Gyro works in harsh conditions, simplifies installation

  • 19-Sep-2011 11:51 EDT

ADI’s gyro improves safety while trimming installation costs.

As active safety becomes a more important feature for mainstream car buyers, gyroscopes are seeing broader usage. Analog Devices Inc. aims to reduce manufacturing costs for sensor modules with a patented differential quad-beam architecture that also provides self-calibration and low power consumption.

The ADXRS800 iMEMS gyroscope employs multibeam architecture to minimize the influence of linear shock and vibration. The architecture uses one beam to monitor resonant frequency vibrations that can be filtered out so the other gyro beams can be focused on changes that occur during skids or rollovers. That makes it possible to put the part under the hood near the engine, where it can be close to the automatic braking system that works closely with electronic stability control sensors. Putting the gyro near the ABS controls can improve performance for active safety systems such as electronic stability control.

“When control units are under the hood near the engine, there’s a lot of vibration when all the valves are active,” said Christoph Wagner, MEMS Field Applications Engineer at ADI.

The ability to filter out noise can also help in conventional in-cabin sensor modules. “When the sensors are in the cluster next to the driver, when you’re driving on rough roads, or when a stone hits the bottom of the car, it creates a lot of shock that can affect the gyro,” Wagner added.

The gyro also operates at low current—6 mA under typical conditions. This is beneficial when the sensor is mounted in a module that includes the airbag’s accelerometer. The airbag sensors require some energy storage so they can operate if battery power becomes unavailable during a crash.

“The airbag has to respond for two seconds, so you need to provide a lot of capacitors or another energy reservoir. It makes a huge difference if you add a 6-mA part versus a 20-mA device,” Wagner said

He also noted that the gyro's use can help trim manufacturing costs. Unlike most competitors, it uses standard semiconductor packages that can be installed using standard pick-and-place processes.

“Other gyros require bumpers or tooling for mechanically isolated positioning,” Wagner said. “Our part also eliminates the need for rubber in the package. Rubber isn’t expensive, but the logistics of mounting it adds significant costs.”

The device also eliminates the calibration that’s typically required with sensors. This calibration usually occurs at the end of manufacturing, after the sensor module undergoes the stresses associated with solder baths and the vibration that occurs when modules are mounted. The ADI part is self-calibrating, eliminating the need for manual tuning.

“In the past, Tier 2s had to do the calibration, storing data that would compensate over the automotive temperature range,” Wagner said. “We store that data on this chip and provide compensation over the full temperature range, going up to 125ºC for under-hood applications.”

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