A closer look at ARCNET® technology reveals a protocol whose application
hasn't ended. ARCNET may not receive any name recognition, but one company
still employs its use to create the control system for gas turbines in
certain countries, especially since ARCNET has been an excellent network
technology throughout the years.
In the early days, the company's engineers desired to achieve increased fault tolerance in the system's triple modular redundant architecture. Triple modular redundancy uses two-out-three voting to allow for high reliability. The objective of triple modular redundancy is increased fault tolerance, enabling any single-point failure to be diagnosed and repaired while the system is online.
In order to attain increased fault tolerance, the engineers realized that the system called for a higher bandwidthnearly 2 Mbaud.
By utilizing synchronous computing frames, it required ARCNET bandwidth. "ARCNET can't be beat for its speed and bandwidth in this application," said one engineer. Although the default ARCNET speed is 2.5 Mbps, ARCNET can operate as high as 10 Mbps. Engineers chose to contact Contemporary Controls, Downers Grove, Illinois, who was the leader in this technology. "ARCNET's token-passing protocol technology is of particular significance for this system since timely responses and coordinated motion are required," said engineers. "This deterministic protocol enables the synchronization of all the system's controls in a predictable fashion. ARCNET's high-speed 2.5 data rate responds quickly to short messages which provides faster downloads."
To interface with the system's three controllers to the ARCNET local area network (LAN), an adapter would be inserted in each Human-Machine Interface (HMI) system. The engineers said the HMI unites all the displays and functions needed for real-time control and monitoring of turbo machinery methods, auxiliary apparatus, driven devices and process alarms associated with power plant control. For the company, Contemporary Controls developed an adapter that had a PCI interface which the HMI system required.
The PCI20U adapter with its performance enhancements was the solution. The PCI20U uses the 33 MHz PCI bus to reduce message handling time and improve data throughput. The engineers witnessed this as a good benefit for overall system efficiency. It incorporates the newer COM20020 ARCNET controller chip. New performance and integration enhancements include command chaining operation and an internal 2K x 8 RAM buffer.
Connection of the HMI PC to the control system's panel(s) is through Contemporary Controls' MODHUB-16 modular active hub via coaxial cable. This link ties all the control system's controllers and PCs together. In this application, copper grounding is essential because it reduces noise and improves control. Also, turbine generators can produce more than 20,000 Amp at high voltage so noise immunity from this is very important. Multimode fiber optic cabling and repeaters are implemented in order to accommodate longer distances between the operator-interface computer and the turbine control panel. Because of the hub design, the MODHUB-16 can have a coaxial or fiber interface to provide the most flexibility in cabling within a power plant. These 4-slot chassis hubs offer worry-free operation using low-power, low-heat CMOS components: high-efficiency LED lights; plus a special cooling system inherent in the design; and network diagnostic capability utilizing LED indicators. A universal power supply accommodates world-wide voltages and frequencies. Also, the MODHUB-16 is UL 60950 Listed, Safety of Information Technology Equipment. Engineers said, "We have a mandate that stresses strict quality standards because if a turbine fails, the downtime costs for our customers are immense."
According to the engineers, it is also important to note the valued work received from Contemporary Controls. "We would like to express our thanks to Contemporary Controls for their superior service, rock-solid delivery and consistent product supply," they explained. "With Contemporary Controls, we don't have to worry we know it will happen on time without a hiccup."