Figure 12.1 PLCs
A Programmable Logic Controller is a digital computer used for automation of electromechanichal processess, such as control of machinery on factory assembly lines, control of amusement rides. It uses programmable memory to store instructions and the specific functions that include ON/OFF control, timing counting, sequencing, arithmatic, and data handling. Programmable logic employs electronic processing units in order to process data. The operation of equipment constructed according to this technique is not defined by a circuit diagram, as for that used in hard wired logic, but by a program loaded into the memory of the processing unit. Programmable logic controllers are the basic components used in electronic automated systems and first appeared in the United states in 1969. Today, numerous models of programmable controller are available, from small PLCs suited to dimple applications and installations with a few inputs/outputs, up to multifunction PLCs capable of controlling several thousands of inputs/outputs and designed to control complex processes. The main difference from other computer is that PLCs are armored for severe conditions (dust, moisture, heat, cold, etc) and have the facility for extensive input/output (I/O) arrangements. Another advantages of PLC are : Cost effective for controlling complex systems. Flexible and can be reapplied to control other systems quickly and easy, and allow more sophisticated control because of the computational abilities. The disadvantages of PLC are : Too much work required in connecting wires and difficulty with changes or replacements.
Figure 12.2 Applications of PLC
Source :
http://me.emu.edu.tr/majid/IENG447/IE%20447/PLC%20ppt.pdf
