Agriculture Reference
In-Depth Information
sensing techniques are reaching maturity for major crops of wheat and other grains,
cotton, potato, sugar beets, beans, rice, and some specialty crops.
13.3.2 N
ETWORKING
T
ECHNOLOGY
In recent years, an increasing number of electronic control units (ECUs) with vari-
ous types of sensors and actuators have been embedded in agricultural machines
and processes. For example, a modern John Deere 8000 series tractor has at least 16
ECUs onboard (Deere & Company, 2001). To share information among the ECUs,
networking becomes necessary and feasible. Wired and wireless communications
have been used in many systems.
13.3.2.1 Controller Area Network
The Controller Area Network (CAN) was originally designed for networking among
embedded microcontroller systems in automobiles. Since its inception, CAN has
found many applications in industrial control, such as production line control, pack-
aging machinery, and milking machines, mainly because of its robustness, simplicity,
and reliability. CAN is a high-integrity serial data communications bus for real-time
control. It operates at data rates of up to 1 Mbps and has excellent error detection and
confinement capabilities. Many of the world's leading chip manufacturers now offer
a wide range of semiconductor devices that implement the CAN protocol in small,
low-cost controllers and interface devices. Many higher-layer CAN protocols have
also been developed to help simplify CAN system design.
Based on the CAN protocol, ISO 11783 is a bus standard for communications
protocol dedicated to agricultural equipment. This standard defines the requirement
for electronic communications between tractor and implements, between compo-
nents within tractors, within implements, and within other self-propelled agricul-
tural machines (Stone et al., 1999). The standard also provides supports for precision
farming applications. In ISO 11783, the detailed requirements for agricultural elec-
tronics communications, such as message types, identifier assignment, and network
management, are defined to enable a plug-and-play capability for ECUs made by
different manufacturers.
In recent years, the advancement of silicon manufacturing technology makes it
fairly cheap to integrate a microprocessor with physical sensors/controllers/actua-
tors and associated signal conditioning/processing circuits to form a single, com-
pact package—named “smart transducer/controller/actuator” (Johnson, 1997). The
“smart transducer/controllers” include signal conditioning and preprocessing capa-
bility while maintaining the original measurement and control functions. They can
easily implement “plug-and-play” in a target system and directly output processed
digital signals such that, with good electronic system designs, data corruption due
to noise pickup should not occur. Furthermore, smart transducers can be easily net-
worked; thus, operations of the sensing elements can be monitored via a network,
and diagnosis at the system level can be simplified (Wynn, 2000). The IEEE 1451
standards is a family of Smart Transducer Interface Standards that describes a set
of open, common, network-independent communication interfaces for connecting
transducers (sensors or actuators) to microprocessors, instrumentation systems, and
