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overall accuracy of print color detection based on the specific application setup. A white LED was chosen as standard light source. Via regression equation for spectral approximation it is possible to achieve average accuracies of ΔE00 = 0.25 for Fig. 6: Cyan print color sample prior to otimization at a value of ΔE00 = 1.47 Cyan. The initial values without optimization have been ΔE00 = 1.47 – see figures 5 & 6. Looking a multiple color measurement methods in various fields of applications, it is clear that there are multiple ways to provide accurate and reliable analysis options for many solutions. The long-term stability, high accuracy, and compact size of MAZeT’s patented JENCOLOR interference filter technology allows utilization in mobile devices or tight environments. The most important fact is to know what kind of detector needs to be utilized within the test setup and how the measurement shall be performed. Accuracies and output values SENSORS & DATA ACQUISITION in form of color coordinates or the spectral fingerprint define the application-specific outcome of the results and analysis methods. Choosing the right method (like emission, remission or transmission) is essential for an accurate evaluation of different substances or elements. For example fluids react differently than solid objects, reflection or fluorescence require an altered measurement approach. Furthermore all measurements confirmed the fact that color detection cannot be set equivalent to common physical variables such as voltage, pressure or density. Since the main variables of color change upon the arrangement of the observer, the object and light - it is essential to optimize and calibrate color measurement tasks to the specific application. Defined reference points or targets need to be set to compare the specific ΔE 00 of chromaticity coordinates within particular color spaces – see figure 7. All measurements demonstrated an accuracy increase through usage of intelligent optimization processes or algorithms. Fig. 7: Samples measurements and targets in the CIE1931 color space. Polarised light measures rotation angle By Christoph Hammerschmidt Rotation angle sensors help users determining the position of a moving body relative to an axis. Such sensors are used in thousands of applications in mechatronics, machine building, aviation and the automotive industry. A new type of rotation angle sensor combines high accuracy with flexible handling plus high adaptability to individual measurement tasks. In factories, conveyor belts transport production goods from one process station to the next one. For the handover from one conveyor to the next one to work it is necessary that the conveyors belts are positioned very exactly at a certain point. To determine the exact relative position of these belts, a rotation angle sensor is required. Also in automotive design, rotational angle sensors are indispensable - for instance in closed loop control systems that control the rotational speed of the drive shaft. Currently there are basically two types of rotation angle sensors available at the market: magnetic and optical sensors. Magnetic sensors offer very high robustness and resilience even in dirty environments. However, they are less accurate than optical sensors which in turn require a very exact installation. For this reason, optical sensors typically are difficult to handle and are not overly versatile. A new rotation angle sensor type, developed by the Fraunhofer Institute for Integrated Circuits (IIS), combines the strengths of both techniques. While it is an optical measurement system, it applies different functional principles than available products: The Fraunhofer researchers utilised the polarisation effect of light to measure the angle, explains section manager Norbert Weber. The researchers attached a polarising film to the object under test (e.g. a shaft) and directed a light beam to it. Only light that oscillates in a certain direction passes the film; if the shaft rotates, the polarisation vector rotates with it. This effect can be used for rotational direction indication. The reader module, implemented as an integrated circuit, is placed within the light beam that passes through the polariser. The surface of the chip bears a matrix of micro structures shaped as a grid. If the polarised light hits the grid the amount of light diffraction allows a conclusion to the angular position of the shaft. These grids - at least three are required - are attached to the sensor within the normal CMOS production process, at no significant additional effort. “Depending on the measurement task, we can add more grids to adapt the sensor to specific customer requirements or to increase measurement accuracy”, Weber says. With this design, the Fraunhofer researchers do not reach the exactness of optical sensors to 100%, but this array is much more robust and can be positioned flexibly. “The sensor does not even need to be placed exactly within the optical axis”, Weber explains. “All that counts is that it is hit by the light beam”. Even imbalances of the shaft do not affect measurement accuracy as long as the sensor is within the beam. 42 Electronic Engineering Times Europe June 2014 www.electronics-eetimes.com


EETE JUN 2014
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