5Aragones R, Alvarez P, Oliver J, et al. A capacitance-to- frequency converters comparison for a frequency acquisi- tion platform [ M ]. NEW YORK: IEEE, 2010:1431 - 1436.
6Babu C, Somesh D H. Design of self-compensated non contact capacitive sensors and proficient signal condition- ing circuit for mult threshold liquid level control - a no- vel approach[ J]. 2006 IEEE International Conference on Industrial Technology, 2006 ( 1 - 6 ) :2541 - 2546.
7Seliskar D P, Waterbury R G, Kearney R E. Proportional microvolume capacitive liquid level sensor array [ M ]. NEW YORK: IEEE ,2005 :7258 - 7261.
