When it comes to Industrial Ethernet fieldbus protocols, it can quickly become confusing to understand how they work and what some of the differences are. We as engineers get excited about the latest and greatest hardware, but we must remember that behind the scenes is a communication network that is helping define the performance of that hardware. In order to better understand the impact that a communication network can have on an industrial control system, let’s speak a bit to Ethernet POWERLINK. POWERLINK is frequently employed by IFP Automation on systems as our standard when utilizing B&R hardware for optimal system performance.
What is the difference between standard Ethernet and Industrial Ethernet?
One of the major differences between standard Ethernet protocol (or TCP/IP) and Industrial Ethernet is collision avoidance. The data transfer in standard Ethernet may have irregular delays, which is unacceptable when trying to achieve hard real-time performance. In circumstances where irregular delays can be acceptable (office computers, printers, serving web pages, etc.), Ethernet TCP/IP is perfectly fine. But in industrial motion control applications, a solution for hard real time communication is needed.
Because of this, an Industrial Ethernet protocol must use preventative methods that avoid such collisions. The data transmission must also occur within a very specific window of time, which is referred to as jitter. Soft real-time performance can tolerate a limited amount of jitter and may have cycle times of up to several hundred milliseconds. Soft real-time performance could be used for applications such as temperature monitoring. Hard real-time performance on the other hand would be used for applications such as motion control, and commonly requires sub-one-millisecond cycle times. (more…)