Token Passing Protocol Helps Refinery Increase Production
BUS OF THE MONTH:ARCNet
By Control Engineering Staff
The Flying J Oil Co. (Brigham City, Ut.) bought its refinery in North Salt Lake City in 1986. The refinery takes crude oil, natural gas, liquids, and other raw materials from its fields and processes them into gasoline, diesel fuel, propane, jet fuel, and specialty wax. Its capacity is 25,000 barrels per day; comparable in capacity with about 60% of the world's refineries.
The company recognized its need for automation in 1992, as diesel desulfurization equipment was required to increase the output of diesel fuel at the refinery. At the same time, Flying J decided to upgrade the refinery's existing manual control system. The company looked at a common solution, a distributed control system (DCS), but the DCSs examined were too much system for the refinery's production capabilities and weren't scalable. It was also high priced, proprietary, and required full-time support personnel.
Flying J went back to the drawing board, and decided to use PC-based control automation equipment to run its process control environment. The solution? ARCNet fieldbus technology coupled with Opto 22 (Temecula, Calif.) equipment.
rocessor that communicates over ARCNet to four computers. Another unit, the Hydro Diesel Desulfurization unit is controlled by two Mistic processors communicating over ARCNet with three computers, all through coaxial cable.
'We had a temperature loop that was operator-controlled, with a variance of 20 degrees Fahrenheit,' said Mr. Judkins. 'With computerized control and ARCNet technology, the variance is now only two to three degrees.' Consistency makes the company's equipment and catalysts last longer. Flying J has more on-spec product.
wn. ARCNet has a 'traffic light' that keeps communication controlled and organized data can always get through.'
ARCNet Controller for LANs
Manchester, N.H.-- Teletrol Systems offers a standard 2.5 Mb ARCNet LAN option for its Integrator building automation system. ARCNet is available for its Integrator 486, 186, and CS controllers as well as the AHC 186 controller. ARCNet is available directly in the system-level controllers. Teletrol's ARCNet media options include twisted pair, coax, and fiber-optic cable. ARCNet is used in all controllers, not just as a link between a workstation and one or two master units.
Teletrol Systems Inc.
Interface ModuleWorks with QNX 4.23
Downers Grove, Ill.-- The PC10466 Series of ARCNet network interface modules links PC/104 compatible computers with the ARCNet fieldbus. This series of modules incorporates the 16-bit COM90C66 ARCNet controller chip with enhanced features over earlier generation ARCNet chips. To utilize the expanded features of the COM90C66, an enhanced software driver is required. QNX has ported version 4.2 over to a 32-bit operating system kernel and has released it as QNX 4.23. The driver support for the PC10466 PC card has also been ported to the new system.
ARCNet Circuit Board Links Terminals
Columbus, O.-- An optional circuit board permits Mettler-Toledo Inc.'s Jaguar scale terminals to become part of Allen-Bradley's Remote I/O network. Made by Mettler-Toledo, the board is available as a factory option or a field upgrade. The board forms the interface with the Remote I/O network, making the Jaguar terminal virtually identical to Allen-Bradley products. Up to four clustered scales can operate through a single Allen-Bradley circuit board. The four scales--one or two per terminal--communicate over the ARCNet network used by the Jaguar terminals, then interface with the Allen-Bradley Remote I/O through the board.
Drive's Card Uses ARCNet
Rockford, Ill.-- Pacific Scientific's SC900 DSP-based brushless servo drives, with 7.5 to 60 A peak and 3.75 to 30 A continuous power levels, feature removable option cards for flexibility. One of these option cards, the OC950,adds stand-alone programmable position control to the servo drive. The OC950 can be ordered with Pacific Scientific's PacLAN interface. PacLAN uses a standard ARCNet token passing network .
ARCNet: A Brief Overview
ARCNet (Attached Resource Computer Network) is a controller-level fieldbus network that provides the physical and data-link layers of the International Organization of Standards OSI (Open Systems Interconnect) Reference Model. That is, ARCNet provides for the successful transmission and reception of data packets between two network nodes. A node refers to an ARCNet controller chip and cable transceiver connected to the network.
networks. Additionally, the worst time for receiving a token can be calculated, an important feature for real-time systems. Finally, the ARCNet protocol 'knows' when nodes are added to or disconnected from the network. The system automatically reconfigures the network without software intervention.
rk. Node addresses range from 0 to 255 with 0 reserved for broadcast messages.
y in quality standardized ARCNet equipment. The Standards Committee is currently revising the 878.1 standard to include the higher data rates. The ATA also provides information and support for members says, George Beason, executive director.
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