Functional Principle, Technical Data; Measuring Principle - MICRO-EPSILON capaNCDT 6110 IP Operating Instructions Manual

Functional Principle, Technical Data

2.
2.1
The principle of capacitive distance measurement with the capaNCDT system is based on the principle of the
parallel plate capacitor. For conductive targets, the sensor and the target opposite form the two plate elec-
trodes.
If a constant AC current flows through the sensor capacitor, the amplitude of the AC voltage at the sensor is
proportional to the distance between the capacitor electrodes. The AC voltage is demodulated, amplified and
output as an analog signal.
The capaNCDT system evaluates the reactance X
to the distance:
X =
i
This theoretical relationship is realized almost ideally
in practice by designing the sensors as guard ring
capacitors.
The linear characteristic of the measuring signal is
achieved for electrically conductive target materials
(metals) without any additional electronic lineariza-
tion. Slight changes in the conductivity or magnetic
properties do not affect the sensitivity or linearity.
capaNCDT 61xx/IP
Functional Principle, Technical Data

Measuring Principle

1
; capacitance C = 
c
jC
A small target and bent (uneven) surfaces cause a non-linear characteristic.
of the plate capacitor which changes strictly in proportion
C
area

* *
r
o
distance
Electrical conductor
Fig. 1 Functional principle of a capacitive sensor
Ground
Screening electrode
Measuring electrode
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