Saturday, May 14, 2011

Ethernet Management over the PLC CPU





Ethernet The Transmission Control Protocol/Internet Protocol (TCP/IP) is a broadly share out protocol at produc¬tion level and office/IT level and is in no way an out-of-date solution, even if it was built up in the 70s. The Transmission Control Protocol/Internet Protocol (TCP/IP) is a network protocols family, which is also recognized as Internet Protocol because of its major significance for the Internet. Evidence that the protocol is no “game” is provided by the resolution taken by the US Ministry of Defense in 1982 to initiate TCP/IP as a regular for every computer network of military. This standard also presently permits electronic measuring equipment to be incorporated in networks without problems.

No special buses for communication are required to link the PLC to the modules. Other modules can be inserted to the network very simply. A small software development is enough for the PLC to be able to contact the additi¬onal modules. The PLC simply requires a cont¬roller of Ethernet which can control the TCP/IP pro¬tocol. There are both software solutions and hardware solutions for this, where in a hardware solution was utilized because of the many number of measuring results.

A split hardware controller allows high speed communication and decreases the load on the PLC CPU a smaller amount than management of software Ethernet over the PLC CPU. The PLC triggers the modules in the individual measurements, in the synchronous communications process e.g. the acquisition starts as soon as it is needed. The trigger begins in this method, e.g. two measuring over 16 channels each; then the measurement automa¬tically ends.

The values of measuring are not existing “immediately”, but only when the acquirement by the module has been performed. This needs the measuring to be activated by the PLC and the I/O module to then transmit the values to the PLC (Programmable Logic Controller). Asynchronous acquisitions are created re¬gardless of the cycle, e.g. the measuring values are available persistently.


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