High resolution sensor ideal for measuring transparent or shiny surfaces

Citation

(2005), "High resolution sensor ideal for measuring transparent or shiny surfaces", Sensor Review, Vol. 25 No. 2. https://doi.org/10.1108/sr.2005.08725baf.003

High resolution sensor ideal for measuring transparent or shiny surfaces

High resolution sensor ideal for measuring transparent or shiny surfaces

Keywords: Sensors, Measurement

A confocal chromatic displacement sensor uses halogen light source for improved stability.

For manufacturing companies and design engineers who need to measure and monitor transparent or shiny surfaces such as polished metal and glass, Micro-Epsilon's new displacement sensor is able to measure independently from surface reflexion by using a unique “confocal chromatic” measurement principle. Surface contours can be measured accurately, as well as thicknesses of transparent materials, distances and hole depth. The sensor has a much higher resolution and is more stable than laser diode alternatives (see Figure 1).

Figure 1 Surface contours can be measured accurately as well as thicknesses

The Micro-Epsilon optoNCDT 2400 confocal chromatic sensor measurement system consists of a controller and a displacement sensor. A fibre optic cable, which can be made to almost any length to suit the application, connects the two components together, enabling the sensor to operate at a considerable distance from the controller.

The system works by focussing polychromatic white light onto the target surface using a multi-lens optical system. The lenses are arranged in such a way that the white light is dispersed into a monochromatic light by controlled chromatic deviation. A certain deviation is assigned to each wavelength by a factory calibration. Only the wavelength which is exactly focussed on the target surface or material is used for the measurement.

This light reflected from the target surface is then passed via a confocal aperture to the receiver, which detects and processes the spectral changes. This unique measuring principle enables displacements and distances to be measured very precisely.

Both diffuse and spectral surfaces can be measured and with transparent materials such as glass, a one-sided thickness measurement can be accomplished along with the distance measurement. The emitter and receiver are arranged in one axis, hence shadowing is avoided (see Plate 3).

Plate 3 System to measure light bulb wall thickness

According to Chris Jones, UK MD at Micro-Epsilon: “Typical applications for the sensor include the profile measurement of coins, glass thickness, surface measurement of halogen reflectors and light bulb thickness measurement. The sensor is also suitable for nanotechnology applications as it has a spot diameter of between 7 and 10μM, which is much smaller than the laser diode sensors. In addition, customers will be using a sensor with a halogen light source rather than a laser diode, so health and safety issues won't be a concern.” Measuring ranges are 0.08, 0.35, 1.0, 3.0, 10 and 24mm. Linearity is less than ± 0.03 per cent FSO. Resolution is 0.004 per cent FSO and measuring rates (selectable) are 30, 100, 300 and 1,000Hz.

For further details, contact Micro-Epsilon UK Ltd. E-mail: chris.jones@micro-epsilon.com