Thickness Measurement - MICRO-EPSILON combiSENSOR KSH5 Betriebsanleitung

Functional Principle, Technical Data
combiSENSOR
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2.1.3

Thickness Measurement

The main field of application is the traversing thickness measurement of plastic film or of
plastic coating on metal plates. Arithmetical coupling of the two sensor signals provides
compensation of mechanical changes, for example thermal expansion, deflections, eccentri-
city in the measurement device. Through the redundancy of this combined sensor principle,
the measured thickness value remains unaffected by any changes in the measurement
setup. The target thickness D is calculated from both sensor signals.
A1
T Insulator
Ground electrode
Fig. 2 Sensor arrangement for thickness measurement
The capacity of the measuring gap is calculated from the following factors: offset, thickness
of the target and the permittivity:
1
C
=

C
D
r
1 - (( ) (1 - ))
0 *

S
r
D: Thickness of the target
S: Offset = ( A + D)
e * e
: Permittivity air (e
1 0 r1
e * e
: Permittivity film (e
2 0 r2
A constant permittivity of the target is required in order to obtain correct measuring results.
In the case that the offset gets smaller, the percental signal change increases. However, in
practice there are limits to a very small offset for example due to material guiding.
Example:
KSH5, the sensor is mounted at offset of 4.5 mm, film thickness of 150 µm and e
the metal ground electrode.
The output signal on the capacitive sensor decreases by 2 %.
In contrast to the capacitive signal of the sensor, the output signal of the eddy current signal
is not being affected by the materials in the measuring gap and is therefore determined by
the distance between the sensor and the ground electrode.
Sensor
Target
1
U ~
;
C
)
)
of 2.5 on
r2
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