Performance and Efficacy Scorecard Comparison

Performance and Efficacy Scorecard Comparison

Normally, there are countless technical dimensions of a standard that a customer/consumer must take into account when considering the adoption of a standard. All of these technical dimensions are really only significant if the fundamental performance delivered by the standards is nearly the same. But the performance of the standards varies widely, because the architectural differences render a wide performance difference.

Further, if a standard doesn’t compare from a price/performance standpoint, the standard will unlikely become viable in the long term. In other words, if the standard does in fact achieve the performance, but there is an expensive component that is required to achieve that result and that changes the economics, then that standard will not be viable either.

As noted at the top, the standards use three different mechanisms for network access and data synchronization, which we summarized below and now include the protocols:

OPEN SOFTWARE/STANDARD ETHERNET – Ethernet Powerlink

In Powerlink environments, a software-based master controls the timing on the network and the master authorizes individual nodes to send data. The benefits of this approach are that it still relies on the Ethernet standard and manipulates and controls latency by controlling who can access the network. Because it strictly relies on the Ethernet standard, it can never deliver the performance of standards that simply want to reuse the low cost hardware components (NIC cards, CAT5 cabling) and are willing to modify the Ethernet protocol – usually at the slave component level.

Typically, this means the servo drive or I/O vendor must include an ASIC in their solution that allows them to comply with the modified Ethernet protocol. And this becomes a barrier to adoption for the driver manufacturer. The larger the cost, the more the resistance to adopt the standard. As it turns out, PROFINET IRT is the most expensive approach for this category of fieldbus. SERCOS III’s moderate hardware requirements are next, and EtherCAT offers the least expensive hardware solution. In the end, Beckhoff’s choice to keep the Slave ASIC cost very low lowered the barrier to adoption and allowed EtherCAT to deliver the best price/ performance solution.

With that as background, the table below compares the real-time behavior of an application in which 100 axles need to be controlled synchronously. The two criteria analyzed in terms of performance measurement are the response time (cycle time) and the jitter (that is, the variation in response time).

Real-time comparison of the various real-time methods
(Source: IEBmedia)

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All five real-time methods are powerful in performance, with response times of less than or equal to one millisecond. Ethernet/IP, EPL, and PROFINET-IRT are similar in magnitude; SERCOS-III and EtherCAT are faster and more precise than the other three real-time methods by an order of magnitude.

Clearly, the top performing protocols - PROFINET IRT, SERCOS, and EtherCAT – benefited from having better hardware integration. PROFINET IRT requires substantial (expensive) switches and complex configuration effort to make it work. SERCOS depends on a hardware station, also expensive. The magic of EtherCAT is that Beckhoff charged a small, acceptable fee for the ASIC in the slave device and there were no other costs.

In conclusion, EtherCAT stands apart from a price/performance perspective. It offers the best performance, least jitter, and the lowest cost for incorporating the proprietary hardware required to deliver the determinism. As we will see in the next section, this creates the tipping point for market acceptance.

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