Historical background of PLC

Industrial automation in process control and manufacturing plants leads to introduce the era of manufacturing plants leads to introduce the era of programmable logic controller in short we call it PLC. In the early 1960s and 1970s relays, timers, counters, and sequencers were all consisting of electro-mechanical in nature. Many control panel contained hundreds of these electro-mechanical devices and, in some cases, a mile or more of wire.The primary negative aspect of electro-mechanical control was that reliability was low, in contrast to the maintenance costs associated with keeping the maintenance costs associated with keeping these panels operating, which were extremely high.The automation in industry complained that there all cost to purchase and replace a single relay could run as high as fifty dollar or more.

A second major factor was the time, expense, and labor required when a change in control needs dictated a control panel modification.dictated a control panel modification. In fact, during the model year changeovers, the auto industry discarded entire control panels and replaced them with new ones as the quickest and cheapest solution.The programmable controller is a solid-state electronic device designed in the early 1970s to replace electro-mechanical relays, mechanical replace electro-mechanical relays, mechanical timers, counters, and sequencers. Keep in mind that the first PLCs were little more than relay re-placers