Performance Analysis of Industrial Communications Devices and their Associated Protocols

How much faster is PROFIBUS than Modbus? What are the performance characteristics of one over the other? Many of the common communications devices and protocols used for industrial systems do not have quantitative measurements or comparisons published in the public domain. These protocols are commonly used in real-time control systems and process control systems using Programmable Logic Controllers (PLCs) as part of the collection of information from remote devices. Many of these devices can vary from proximity sensors and limit switches to bar code scanners and other PLCs. One of the most important attributes that these systems require is called determinism. The definition for determinism from the Merriam-Webster dictionary [1] is: 1 a: a theory or doctrine that acts of the will, occurrences in nature, or social or psychological phenomena are causally determined by preceding events or natural laws b : a belief in predestination 2 : the quality or state of being determined For many engineers, this means that the equipment they design will have predicable responses and results from the PLCs and other types of controllers used for industrial equipment and systems. System engineers and developers of industrial and military equipment generally do not, but should, perform this type of analysis for their equipment. Most of the common comparisons are only based on the bandwidth of the transport media, such as 10 Megabit Ethernet or 100 Megabit Ethernet. These comparisons do not take the protocols or the volume of data into consideration. Most system engineers and developers select devices and protocols based on simply the raw bandwidth of the media, rather than taking the overhead of the protocols and hardware latencies into consideration..