Industrial Ethernet Guide - The Dependence On Intelligent Nodes
The following is part of A Comprehensible Guide to Industrial Ethernet by Wilfried Voss.
In review, any Fieldbus system (a.k.a. Distributed Control), utilizing a certain level of network management, is based on communication between one central system (Master, Server) and several nodes (Slave, Client). These nodes are nothing else but processor systems, and old technology wisdom states that an increasing number of processors results in a performance boost of the overall system.
Distributed control also translates into “distributed intelligence.” In this case, "Intelligence" represents the nodes’ capability to accomplish a significant part of their control tasks without support from the central control system. The more these nodes process internally, the less they depend on the speed of their communication means.
This circumstance is vital for slower networking technologies (e.g., CANopen and DeviceNet) when it comes to high-performance requirements such as high-speed, high-precision motion control. Even with a slower data rate of 1 Mbit/sec (compared to Ethernet’s 100/1000 Mbit/sec) and less-than-perfect bandwidth, CANopen and DeviceNet are quite capable of handling complex most motion control applications. They accomplish this by reducing the communication traffic between Master and Slaves, including direct Slave-to-Slave communication. Naturally, there are limits.
The dependence on “intelligent” nodes, however, does virtually not apply to Industrial Ethernet due to its vast speed in combination with larger data packages. Industrial Ethernet also provides enhanced support for synchronizing nodes, an important factor for real-time control.
Industrial Ethernet applications still include “intelligent” devices, specifically motion controllers, but it does not rely on, for instance, high-performance digital I/O boards. This independence on intelligent control devices simplifies many design aspects for industrial applications.
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