/hpage/cav.html
It was good to see a 24 bit capacitance to digital conversion chip with 
a range of pF and
a resolution of aF and accuracy of fF at the heart of this device, 
rigged like a kind of quadrant electrometer with printed circuit 
differential plates... This is the AD 7745 chip.

 It set me to thinking of the WW2 researcher who worked on a 
capacitance bridge altimeter for aircraft with a plate on each wing - 
Blumlein, if I recall. What he could have done with this chip!  
And that reminded me of the 3 axis utility accelerometer chip that I 
just received.  The ADXL330 from the same shop as the capacitance device.
It uses 1 or 2 milliwatts -  good for +-3 g and with a noise floor 
around  90 uV /sqrtHz  and sensitivity around 300 mV/g on a 2 x 2 cm 
printed cct, for $20 or so.

People are using it with a microprocessor ($35) and an infra red 
horizon sensor ($low?) to make a useful autopilot for hobby drones at 
what was once an  unimaginably low price.    The single highest cost 
optional item is the GPS needed to execute a preprogrammed route.

Brian W