Saturday, July 16, 2011

The Challenges of PLC-based Control Systems

Let’s look at some of the obstacles engaged with traditional PLC-based systems to know the driving factors to the control of PC-based. This widget machine is proscribed by a PLC throughout electronic modules of input/output (I/O). The PLC, which interprets inputs (sensors) from the machine, carries out logic with those inputs, and locates an output (actuator), which manages the machine widget. The PLC is enclosed by 3 divide computers: an operator panel of microprocessor-based to display production information to the operator; a PC employed to design, download, and check the PLC program; and an added PC used to carry out the functions of supervisory control and data acquisition (SCADA) for example trending, SPC data analysis, and the production data logging. Each of these must be constructed or programmed separately, and linked together to make the entire control system.

Programming the PLC
PLCs are characteristically programmed with relay ladder logic (RLL), which imitates the circuits of electrical relay that were used to manage machines in the 1950’s and 1960’s. A screen of programming viewing a RLL section, The circuit of relay ladder is used to specify power flow though a electrical elements number. The bars on the left and right specify ground and electrical power. Each “rung” of the ladder diagram imitates a circuit that transfers current from power to ground if all of the suitable logic conditions are correct. Each “electrical element” assigns a bit in the memory of PLC that has to be configured with all of the bit, byte, and file locations to add to the challenge. For instance, an input sensor may be constructed as “I:004/13” interpret into input file, word 004, bit 13 (in octal). It would be an underestimation to minimally say that PLC configuration and programming are not perceptive.

Even though helpful in the ‘70s to help engineers and electricians transition from hard-wired electrical relay circuits to the technology of microprocessor, ladder logic has become onerous in the new century. Ladder logic needs specialized training to design and sustain. Every PLC has a unique programming language, a different instructions set, and a different execution set methods. In a lot of cases, different PLCs from the same manufacturer are programmed in a different way and cannot run in the same programs. This would be equal to a personal computer world where a Compaq PC of new generation could not work a program written for an IBM PC or even a previous generation Compaq PC.

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