Safety glass, solar cells, flat screens and smartphone displays are made up of several material layers. Measuring the exact thickness of individual layers in production is a physically complex process – a challenge for measurement technology. For quality inspection and process control of manufactured transparent multi-layer materials, Micro-Epsilon offers its confocal-chromatic displacement sensors with multi-peak feature. The confocal-chromatic measuring principle allows one-sided thickness measurement of these layers to micrometre accuracies. The confocalDT series of sensors can measure up to 5 layers by evaluating 6 measurement values on the boundary areas. To accurately determine the thickness of each layer, the controller retrieves the refractive index for each layer from the material database. Each refractive index is corrected depending on the wavelength: three refractive values are used for thickness calibration (beginning, end, middle of the layer).