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Sensors Shrink & Communicate without Wires or Batteries
Expo in Illinois showcases these sensors and more
Randy Frank, Contributing Editor -- Design News, August 13, 2007
Sensors Expo papers, booth displays and product announcements seemed to fall into three major categories — wireless, microelectromechanical systems (MEMS) or energy harvesting technology, and sometimes, all three. Applications such as automotive tire pressure monitoring systems drive perhaps the highest volume requirements and aerospace or deep space exploration implementations, such as those described in keynote presentations by Steve Squyres from Cornell University about the Mars rover or Gregory W. Withee from the Office of the Administrator of National Oceanic and Atmospheric Administration about the Global Earth Observing System of System provide the more exotic. Here is a representative example for each of these three hot technologies.
Microgenerator Eliminates Batteries
Perpetuum demonstrated its energy harvesting PMG17 microgenerator that uses vibration energy from moving equipment to eliminate batteries in industrial applications. Converting the vibration of equipment running on power lines operating at 50 or 60 Hz frequency into electrical energy, the microgenerator generates sufficient energy to power a wireless transmitter sending up to 6 kbytes of condition monitoring data every few minutes, or smaller amounts of data, several times a sec. While eliminating batteries, this approach also avoids expensive wiring. The unit harvests the twice-line-frequency vibration and with as little as 25 mg (RMS) vibration within a 2-Hz bandwidth, always produces a minimum power of 0.5 mW.
Hardware Location Engine Targets ZigBee Apps
The CC2431, a new System-on-a-Chip (SoC) from Texas Instruments’ Chipcon product line, uses a received signal strength indicator (RSSI)-based location engine to determine a CC2430 wireless node’s position. Known locations transmitted to a collector, such as a computer, PDA or handset, reduces network traffic and communication delays compared to centralized location systems. An accuracy of 3 to 5m can be achieved in typical applications. Supported by TI’s Z-Stack protocol stack, which is available for free downloading, the SoC targets applications such as asset and equipment tracking, inventory control, patient monitoring, remote controls, security and commissioning networks.
Mems Technology Shrinks Gyro
Micromachined from pure crystalline quartz, the double-ended tuning fork inside Systron Donner Automotive’s MicroGyro provides rate- sensing precision and can withstand temperatures up to 125C, making underhood mounting possible. The unit has a range of ±300 degree/sec, resolution of 0.025 degree/sec per least significant bit (LSB) and only 0.25 degree/sec RMS noise (at 35 Hz bandwidth), making it ideal for automotive electronic stability control applications. Unlike sensors that test at specific intervals and interrupt the sensor measurement to do so, the MicroGyro continually tests and measures its status and simultaneously senses angular rate, even during conditions of extreme temperature or strong g-loading.
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