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SENSORS & DATA CONVERSION Fig. 3: Angle error using pre/post segmented linearization. earization allows for a sinusoidal-based compensation of the error signal, which helps remove the high harmonic error content in misaligned as well as side-shaft arrangements. The added performance from harmonic linearization comes at the cost of higher computation time: a situation known as “latency”. For many applications the additional latency will not be a problem. As an example, in typical electronic power steering (EPS) system hand-wheel angle sensor ICs, a new angle value is requested every 1ms, meaning that there is more than enough time to perform even 15 harmonics of linearization – see figure 5. In addition, many applications will make use of the ORATE (programmable output rate) feature of the sensor in order to reduce the noise-floor of the angle measurement by over-sampling. This will also provide enough time to perform linearization Fig. 6: Misalignment effects: (left) definition of X, Y and Z mapping axes; (right) misalignment performance (vertical and lateral axes) at air gap = 4 mm functions without added latency since the additional averaging will allow for more time to be budgeted for linearization operations. Effects of XYZ misalignment To assess the effects of mechanical misalignment of the linearized angle sensor IC, a mapping analysis has been carried out as shown in figure 6. The results show the dependence of angle error performance on magnet geometry. It was seen that a taller ring magnet translates into better tolerance to vertical misalignments, whereas a thicker ring magnet trans¬lates into better tolerance to changes in air-gap. Conclusion On-chip, programmable, and customisable linearization, as implemented in the A1332 angle sensor IC, allows the system designer to meet the aforementioned accuracy objectives without adding additional complexity and cost to the system design. While segmented linearization achieves faster processing times, it is limited in its ability to correct for sinusoidal error terms. In this regard, the harmonic linearization performs better. Moreover, the flexibil¬ity in the harmonic linearization approach, particularly the ability to change the number of correction harmonics used, allows the user to achieve the optimal trade-off between computation time and error performance. The result is that ±20 degrees of angle error can be brought to within ±0.3°when linearization is applied. Whatever the angle sensing challenges faced by the systemlevel designer, a combination of appropriate magnetic design and advanced on-chip linearization can help achieve the desired performance while minimising added complexity and cost. Fig. 5: Linearized angle error (left) and added angle latency (right) plotted against the number of harmonics applied. Enhancing sensor reliability through venting By Gary Chan As the Internet of Things continues to expand, it is estimated that by 2020 anywhere from 25 to 30 billion electronic devices will be connected wirelessly. The purpose of these devices is to exchange data with other connected devices or operators to perform tasks such as: • rotating solar panels to maximize access to sunshine or measuring humidity and soil moisture for commercial and farming irrigation systems; • increasing vehicle safety with active assist systems in automotive and heavy-duty equipment; • controlling a manufacturing process to ensure product quality or managing inventory availability; and even • creating Smart City networks for improving traffic flow, Gary Chan is Application Engineer at W. L. Gore & Associates - www.gore.com 40 Electronic Engineering Times Europe June 2015 www.electronics-eetimes.com


EETE JUN 2015
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