![]() In the late 1960’s an American company named Bedford Associates released a computing device they called the MODICON. The History of Programmable Logic Controllers Instead, digital computers fill the need, which may be programmed to do a variety of logical functions. Systems and processes requiring “on/off” control abound in modern commerce and industry, but such control systems are rarely built from either electromechanical relays or discrete logic gates. ![]() Relays are far from obsolete in modern design, but have been replaced in many of their former roles as logic-level control devices, relegated most often to those applications demanding high current and/or high voltage switching. ![]() Before the advent of solid-state logic circuits, logical control systems were designed and built exclusively around electromechanical relays.
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