Monday, September 20, 2010

PLCs with Communications Feature the Most Important





Today’s manufacturing plants must operate faster, more efficiently, and with more flexibility than ever before. To do so, a growing number if manufacturers are implementing open architecture approaches such as PC based DCS and SCADA control systems, there by bringing the speed and flexibility of PC technology to the plant floor. Today traditional PLCs are still in use at most plants, but windows-base PCs are increasingly becoming the preferred control mechanism for new installations.

PLCs have become a favorite tool in the control industry because of their simplicity, robust I/O interface and reliable performance. Traditional PLCs have proven to be information barriers to enterprise-wide data access. Originally the PLCs had no communication capability, but they began to be used in situations where communications was a desirable feature.

At the time being manufacturers of PLCs have devices many communications techniques and pseudo-standard protocols, which are utilized in industry. One may add that the inherent proprietary design of PLCs has limited data access for a number of reasons, such as the limited amount of memory, the nature of programming language (Relay Ladder Logic), and the data access, where data inside the PLC is stored in a data table and accessed by data table location. An important feature of PLCs is that a standard PLC executes only a single program at the time, while an industrial computer is capable of executing several programs or tasks simultaneously in any order.



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