Various possibilities exist for the thickness measurement, including transmission processes, x-ray and infrared sensor technologies as well as the optical triangulation concept.
The measuring system consists of the top and bottom sensor. The bottom sensor includes a magnetic / eddy-current distance measuring system which measures the distance to a reference plate, which is part of the top sensor. The flat material between the two sensors affects the distance between the upper and lower part of the plates which yields the raw measurement signal.
This kind of thickness measurement is based on the comparison of the optical coating thicknesses with the wave lengths of the light. Light irradiated on a transparent layer is partially reflected at the upper as well as at the lower interface.
When the transmission method is used for measuring, emitter and detector are facing each other, with the measured material in between. Radiation is weakened by the measured object, and the degree of weakening is subject to the density, thickness and composition of the measured object.
Usually, Infrared sensors are offered as back-scattering sensors. Though if necessary, the construction as a transmission sensor is possible as well. Based on a patented measuring method, CONESPLIT® Same Spot Technology for direct (selective) online layer thickness measurement represents an advantage that sets BST ProControl apart from the competition.
The ultrasonic sensor utilizes the impulse echo method for thickness measurement. It sends out an ultrasonic impulse which is reflected by the measured object and then received again. The distance from the measured object to the sensor is specified by the runtime of the impulse.
This sensor is based on the triangulation measuring method. Here, a focused infrared-beam produces a spot of light on the measured material. The reflected part of the beam is recorded by a PSD/CCD-detector within the sensor and therefore enables the exact calculation of the distance to the object.
Isotope transmission measurement is a contact-free measuring method, measuring the basis weigth (g/m2). It uses the fact that all radiation is decreased when passing through materials.
The principle of optical triangulation is the basis for DELTA MASTER 3 sensors. It measures the material’s surface by projecting a fine measuring line upon it. A geometrically ultra-stable matrix CCD camera charts the visualization of this line and evaluates it on the basis of digital image processing methods.
The non-contact measurement principle bases on the precise definition of a linear fanned out laser beam. The thickness of the material causes the shading within the measuring area and a proportional influence of the receiver diode takes place. A distance measuring system compensates the distance changes between the sensor and the reference roller, whereupon the results are evaluated by a special digital signal processing technique which determines the exact material thickness.