Bruce Griffiths <[EMAIL PROTECTED]> wrote: >Mike
> One good general reference for capacitance micrometers is: > /Microdisplacement Transducers/ by P.H. Sydenham, Journal of > Physics E, Scientific Instruments, Vol 5, p721-33, 1972. ><Microdisplacement+Transducers%EF%BF%BD+by+P.H.+Sydenham,%20Journal%20of%20Physics%20E,%20Scientific%20Instruments,%20Vol%205,%20p721-33,+1972.> > It seems that capacitance micrometers can be 3 orders of magnitude > more sensitive than I stated i.e. they can detect displacements of > about 1E-14 m. > This compares well with interferometry which can detect > displacements of around 1E-10 m. > RV Jones was at the University of Aberdeen not Glasgow. > RV Jones was the first recipient of the CIA's RV Jones > Intelligence award: >http://www.royalsoced.org.uk/fellowship/obits/obits_alpha/jones_reginald.pdf >http://www.iop.org/EJ/abstract/0022-3735/6/7/001/ > Bruce Hi Bruce, Thanks very much for the url. That is a very interesting article on Jones. Nice to have an award named after you, and to be the first one to receive it:) The abstract for his article states: "A general account is given of both the electrical and the mechanical aspects of the design of capacitive transducers and their associated electronic circuitry suitable for observing displacements of the order 10-2 to 10-11 mm. The lower figure is the order of magnitude of noise and drift averaged over a second, the drift over a day of the order 10-8 to 10-9 mm. Their application is illustrated by descriptions of an apparatus to explore the limits of performance, a moderately sensitive micrometer, and two geophysical instruments, a tiltmeter and a gravimeter. Full details of a general purpose electronic system are given." That article, and "Microdisplacement Transducers" by Sydenham both cost $80.00 USD. That's a bit high. It's a shame they have to charge so much, when the internet has reduced the distribution cost to nearly zero. It's not very useful to claim a resolution of 10-11mm when that is the magnitude of noise and drift averaged over a second. The drift of 10-9mm per day is more realistic, but I'd really like to see the drift expected per year. Probably the capacitive sensor has the best application in measuring dynamic issues such as the roundness of rotating shafts, tiltmeters, and other areas where interferometry is difficult or cannot be used. But for short-term measurements, it looks very good. Thanks for the info! Best Regards, Mike Monett _______________________________________________ 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.
