Control Systems

PLC Structure

PLC Structure: The PLC Structure mainly consists of a CPU, memory areas, and appropriate circuits to receive input/output data as shown in Fig. 21.22. A PLC can be considered as a box full of hundreds of thousands of separate relays, counters, timers and data storage locations. (These counters, timers, etc. really do not exists physically but …

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PLC Definition

PLC Definition(Programmable Logic Controller or Program­mable Controller): PLC Definition – Programmable Logic Controller (PLC) or commonly simply called a Program­mable Controller, is a solid state, digital, industrial computer. It is a device that was invented to replace the necessary sequential relay circuits for machine control. The PLC basically operates by looking at its inputs and …

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Cascade Control

Cascade Control with Digital Controllers: A simplified system to control the temperature of a process employing a gas burner using two Cascade Control digital controllers is shown in Fig. 21.21. Each controller has a number of digital inputs and outputs, and also a number of  and outputs, the actual inputs and outputs are limited to …

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Digital Process Control

Digital Process Control: A digital process control functionally needs to operate in much the same way as a conventional analog controller. That is, it must provide facilities to raise or lower the set point and to provide proportional, 2-term or 3-term control. It must be capable of operating in one of many modes including, manual, …

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Direct Digital Control

Direct Digital Control: Developments in digital electronics have led to many industrial processes being computer controlled. The first system used was Direct Digital Control (DDC), in which a computer measured each variable in the process, these signals being used to maintain the required set points in the process. As digital electronics developed, minicomputers become more …

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Temperature Controls

Temperature Controls using an Analog Electronic Controller: A Temperature Controls scheme using an Analog Electronic Controller of Fig. 21.14 is as shown in Fig. 21.16. The temperature setting, derived from a slide wire, is compared with the signal from a thermocouple situated in the oven being heated. The difference between these two voltages is amplified in an …

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