Sensor combines gyrometer and accelerometer for electronic stabilizing systems - Embedded.com

Sensor combines gyrometer and accelerometer for electronic stabilizing systems

SensorDynamics announced the launch of the micromechanical combisensor SD755 for the automotive integrating gyrometer and accelerometer in one single package. Both sensors transmit their signals over a shared SPI interface that facilitates further processing as well as minimize development time and system costs.

With its product, the company aims at satisfying the demand for AEC-Q100 certifiable integrated sensors including monitoring circuitry that make them fail-safe at chip and module level. Also, minimizing the number of devices translates to system cost reduction. According to the vendor, SD755 is suited for applications for electronic stabilizing systems in cars that match the actual road curvature with the angle lock. When there is a difference detected, single wheels are systematically slowed down to avoid skidding. SD755 is suitable for all security related automotive or industrial applications to ensure a high degree of fail-safety. Furthermore, its features include mechanical robustness, a wide range for temperature tolerance and high stability in the long term.The SD755 is in response to high safety standards, especially in the automobile sector. All design measures involved in achieving this are to IEC 61508 standard and are a result of thorough FMEAs of the entire system consisting of gyroscope, accelerometer and circuitry. A particular circuit for monitoring both sensor elements and the signal conditioning path is integrated and alerts if a parameter goes out of defined limits. More than 40 parameters are monitored to ensure that it is fail-safe. Failure of any part of the combisensor is communicated to the superordinate microcontroller on an SPI interface plus an additional hard-wired line. Via SPI a detailed failure analysis can be accomplished in order to identify the source of error. The sensor is also able to monitor the microcontroller by means of SPI. If the latter should fail, the sensor may cut out the entire module. On the strength of this design, the SD755 achieves SIL 2 at component level and SIL 3 at system level.

An operating temperature range of up to 125°C makes the SD755 extremely flexible in terms of placement. It can be installed in the passenger compartment of a vehicle or under the hood. The SD755's gyroscope has two measurement rages implemented with full scale values between +/-10°/s und +/-500°/s. They are calibrated individually and set by default to +/-100°/s und +/-300°/s. The readings of both ranges are available simultaneously via SPI. Also the accelerometer has implemented two measurement ranges with full scale values between +/-1g und +/-50g. By default they are calibrated to +/-2g und +/-5g. Another important feature of the SD755 is the extremely fast recovery of the gyroscope after impact. This is only 5 milliseconds after a 50 g shock.The SD755 is especially suitable for automotive applications for reliable identification of dangerous situations as sliding or rollover.

Stability control systems help to prevent a vehicle from sliding; here the gyroscope detects the rotation around the yaw axis. Also the vehicle's transversal acceleration is measured with an additional sensor in order to provide information of road adhesion. For this application the SD755 offers the ideal combination of measurement axes and ranges for direct mounting on a PCB in upright position.

For rollover detection the rotation around the vehicle's longitudinal axis as well as the acceleration along the normal or transversal axis must be measured. Also for this application the SD755 is best suited.

Due to its failsafe feature the SD755 can also be recommended for stabilizing platforms or for positioning tasks in safety relevant applications. Examples are the positioning of industry robots or surgery robots. Three perpendicular assembled SD755 are forming an entire (IMU – inertial measurement unit) that measures acceleration und rotation along all three special axes. The second-generation sensor element is manufactured at the automotive-certified SensorDynamics site for MEMS sensors in Itzehoe in Northern Germany. The ASIC that forms part of the SD755 comes from the semiconductor fab of ST Microelectronics. The two components are OC24 packaged and tested by ASE in Korea.The SD755 is available now. Pricing is about 38 US$ at a quantity of 1,000 units/year. Evaluation boards are available upon customer request.

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