The Programmable Logic Controller is a robust industrial computer which accepts input data, both digital and analogue, from switches and sensors and controls outputs to drive devices such as motors, pneumatic devices and status indicators. At its most basic the PLC substitutes relay logic circuits, at its most advanced it can implement Proportional Integral and Derivative (PID) control algorithms over networks. While the Programmable Controller is by far the most common process control mechanism in the manufacturing spectrum of large to small business it has also found a niche in environment control, food processing, mining and in automated test equipment.
Programmable controllers were developed in the U.S. for the motor manufacturing industry in the 1960s. They appeared in the Irish industrial scene By the late 1970s. Today due to their increasing sophistication and falling costs they are to be found in the smallest production environment. The programming environment PLC may be dedicated terminal or a Personal Computer (PC). Latterly, with the event of the range of programming languages defined by IEC 6-1131 the PC is the favoured programming environment. Ladder Logic (LL) is currently the most popular language. There is however, anecdotal evidence that the other defined languages are slowly gaining acceptance.
As the PLC is part of a system automated there are several modules that should be included, or be a prerequisite, in any course. Those modules are design of electrical, software engineering, and in some cases, mechanical design. Software engineering together with applying a SLDC (Software Development Life Cycle) approach to the system being designed and the ability to write the control program. Electrical design encompasses design of electrical panel (and construction) to the relevant standard. The PLC is apart being run as a “stand alone” course is now an integral part of courses ranging from agricultural engineering to mechatronics and industrial automation. PLC courses, such as control engineering courses, must deliver “a balance of practical skills and theoretical knowledge” and as such are laboratory based.
Increasingly, in response to demands from industry PLC courses are being run in-house, in training rooms, away from the traditional venue of the automation laboratory using hardwired “kits” and PC based simulators.