TypicaL Load Bank COmmunication Protocols
The application of network communication protocols depends on numerous variables such as the type of load test, load capacities, number of load banks, and the distance between load banks. Avtron load banks offer a variety of network communication protocols suited to the best load test application.
A Controller Area Network (CAN bus) allows machinery and devices to communicate with each other without the need for a host computer. CAN bus is a message based protocol often used in the military and automobile industry.
In terms of load banks, CAN bus is often used for lower capacity, non-permanent models. CAN bus offers a fast response time of approximately 250 kilobits per second (kbps), which is advantageous when many smaller portable units are networked together at distances less than 250 meters (820 ft). Load steps are applied instantaneously throughout the network to simulate real-life load stresses on various supplies. The multi-drop architecture of CAN bus allows for all the load banks in the network to receive messages at the same time. The multi-drop communication ability of CAN bus eliminates the need for unit to unit repeating which slows down response time. CAN offers a reliable network with low overhead for fast communication.
RS485 is multi-drop differential pair communications network. The multi-drop architecture allows for messages to pass in the network without the load banks being energized. RS485 networks operate at a lower speed (approximately 19.2 kbps) than CAN bus, but can communicate over distances of 1000 meters plus. RS485 is often used on higher capacity, permanently installed units, where fewer load banks require simultaneous control. The differential pair also promotes a strong signal with low noise. The setup of RS485 networks is fast and reliable with no need for preconfiguring of IP addresses.
Ethernet is one of the most common communication systems to network electrical devices with various communication protocols such as TCP/IP. TCP/IP provides separate IP addresses and the means of networking remote control and monitoring over vast distances through standard hardware such as routers or switches. Ethernet is limited to 100M (328 ft) per run until and a repeater is required to extend the distance. Most industrial facilities utilize Ethernet as a means of communication with the integrated Building Management System (BMS). Load banks are typically setup and controlled either manually or autonomously from a facility control room. BMS communication is usually via Modbus which is described below.
IP addresses are assigned to individual load banks or interfaced with gateway hardware to allow a load bank network to be much larger than a typical CAN bus or 485 network. The Ethernet network must be preconfigured ahead of time, which may result in additional setup time. Messages have much larger overheads, therefore real time communication is more difficult. As Ethernet grows into into the Gigabits per second, Real Time Ethernet is becoming more common.
Modbus is an industry standard communication protocol developed in 1979 by Modicon (now Schneider Electric). Modbus has a variety of protocol versions that can be used on various hardware communications systems such as RS485 or Ethernet. Modbus is useful when monitoring or controlling many devices. The main control point will read/write registers or address locations which makes Modbus a flexible protocol and easy to implement.
Load bank control over Modbus allows the user to better tie into their Building Management System and implement a load bank into their program.
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