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Mouser Electronics White Paper The sensor can also be used in intelligent seatbelt retractors. When the sensor is mounted opposite a dipole magnet on the end of the seatbelt retractor spool shaft, the sensor can count rotary turns of the shaft to measure belt extension for occupant classification (Figure 17). Because an occupant typically extends and fastens the seatbelt before the ignition is turned on, this uses the sensor's ability to track and retain position information while power is off, enabling a post-power-on reading of seatbelt extension. When the vehicle is turned on, the seatbelt retractor electronics can read the extension and retraction information and program appropriate airbag deployment strategies based on the occupant's size and closeness to the airbag. In addition to providing occupant classification when the vehicle turns on, the system can provide continuous dynamic position monitoring of the occupant (indicated by the yellow arrow in Figure 17) and modify the airbag deployment strategy accordingly. System-Level Advantages Sensors that employ AMR and GMR technology for angle measurement and turn counting offer a variety of system-level benefits by eliminating the need for mechanical parts and backup batteries. They enable compact, reliable system solutions that free up space in robots, autonomous vehicles, and other equipment, making room for additional mission-critical functionality. They simplify designs by incorporating multiple functions, including signal conditioning, communications interfacing, and angle- and turn-count capabilities. This enables smaller, lighter systems with fewer parts while supporting direct digital interfaces to reduce controller complexity and increase scalability to high-volume production. By providing true power-on position information, the ADMT4000 sensors enable faster recovery with no system downtime for rehoming and recalibration. These sensors also provide high reliability in industrial applications. The sensing mechanisms are not subject to mechanical wear from gears, which eliminates the need for scheduled mechanical maintenance or complex predictive maintenance strategies that continually monitor moving parts for vibration signatures indicating imminent failures. In addition, the sensors' ability to retain power- off position information eliminates the need to replace batteries or maintain rechargeable batteries. For automotive applications, these sensors offer enhanced robustness with automotive-qualified temperature ranges and diagnostic capabilities. Additionally, dual redundant systems will provide sufficient reliability to achieve the appropriate Automotive Safety Integrity Level (ASIL) as defined in the ISO 26262 standard for road vehicle functional safety. Figure 17: Seatbelt retractor application of ADMT4000 multiturn position sensors. (Source: Analog Devices) Looking Ahead With ADMT4000 multiturn sensors, contactless, power-off-resilient multiturn sensing is now cost-effective, reliable, practical, and compact, leading to advancements in numerous applications. For automotive applications, dual-redundant systems will reach ASIL D levels of functional safety. Furthermore, these position- tracking devices will be increasingly used in applications such as modular robotics, exoskeleton joints, medical equipment, and smart industrial automation—in short, any application that requires rotational turn counting and angle sensing.

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