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 (Cx) from a reference capacitor (Cr). When Cx is connected in parallel with Cr the total capacitance becomes Cx+Cr. On the other hand, as Cx is separated from Cr, the total capacitance is only Cr. This periodic change of the capacitance generates a periodic square-wave output with an amplitude in proportion to the capacitance of Cx. A high sensitivity of ΔVΔC=202.2mVpF 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.

1.
F. N.
Toth
,
G. C. M.
Meijer
, and
M.
van der Lee
,
IEEE Trans. Instrum. Meas.
46
,
644
(
1997
).
2.
S. P.
Chang
and
M. G.
Allen
,
Sens. Actuators, A
116
,
195
(
2004
).
3.
C.
Acer
and
A. M.
Shkel
,
J. Micromech. Microeng.
13
,
634
(
2003
).
4.
N.
Reinecke
and
D.
Mewes
,
Meas. Sci. Technol.
46
,
233
(
1996
).
5.
N. C.
Bruce
and
A. G.
Valenzuela
,
Meas. Sci. Technol.
16
,
669
(
2005
).
6.
J.
Tapson
and
J. R.
Greene
,
Meas. Sci. Technol.
5
,
20
(
1994
).
7.
P.
Holmberg
,
IEEE Trans. Instrum. Meas.
44
,
803
(
1995
).
8.
M. A.
Atmanand
,
V. J.
Kumar
, and
V. G. K.
Murti
,
IEEE Trans. Instrum. Meas.
44
,
898
(
1995
).
You do not currently have access to this content.