Solid-State Devices Used in Industrial Logic Circuits: SOLID-STATE DEVICES USED FOR LOGIC: Programmable Logic Controllers

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When logic circuits become very large, such as in the control of large industrial machinery, it becomes necessary to change the interaction between logic gates from time to time to change the function of the machine control. In the late 1960s and early 1970s, several companies each designed a programmable logic controller (PLC), which is now known as the programmable controller. These early companies included Modicon, Allen-Bradley, and Texas Instruments, and the controllers they designed were made specifically for General Motors. The programmable controllers represented the logic functions with contacts and coils symbols, much like the original relay logic. These symbols are used instead of logic symbols because the electricians and technicians that use the programmable controllers are used to using relay logic. In fact most of the early PLCs were used as relay replacements because they were very cost-effective in providing complex machine control through logic circuits. The PLC provides several other major advantages over logic chips in that they could be reprogrammed easily, they could be troubleshooted with a video screen that showed which contacts are open or closed, and their logic circuit (program) could be stored and downloaded into the machine control at a later date. AMAZON multi-meters discounts AMAZON oscilloscope discounts
Today PLCs are available as the simple, low-cost replacement for relay logic, or to provide complex functions such as data storage, file manipulation, and process control. Each of these topics will be covered in detail in later sections of this guide.
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Thursday, March 17, 2016 10:20