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Modular design makes smart transducers plug-and-play possible.

As an increasing number of microcontrollers, sensors, and actuators are embedded in agricultural machines and processes, efficient system integration becomes a critical issue. A recently developed agricultural bus standard, ISO 11783, provided a platform for mobile equipment communications through controller area networks (CAN), enabling plug-and-play of microcontrollers of different makes, types, and models. However, plug-and-play installation of sensors and actuators remains an unsolved task.

Standardization efforts initiated by the National Institute of Standards and Technology led to the development of IEEE 1451.1-5, the standards for intelligent sensors and actuators, referred to as "smart transducers." The smart transducer interface module (STIM) provides up to 255 channels to accommodate sensors and actuators with signal conditioning and processing functions that are generic to each type of signal (analog, digital, pulse, etc.). The transducer electronic data sheet (TEDS) within the STIM stores information on specific transducers to allow self-identification, self-configuration, self-documentation, and self-calibration. The network capable application processor (NCAP) functions as a gateway between a network and the STIM. The transducer-independent interface (TII) provides a network-independent interface between the STIM and the NCAP. Recently, popularly accepted RS-232, RS-485, and USB serial communication protocols have been considered to replace TII.

The smart transducer concept separates the transducer interface from the network interface, hence, dividing the tasks between the transducer manufacturers and the system integrators (equipment manufacturers). While system integrators concentrate on networking of various sensors and actuators through transducer-independent NCAPs, transducer manufacturers can make their specific products generic through appropriate design of network-independent STIM and TEDS. By dividing the tasks, both parties can take advantages of their strengths while avoiding their weaknesses.

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Researchers at Kansas State University tested this new concept through the development of a weed-sensing and spray-control system. Among the two novel weed sensors embedded in the system, one used the conventional interface between the sensor and the CAN network, while the second one, designed using the "smart transducer" concept, contained two microcontrollers serving as STIM and NCAP, respectively.

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For the smart weed sensor, six light-reflection signals measured at selected wavelengths were acquired, conditioned, and processed in the STIM. The TEDS in the STIM contained a meta TEDS that describes the general information about the sensor, a channel TEDS that defines the individual channels, and a calibration TEDS that contains complete calibration data for each channel. The NCAP was designed specifically for CAN. The smart weed sensor worked well with other components on the CAN network, including a Fieldstar virtual terminal, a GPS, and spray nozzles. Extensive tests have shown that the weed detection rate was higher than 80 percent.

Experience obtained by KSU researchers demonstrated that the IEEE-1451 smart transducer standards can be integrated with agricultural bus standards to provide a flexible solution for system integration. The smart transducer concept extends the modular design approach from the CAN node level to the transducer level. At the CAN node level, microcontrollers made by different manufacturers can be "plugged" into a CAN bus that conforms to the ISO 11783 standard and immediately start to "play." At the transducer level, various types of sensors and actuators made by different manufacturers can be "plugged" into the CAN network through IEEE 1451-conforming smart transducer modules and start to "play." Thus, combined use of the IEEE-1451 and ISO-11783 standards may provide complete plug-and-play capabilities for sensors, actuators, and microcontrollers. As precision agriculture technology advances, modular design and plug-and-play capabilities have become a future trend that would be appreciated by sensor manufacturers, system integrators, as well as farmers.

ASABE members Naiqian Zhang, zhangn@ksu.edu, Jiantao Wei, Kansas State University, Manhattan, KS, USA, and Ning Wang, McGill University, Ste-Anne-de-Bellevue, QC, Canada
COPYRIGHT 2005 American Society of Agricultural Engineers
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Title Annotation:Focus on Automation Technology
Author:Zhang, Naiqian; Wei, Jiantao; Wang, Ning
Publication:Resource: Engineering & Technology for a Sustainable World
Date:Sep 1, 2005
Words:607
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