TwinCAT performance in new dimensions through new generation of processors

Software PLC at blazing speeds

Beckhoff have succeeded in reducing the execution time of the TwinCAT, software based PLC system to below 1 µs, for the classic 1 k line IL code part. For Beckhoff this was not difficult since using the latest generation of processors and memory options. Therefore, TwinCAT performance is attributed to processors with ever higher clock rates and ever faster memory access. As you may surmise, the limit has yet to be reached.

Nevertheless, the question arises as to whether such performance reserves are really necessary for a particular application. The answer is simple: New options invariably open up new applications. Applications that previously required several CPUs are now concentrated on a single PC. Controllers that previously were equipped with decentralized intelligence are today dealt with cost-effectively through software on the PC. Utilizing the performance of the PCs, motion control applications that were regarded as impossible only a few years ago can also be realized in software. Not only the number of axes that can be position-controlled on a PC is increasing constantly; complex algorithms such as cam plates and synchronous movements can also be dealt with. There still remains PC control processing power for ergonomic visualizations.

Since there is not a standard PLC performance measurement test, Beckhoff explain their performance test. The Beckhoff performance test, for PLC systems includes averaging over 1000 randomly selected lines of IL code. These lines include load, memory and arithmetic operations. As data types, boolean and bit data types in a certain ratio are used and complemented with operations with REAL types. In order to eliminate caching effects in the PC, in addition several hundred thousand lines of code are calculated and subsequently averaged. This test is comparable with real PLC projects. Here too, we have a mixture of various commands and data types.

The results of this performance test are shown in the diagram. The test was carried out for the Beckhoff Embedded PC CX1000 with a Pentium I compatible CPU with 266 MHz. As pure PCs, Intel Pentium III with 850 MHz, Intel Celeron with 2.0 GHz and Intel Pentium 4 with 2.8 GHz were included in the test. As expected, the test showed particularly good results, if 32 bit integer or REAL data types were used. REAL operations were naturally calculated with the Floating Point Unit (FPU) of the processor.With an Intel Pentium 4, 3.0 GHz processor and still faster memory access, link times of less than 1 µs are possible under optimum conditions. Furthermore, the reduction in engineering costs through the reduction in the time required for programming and commissioning should not be underestimated. Increasing PC performance also leads to reduced turn-around times: Every programming/ compiling/testing process is shortened.

In the past, such gains in PC performance through new generations of processors and memory were frequently held up by the fieldbusses. Over recent years, there has been little movement in this area. Through the new Beckhoff EtherCAT system, a new, faster fieldbus enters the market, which meets the increased requirements and can keep up with the increased performance of PC-based control technology. A standard open Ethernet PCI master bus card allows DMA (direct memory access) and replaces the “slow” PCI bus fieldbus cards. The high Ethernet bandwidth of 100 Mbit enables the collection of a large number of data at very short cycle times.

The PC will thus be able to enter new automation regions, which previously could only be handled by very fast special hardware with special busses.With EtherCAT as a fieldbus, fast control technology and measurement tasks can now be realized with normal PCs.

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