Thread Content
Rockwell’s NetLinx provides seamless routing of data from the shop floor level to the Ethernet-based enterprise level, without the need for programming or gateways. Siemens needs to use gateway controllers to connect different networks, and for data transfer from proprietary Ethernet to Profibus, to ASI, and to field devices, message programming that is quite complex is required on each controller. With NetLinx, users no longer need to program in order to transfer data between different networks. This eliminates the issue of memory address mapping, and there is no need to worry about data types. The producer/client model is the latest network technology that allows for flexible adjustment of the network to meet stringent control response requirements, thereby providing systems that are more responsive, flexible, and efficient. When the application requires it, proactively provide I/O and processor status events to where they are needed. This is achieved through variable-rate reporting, I/O sharing, scheduling, periodic methods (time-based), etc. Profibus was designed in the 1980s; constrained by the master/slave model, all slave devices use a polling method. The response time of the Profibus system increases as more devices are added; if the system’s response speed is not acceptable, there is no flexibility in adjusting the network. The I/O modules of Profibus must wait for polling by the master controller; sharing of I/O status can only be achieved between processors through user programming, and this usually requires different proprietary \"peer-to-peer\" networks (Ethernet, FMS, or Siemens \"MPI\"). ControlNet provides both real-time control to I/O and factory equipment, as well as messaging to peer devices or smart devices. The Profibus solution typically requires an additional network, such as Ethernet or Siemens’ proprietary “MPI” network, for peer-to-peer communication; this entails more connections, more communication devices, and higher costs. The Profibus messaging capability is limited. Various different networks: DP, PA, FMS (and other networks), each with its own proprietary version from Siemens “Sinec”. “The “Sinec” device is not compatible with the latest network version. ControlNet can maintain reproducible responses, independent of network device messaging, programming, or even the addition of nodes. ControlNet’s speed is independent of the number of nodes, the medium, and the repeaters. The speed of Profibus is related to the number of nodes, the medium used, and the repeaters. Only through fiber optics can the communication speed be independent of distance. ControlNet has better determinism. Profibus DP (12Mb) suffers from reduced determinism after adding messaging and programming. ControlNet, which uses producer and consumer models, offers better determinism and repeatability (independent of the number of devices on the network). Independent tests showed that for Profibus DP (12Mb): 13 nodes, the standard deviation of determinism for two PLCs was 0.793ms. But if limited messaging (10 bytes) is added, the standard deviation is 2.318ms. After message transmission, the standard deviation is 3 times the original value. The standard deviation of the ControlNet I/O refresh rate is fixed, regardless of how many messages are transmitted. Although Siemens claims that Profibus is flexible and that DP and FMS can operate on the same line, peer-to-peer communication will affect the system’s response time as well as I/O operations with strict timing requirements. Profibus suppliers recommend using different networks (FMS and DP) for peer-to-peer communication and time-critical I/O. ControlNet can handle programming, message transmission, and the transfer of time-critical I/O data over the same cable, without affecting the determinism of the system in any way. Users in Europe consider Profibus to be the network with the worst performance in Europe. (1997 IMS study). ControlNet can detect duplicate addresses through automatic addressing. Using the ControlNet network, users can “plan” I/O refreshes. Rockwell can transfer data and programming between devices at different network layers. Siemens can only provide programming between two levels of the network. Rockwell controllers do not need to manage network traffic: the controllers control and utilize NetLinx services to collect the required data. The ControlNet network has excellent diagnostic and troubleshooting capabilities. Profibus only provides graphical illustration tools and is of no help for diagnosis. In 1999, ControlNet’s growth rate was 50%, and it continued to grow at a high pace in 2002. This post was last edited by 771207 on 2007-12-19 12:52]