Bruce, A totally trivial correction for you : "the work of RV Jones at the university of Glasgow in the 50's, 60's and 70's. "
Jones was at Aberdeen university post war. A curious character, his recollections of his wartime research are fascinating and worth reading but I fear are best read with care alongside some other histories to maintain balance. Regards David > -----Original Message----- > Hej Magnus > > A capacitive sensing AC bridge can be very sensitive, one only has to > look at the work of RV Jones at the university of Glasgow in > the 50's, > 60's and 70's. He and his collaborators used capacitive sensors to > detect (among other things) the extrusion of a micrometer shaft as it > was clamped to realise just how sensitive it can be. > They found it possible to detect length changes of less than > 1E-11m with > a suitably designed sensor. > > Even more sensitive capacitance bridge displacement sensors > have since > been constructed. Off course the critical bridge components > have to be > maintained at a reasonably constant temperature. Since the > most critical > component the balancing capacitor in the other bridge arm can be very > small it can easily be located in the same controlled temperature > environment as the sensor itself. One of the major contributors to > instability will be creep in the glass capillary and bulb dimensions. > Even with a relatively crude guard ringed coaxial sensor electrode > surrounding a capillary tube is capable of submicron > sensitivity without > undue effort. > > If one uses a mercury in glass thermometer with say 0.1C > resolution with > the 0.1C graduation say 0.5mm apart then 1micron change in mercury > column length is equivalent to a temperature change of 200uK. The > performance will be determined largely by mechanical > instabilities not > the bridge sensitivity. > > Bruce _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
