Programmable logic controllers are small computers used to run electromechanical machinery. Before their invention, strings of relays were used to cause the machinery to perform work in the correct order and manner. But when the product being manufactured changed, the relays had to be rewired by an electrician. PLCs were first used by the automotive industry in the 1960s.
The Features of a PLC
PLCs are designed to withstand heat, vibration, cold and wet -- basically to survive the extreme conditions found in factories. Data and programs are stored on non-volatile storage that does not require power to preserve data. They are programmed with ladder logic, which is a set of sequential instructions that are based on data from the PLC's multiple inputs and outputs. Programming is done by connecting the PLC to an external PC. Once the PLC is programmed, the external PC can be disconnected and the PLC will function on its own.
What Industries Use PLCs?
PLCs can be used in any industry that requires electromechanical machinery to perform repetitive and/or sequential tasks. This includes most forms of manufacturing such as vehicles, appliances and electronics. They are used in the pulp and paper industry, mining, the military, power and water utilities -- anywhere a logical sequence of processes must be followed by machines.
PLCs in Mining
The website PRLog discusses the use of PLCs in the Australian mining industry. PLCs manage the equipment that drill into the rock. This removes human error; the holes are drilled at the angle and to the depth desired with great precision. Underground mining is a dangerous businesses and controlling the machinery remotely means that employees are kept away from the dangerous area where the rock is being cut.
PLCs in Water Management
The Southern California Moulton Niguel Water District uses PLCs to control water levels in their reservoirs. Previously, pumps ran 24 hours a day, keeping the water levels high. Now PLCs start the pumps up in off hours when water is not draining out. This has done two things. It allows the water levels to rise and fall, which has improved water quality and reduced pumping costs by only running the pumps part time.
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