Practical and simple circuitry for the measurement of small capacitance.
Practical and cost-effective circuitry with high sensitivity has been developed to measure a small capacitance using current compensation method. The circuitry uses an electronic switch to periodically connect or separate the capacitor under test (C(x)) from a reference capacitor (C(r)). When C(x) is connected in parallel with C(r) the total capacitance becomes C(x)+C(r). On the other hand, as C(x) is separated from C(r), the total capacitance is only C(r). This periodic change of the capacitance generates a periodic square-wave output with an amplitude in proportion to the capacitance of C(x). A high sensitivity of DeltaV/DeltaC=202.2 mV/pF has been achieved, making the circuitry a powerful tool in measuring small capacitances. Three applications have been performed to present its capability: (a) displacement, (b) height of liquid, and (c) angle of tilt. The experimental results demonstrate the performance of the circuitry.
Lin
D Y
DY
Department of Electronic Engineering, National Changhua University of Education, Changhua 500, Taiwan, Republic of China. dylin@cc.ncue.edu.tw
Wu
J D
JD
Chang
Y J
YJ
Wu
J S
JS
D025802:Electric Capacitance; D004553:Electric Conductivity; D012680:Sensitivity and Specificity; D012984:Software