[time-nuts] Capacitive temperature sensing

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Aug 23 06:57:35 EDT 2008

Hej Magnus

An elegant way of achieving some degree of temperature compensation may 
be to use 3 coaxial electrodes surrounding the mercury column.
One relatively long one used to couple the bridge drive signal to the 
mercury column and located between the other 2. The top electrode one 
being used to sense the position of the tip of the mercury column and 
the lower one as a temperature compensation element in the other side of 
the bridge.
A phase sensitive detector with a suitable preamp could be used to 
detect a capacitive null.
The phase sensitive detector output drives a PID or other temperature 
control system.


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