Sophisticated thickness measurement using dual-sensor technique

Sensors can be used for many different applications. However, in the measurement of plate and film thickness, many sensors soon reach their performance limit and can only solve this measurement problem by using more complex systems. The linking of two sensors based on different measurement principles opens up completely new applications. The developer, Micro-Epsilon, combines these sensors under the name ‘dual-sensor technique’. Sensors with a particular measurement principle have very specific strengths. For example, a capacitive sensor measures very precisely, but reacts sensitively to materials in the measurement gap. If two different sensors are combined, their specific strengths can be applied. Restrictions and interference that would normally occur with one sensor, can now be offset using the other sensor, resulting in higher accuracy measurement systems.

In one of many models developed by the manufacturer, a laser triangulation sensor is combined with an eddy current sensor. These types of sensors are used to measure the layer thickness of different plastics during production. For this application, a special eddy current sensor with two holes in the centre of the sensor, is mounted in front of the optical system of the laser sensor. The laser beam measures through the holes onto the plastic surface on the same axis as the eddy current sensor. The electromagnetic field of the eddy current sensor penetrates the plastic layer and measures with respect to a metal reference material located underneath it. This could,for example, be a metal form in the measurement of sprayed coating thickness in production or a metal roller over which a web-shaped plastic is passed. Following evaluation, software calculates the thickness of the measurement object from the two sensor signals.

For this dual-sensor technology, the company only uses in-house sensors, software and mechanical systems.

There are dual sensors in many other combinations. For example, the company also offers combinations of capacitive sensors or sensors operating on the shadow-principle with eddy current sensors. The most frequent application for dual-sensors is the thickness measurement of various materials. Apart from foam materials, non-vulcanised rubber, extruded and rolled films, seal profiles, chipboards and conducting materials, such as metal tracks and circuit boards can also be inspected for material thickness.