Why Ethernet Can Be Your Best Connection

Ethernet, fieldbus, and PCI are the latest networks vying for dominance in the industrial motion-control arena. The winning technology will need industry support and confidence to ensure long-term viability. EDITED BY John R. Gyorki Compumotor's 6K4 controller connects to the Ethernet network for a wide variety of motion-control applications. For example, UniWest of Pasco, Wash., a leader in the nondestructive testing industry, upgraded from an ISA bus to the 6K4 controller with Ethernet connected to their three-axes scanners for inspecting jet engines. When the Ethernet controller resides outside the computer, the only connection needed is a Category-5 Ethernet cable. To add more control axes, use a readily available Ethernet hub or switch. Then, replacing a controller only involves configuring a new motion controller with software for the same, easy connection. Consider an Ethernet motion controller that sends and receives 512 bytes of information every 10 msec. On a 10-Mbits/sec network, this consumes only 4% of the network bandwidth, and on a 100-Mbits/sec network, it is less than 0.5%. Video teleconferencing, by comparison, easily transfers up to 40 kbytes every 10 msec, or 80 times as much data. This corresponds to 40% of the bandwidth of a 10-Mbits/sec network, and 4% of a 100-Mbits/sec network. In relation to video conferencing, it's easy to see that a motion controller consumes relatively little in terms of overall bandwidth. Therefore, in all but extreme data-sensitive applications, Ethernet and fieldbus are more than adequate. Hundreds of motion-control users have chosen Ethernet over fieldbus and PCI. But, as far as industrial motion control is concerned, all are capable of carrying the same information between a highlevel machine