A fast charge-meter for interfacing capacitive sensors

This paper presents a fast charge-meter as an electronic interface for multiple capacitive sensors with maximum value lpF. A cable capacitance of up to InF can be tolerated. Two different modes of measurement are available - a normal mode and a fast mode. The conversion time is 39 mus and 64 mus for the fast and for the normal mode, respectively. The resolution in normal mode, with cable capacitance less than 400 pF, is better than 14 bits. A special multi-slope A-to-D conversion is used, which, to increase the resolution, at the beginning and at the end of the conversion process transfers itself into an over-sampling conversion. The interface is realized on a PCB with a single euro-board format. Six sensors can be interfaced in programmable sequence. The power consumption is less than 1 W.

[1]  Kenzo Watanabe,et al.  A switched-capacitor charge-balancing analog-to-digital converter and its application to capacitance measurement , 1987, IEEE Transactions on Instrumentation and Measurement.

[2]  Boby George,et al.  Switched capacitor triple slope capacitance to digital converter , 2006 .

[3]  Maurice Beck,et al.  REVIEW ARTICLE: Electronic transducers for industrial measurement of low value capacitances , 1988 .

[4]  F. Krummenacher.  A High Resolution Capacitance-to-Frequency Converter , 1984, ESSCIRC '84: Tenth European Solid-State Circuits Conference.

[5]  Gerard C. M. Meijer,et al.  A novel low-cost capacitive-sensor interface , 1996 .

[6]  F. Reverter,et al.  A low-cost microcontroller interface for low-value capacitive sensors , 2004, Proceedings of the 21st IEEE Instrumentation and Measurement Technology Conference (IEEE Cat. No.04CH37510).