Diagnostic capabilities accelerated with DeviceNet and PC Control
BUS OF THE MONTH: DeviceNet
ew smart technologies that will make us the leader in low cost production, while giving a greater amount of control.'
Synergies Impact Diagnostics
er, allowed access to the diagnostics they needed to run their plants efficiently. The DeviceNet communication protocol is based on a broadcast-oriented, communications chip--the Controller Area Network (CAN) chip. The CAN chip provides reliable real-time communication at a low cost. Expensive, complex wire harnesses, used in traditional two wire field I/O, are replaced with a single twisted pair of wires.
I/O. The network cable is attached to the PC through a scanner card enabling the PC to increase system control through the ability to share data over one cable.
Diagnostics At Work
..At the Ford installation, production operator Paul Arendash has used the system diagnostics to help electricians troubleshoot a problem with a limit switch. While modifications were being made to the new system, Ford activated the old control system. During that time, the production line experienced a problem.
t part is causing the problem and where it is. Then, I can tell the electrician and he can make an adjustment or replacement in an instant.' The new control system pinpointed the problems quickly and accurately. Additionally, engineering, production and maintenance personnel responded positively tothe new system's ability to identify and locate problems.
m diagnostics. It has provided usable information from smart devices, reduced commissioning time, and has been well received by skilled trade and operator personnel.
DeviceNet: An overview
..DeviceNet is a low-cost communications link to connect industrial services (limit switches, photoelectric sensors, valve manifolds, motor starters, process sensors) to a network. DeviceNet eliminates expensive hardwiring and has important device-level diagnostics not easily accessible or available through hardwired I/O interfaces.
Why the DeviceNet Communication Link?
..DeviceNet allows for the interchangeability of simple devices while making interconnectivity of more complex devices possible. In addition to reading the state of discrete devices, DeviceNet provides the capability to report temperatures, read the load current in a motor starter, change the deceleration rate of drives, or to count the number of packages that have passed on a conveyor for a specified period of time. Because DeviceNet is based on producer/consumer technology rather than source/destination, there are three I/O data exchange methods; polling, change-of-state (COS), and cyclic data production. These methods provide DeviceNet users with the option of configuring devices to produce data only when changes occur, or at pre-determined intervals, thus reducing traffic on the network and contributing significantly to increased systemperformance.
CAN Lowers Cost
..The DeviceNet communications link is based on a broadcast-oriented, communications protocol--the Controller Area Network (CAN). Consumer and commercial demand for CANis the key driver in lowering the price and increasing the performance of CAN chips. The chips for DeviceNet aretypically 5-10 times cheaper than chips from other networks.
DeviceNet at a glance
Peer-to-Peer, Multimaster, or Master/Slave
Based on Producer/Consumer Technology
Installed base has increased by over 50% each quarter.
Ability to remove and replace network devices under full power
Trigger mechanisms gives DeviceNet users more options
..Rockwell Automation/Allen-Bradley (Milwaukee, Wis.) has announced the availability of products embedded with change-of-state and cyclic data production technology for use with the DeviceNet network. This technology provides DeviceNet users with the option of producing data only when changes occur, or at pre-determined intervals in order to reduce traffic on the network.
s. This flexibility can contribute significantly to increased system performance over the DeviceNet network.
stock of data for operator interfaces and produce it at 1/2 second intervals, thereby preserving bandwidth on the network for nodes with rapidly changing I/O.
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