MEMS, wireless techniques, standards provide sensing solutions
The second Sensors Applications Symposium (SAS), organized and sponsored by the IEEE Instrumentation and Measurement Society, addressed a variety of sensing applications from health care to homeland security and events in everyday life. In some cases, existing sensing technologies, including microelectromechanical systems (MEMS) sensors, were used and algorithms provided a new technique. However, in other cases, researchers developed the sensor specifically to meet the requirements of the application. The use of established standards, such as the IEEE 1451 for smart sensors and the Digital Addressable Lighting Interface (DALI), provided a foundation for several development efforts. Three applications provide a flavor for the symposium.
Adding Sensors to a Lighting Bus
In the paper “A Sensor Network for Buildings Based on the DALI Bus” researchers modified a lighting protocol to avoid establishing separate networks for lighting, HVAC, alarm and environmental monitoring systems in the same building. Developed specifically for lighting control, the DALI protocol is used for dimming, scene selection and detecting faulty light sources. Operating in the master-slave mode, one master controller in the DALI system can control up to 64 DALI slave units. Using the characteristics of the hardware interface, researchers modified the master to convert data into the format of the Transducer Electronic Data Sheet (TEDS) to be compatible with IEEE 1451.0. The enhanced DALI network protocol was successfully tested with a -20 to 100C temperature sensor, an illumination sensor and standard lighting devices.
Accurately Sensing Coins in Vending Machines
Commonly used sensing techniques for discriminating between coins in a vending machine include optical, electromagnetic, acoustic and impact sensors as noted in “Sensing in Coin Discriminators.” Using low-cost digital signal processing technology, a specially developed mechanism and all four sensing techniques, researchers developed a highly accurate means of detecting legitimate coins from counterfeits. A very low-cost accelerometer typically used for hard disk protection from Murata's PKGS family, a biomorph piezoelectric sensor, provided the shock input. The signals from the different sensors were acquired and processed in somewhat of an overlapping manner. Even though two sensors were located close to each other, the low correlation between the impact and acoustic signals from the accelerometer and microphone validated the need for several sensors to provide accurate detection.
Pedestrian Navigation System
In “Adaptive Step Length Estimation Algorithm Using Low-Cost MEMS Inertial Sensors,” researchers showed that the walking status of a subject could be measured in both indoor and outdoor environments even though step length varies considerably with the subject's speed and status. Using an Inertial Measurement Unit (IMU) from Microinfinity, the MI-A3330LS-U, and a Bluetooth module, an adaptive algorithm performs different linear fits to recognize the movement status such as walking or running. The MEMS device consisted of an accelerometer and a gyroscope. The technique could be applied to personal health care monitors to calculate the energy expenditure of pedestrians.
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