Programmable Logic Controllers (PLC) are microprocessor based control systems capable of processing multiple inputs and outputs in order to control machines and industrial functions. With a programmable memory designed to be used easily by engineers with little knowledge of computer language, PLCs operate using a logic language (if A or B is true THEN output C etc). A user will programme the PLC for a given function, the PLC will then monitor the inputs (sensors, switches) and outputs (actuators) according to the program.
PLC block diagram (Bolton, 2009).
First developed in the 1960s, modern PLCs are available in small single units, to larger modular units capable of supporting many numbers of inputs and outputs. Many systems have the ability to be expanded by linking additional units together.
PLCs are designed to be installed in industrial environments and as such, they are usually rugged, well packaged devices so that they are able to withstand vibration, temperature, humidity and noise.
References
Bolton, W. (2009). Programmable logic controllers. Oxford: Newnes.
Crispin, A. (1997). Programmable logic controllers and their engineering applications. London: McGraw-Hill.
Mall.industry.siemens.com, (2016). LOGO! logic module – Industry Mall – Siemens WW. [online] Available at: https://mall.industry.siemens.com/mall/en/ww/catalog/products/5000562?activeTab=order®ionUrl=/ [Accessed 12 Feb. 2016].
Mitsubishielectric.in, (2013). Advanced Modular PLC by Mitsubishi Electric India. [online] Available at: http://www.mitsubishielectric.in/fa/fa-advanced-modular-plc.php [Accessed 12 Feb. 2016].
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