CHRomatic Confocal Principle for Thickness Measurements (transparent, up to 37mm)
The chromatic confocal measuring technique uses light from a variety of sources (halogen, LED, xenon etc) coupled into an optical fibre and delivered from the control unit to the optical probe via the fibre. With no moving parts or electronics, the optical probe comprises a series of lenses that exploit a feature of optics – axial chromatic aberration. The optical probe uses the chromatic aberration in such a way that each wavelength is focused at a different distance from the optical probe with blue closest and red furthest away and a colour continuum between.
The distance from the blue focus to the red focus is the measuring range of the optical probe. A surface within the measuring range will cause light of a wavelength determined by its distance from the optical probe to be reflected back into the optical probe, transmitted back to the control unit and analysed with a spectrometer. The wavelength measured by the spectrometer is then translated into a z-axis distance – the distance from the optical probe. The term chromatic confocal is used as judicious use of spatial filters mean that only reflections of light originating along the optical axis will be focussed onto the input aperture of the spectrometer. Reflections from regions other than the optical axis will be focussed either before or after the input aperture and will therefore not be analysed.
In the case of glass or transparent materials within the measuring range, light of different wavelengths (colour) will be reflected from both the first and second surfaces of the container, resulting in two signals being observed by the spectrometer. The wavelength difference (distance) between these two signals corresponds to the thickness of the material. The overall measuring range is used to name the optical probes; for example, the 12mm probe has a separation between the blue and red focus of 12mm in air, which corresponds to a maximum thickness measurement of approximately 18mm in glass (air distance x refractive index).
With reference to the analysis of the return signal, Precitec Optronik has developed a range of highly sensitive control units resulting in the accurate analysis of the wavelength signals. The width of the signals greatly affects the resolution with which a thickness measurement can be determined but high quality optics and a precisely configured sensor combine to achieve sub-micron resolution even at high speeds.
- Halogen, Xenon and LED sources available
- Thickness range from 20µm to 37mm
- Color and temperature independent
- Measurement rates up to 66kHz
- Easy to integrate inline or with other sensors
- Multi-channel systems available
- CHRocodile 2 S
- CHRocodile 2 SE
If you have an application that you feel might benefit from using non-contact chromatic confocal measurement and would like to discuss it in more detail please either contact us at +44 (0) 1604 654 220 or click through to our contact form and we'll be in touch as soon as we can.