Combination sensor enables non-contact, one-sided thickness measurements of plastic film and coated metals

Precision sensor manufacturer Micro-Epsilon has launched a new sensor system that combines an eddy current sensor with a capacitive displacement sensor in a single housing.

This sensor concept enables high precision one-sided thickness measurements of plastic film or coatings applied on metal objects, plates or sheets.



The new combiSENSOR from Micro-Epsilon combines two non-contact displacement measuring principles: eddy current and capacitive, which together enable high precision one-sided thickness measurements of electrically non-conductive materials.

The sensor is ideally suited to applications in the plastics industry to determine the thickness of plastic film, plastic coatings on metals, as well as applied adhesives on felt or tapes.

Connected to the sensor via a cable, the combiSENSOR controller processes and calculates the signals in order to output these via digital interfaces.

Calculation of the two sensor signals compensates for any mechanical changes to the target object/material, such as thermal expansion, deflections or eccentricity.

Due to the redundancy of this combined sensor measuring principle, the measured thickness value remains unaffected by any changes in the measurement set up.

Due to the high temperature stability of the combiSENSOR, the system provides high measurement accuracy even in fluctuating temperatures.

Measuring principle

The design of the eddy current measurement coil and the capacitive measurement electrodes is concentric. Both sensors measure against the same spot.

The signal of the capacitive displacement sensor is a function of the working distance, the thickness of the insulator (D) and the dielectric constant of the insulator material (εr).

At the same time, the eddy current displacement sensor measures the distance to the ground electrode (eg, metal sheet or metal roller positioned behind the film).

The controller outputs both signals as well as the difference between the capacitive sensor and eddy current sensor.

Also, the dielectric constant can be calculated with known thickness and working distance.

An intuitive web interface simplifies set up and configuration of the sensor.

The controller also features digital Ethernet and EtherCAT interfaces for easy integration into the user’s own production control environment.

Measuring ranges of the combiSENSOR are 5mm and 10mm. Target thickness is 40µm to max. 6mm. Linearity of the system is ± 0.05%. Measuring speed is up to 1kHz (analogue), with a maximum of 3.9kS/s (digital).

The sensor operates within a temperature range of -10°C to +85°C.