PLC Programming – An Introduction
>PLC programming, the PLC standing for Programmable Logic Controller, is a computer, usually small in size, which has a built-in operating system. The operating system (OS) is specialised and handles any incoming events in real time.
Using computers to automate tasks is taken to an entirely different level with PLC programming. The PLC pulls information from the outside world using inputs like analogue and digital sensors, relays and the like, and interacts with the real world using outputs such as motors, conveyor belts and so on.
The PLC stands in the middle of all of these inputs and outputs, acting as the brains of the whole operation. In milliseconds, the PLC will make its decisions based on the inputs and immediately interact with the outside world using the previously mentioned outputs. Effectively, they’re robots. Automatic machines can be run for years and years with minimal human involvement with a PLC.
The purpose of a PLC is to control machinery, most often in industrial environments. Once a program has been written for the PLC, turning on and off outputs dependant on the input conditions and internal program, it doesn’t need programming again. A PLC by design is made to be programmed the once and to carry on running as required. A good programmer could use a PLC to control their entire house, from opening garage doors to managing a security system or automating the light on/off feature based on input times.
Ladder Logic in PLC Programming
Using Ladder logic you can develop powerful software for programmable logic controllers. Symbols rather than words are used with ladder logic to mimic relay logic control in the real world. Lines interconnect the symbols and are used to indicate current flow through relay. As years go by the number of symbols has risen to afford an improved level of functionality. While looking like a ladder, the program in fact represents the electrical circuit.
In the past if you wanted to control manufacturing equipment you would do so manually, to control devices you’d have to press your fair share of buttons. Machines would have a whole wall of buttons to carry out different commands, most of which could only be used individually, which was still limiting. This automation was a replacement for human hands, but it wasn’t long before the manual control systems in question became a hindrance with the onset of new machine controlled operation technologies, PLCs in particular.
As with computers, PLCs have rapidly evolved over the last few decades. PLCs, while relatively beneficial compared to previous technologies, were rather simple originally when compared with the ones we see today. With PLC programming today the sky is the limit, servo control, data manipulation and proportioning maths functions are a couple of examples of what is possible. You only have to look at some of the processors from Allen-Bradley which boast modules for scripting, enabling you to write write your routines C, VB, and more.
With these improvements in intelligence we’ve recently seen PLCs integrated into electrical communications. Organised hierarchically, PLCs in industrial environments are being plugged into networks which are supervised by a control center, such as SCADA.
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