capaNCDT 6100 - Micro-Epsilon

Functional Principle, Technical Data2.2.1Functional Principle, Technical DataMeasuring PrincipleThe principle of capacitive distance measurement with the capaNCDT system is based on the principle of theparallel 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 isproportional to the distance between the capacitor electrodes. The AC voltage is demodulated, amplified andoutput as an analog signal.The capaNCDT system evaluates the reactance X cof the plate capacitor which changes strictly in proportionto the distance.1areaX c = ; capacitance C = * *jCr o distanceThis theoretical relationship is realized almost ideallyin practice by designing the sensors as guard ringcapacitors.The linear characteristic of the measuring signal isachieved for electrically conductive target materials(metals) without any additional electronic linearization.Slight changes in the conductivity or magnetic propertiesdo not affect the sensitivity or linearity.GroundScreening electrodeMeasuring electrodeElectrical conductorFig. 1 Functional principle of the guard ringcapacitorcapaNCDT 6100Page 38