Functional Principle, Technical Data; Measuring Principle - MICRO-EPSILON capaNCDT 6240 Operating Instructions Manual

Functional Principle, Technical Data

2. Functional Principle, Technical Data
2.1

Measuring Principle

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 electrodes.
If a constant AC current flows through the sensor capacitor, the amplitude of the AC voltage at the sensor is proportional to the dis-
tance between the capacitor electrodes. The AC voltage is demodulated, amplified and output as an analog signal.
The capaNCDT system evaluates the reactance X
1
= ;
X capacitance C =  *  *
c
j C
i
A small target and bent (uneven) surfaces cause a non-linear characteristic.
This theoretical relationship is realized almost ideally in
practice by designing the sensors as guard ring capaci-
tors.
The linear characteristic of the measuring signal is
achieved for electrically conductive target materials
(metals) without any additional electronic linearization.
Slight changes in the conductivity or magnetic proper-
ties do not affect the sensitivity or linearity.
capaNCDT 6240
of the plate capacitor which changes strictly in proportion to the distance.
C
area
r
o
distance
Electrical conductor
Fig. 1 Functional principle of the guard ring
capacitor
Ground
Screening electrode
Measuring electrode
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