Networking Protocols (sidebar)

Dec. 1, 2004
Here’s a quick rundown of the major networking protocols used in automation systems for process and discrete manufacturing.

DeviceNet: ODVA (Open DeviceNet Vendors Association) is the user group that manages DeviceNet technology. DeviceNet is based on CIP (Common Industrial Protocol). Largely seen as an appropriate protocol for discrete manufacturing, DeviceNet was originally developed by Rockwell Automation Inc., of Milwaukee. DeviceNet is an application-layer protocol that uses Controller Area Network (CAN) technology originally developed by Bosch AG in Germany. CAN supports a single topology: a bus with drops. DeviceNet supports a wide range of device types, from photoelectric sensors to drives and mass flow devices. ODVA sells the DeviceNet conformance test software, and vendors and end users can purchase the software to test and pretest their devices.

Foundation Fieldbus: The Foundation Fieldbus networking protocol includes software and hardware specifications. Products from multiple vendors are designed to conform to this standard. Foundation Fieldbus is used primarily in process industries, and is suited to hazardous settings because its robust application layer allows for closed loop control and hard redundancies.

“The Foundation Fieldbus is not just a network,” explains Dave Glanzer, director of technology development for Fieldbus Foundation, the Austin, Texas-based organization that manages Foundation Fieldbus in North America. “There are standardized function blocks in the EDDL controls, and the Fieldbus Foundation distributes this information to the controls themselves.”

Hart Protocol: The Hart Field Communications Protocol is widely used in the industry as a standard for digitally enhanced 4-20 mA communication with smart field instruments, which are common in the process industries. A large number of suppliers manufacture products that use the Hart protocol. The Hart protocol was designed specifically for use with intelligent measurement and control instruments, by adding a digital signal that runs concurrent with the traditional 4-20mA analog signals.

Profibus: Profibus is a fieldbus and device network technology that began life in Europe, though it is making headway into the North American automation systems market. The protocol serves both process and discrete manufacturing. Profibus PA (process automation) allows sensors and actuators to be connected on one common bus line, even in intrinsically safe areas. Profibus DP (device protocol) is optimized for high speed and inexpensive, plug-and-play connectivity. It is designed for communication among control systems and distributed inputs/outputs (I/O) at the device level, typically in factory automation.

See the story that goes with this sidebar: Automation Networking: Stable Protcols and Changing Device Language