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    Module 4 Programmable Logic Control Systems Version 2 EE IIT, Kharagpur 1

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    Lesson 18 Introduction to Sequence/Logic Control and Programmable Logic Controllers Version 2 EE IIT, Kharagpur 2

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    Instructional Objectives After learning the lesson students should be able to A. Define Sequence and Logic Control B. State three major differences between Logic Control and Analog Control C. Define a Programmable Logic Controller and name its major structural components D. Name the major funct...

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    Industrial Example of Discrete Sensors and Actuators There are many industrial sensors which provide discrete outputs which may be interpreted as the presence/absence of an object in close proximity, passing of parts on a conveyor, For example, tables x.y and a.b below show a set of typical sens...

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    Fig. 18.1 Example Industrial Discrete Input and Sensing Devices: Type Output Quantity Energy Source Relay, Contactor voltage electrical Motor Starter motion electrical Lamp indication electrical Solenoid motion electrical On-off Flow Control valve Flow pneumatic...

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    Industrial Example Piston DieUp Sole- noid Upper limit switch Lower limit switch Down Solenoid Fig. 18.2 An Industrial Logic Control Example The die stamping process is shown in figure below. This process consists of a metal stamping die fixed to the end of a piston. T...

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    Issue Logic/Sequence Control Analog Control Logical State-Transition Numerical Different ial/Difference Eqn Simple Model/Easy to buildComplex Model/Hard to buildModel Infrequent Liable to change Signal range/status Signal value Signal Temporal Property (Timed) sequence (Timed)Function/Trajecto...

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    Evolution of the PLC Before the advent of microprocessors, industrial logic and sequence control used to be performed using elaborate control panels containing electromechanical or solid-state relays, contactors and switches, indicator lamps, mechanical or electronic timers and counters etc., al...

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    -ve +ve Power busbars Solenoid Lamp Motorcoil Relay logic A logical function Realized with relays Relays and Contactors Fig. 18.3 The structure of Relay Logic Circuits Rung Logic ] Rung • • •(Virtual) Power Rails Relay LadderFig. 18.4 The structure of Relay Ladder Logic Pro...

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    • Operator control and monitoring • Plant start-up, shut-down Any manufacturing application that involves controlling repetitive, discrete operations is a potential candidate for PLC usage, e.g. machine tools, automatic assembly equipment, molding and extrusion machinery, textile machinery a...

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    Central controller The central controller (CC) contains the modules necessary for the main computing operation of the Programmable controller (PC). The central controller can be equipped with the following: ♦ Memory modules with RAM or EPROM (in the memory sub modules) for the program (mai...

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    Program and Data memory The program and data needed for execution are stored in RAM or EPROM sub modules. These sub modules are plugged into the processors. Additional RAM memory modules can also be connected. Expansion units Modules for the input and output of signals are plugged into expansi...

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    • High speed counting • High accuracy positioning • On-line self-optimizing control • Multi axis synchronisation, interpolation These modules contain additional processors, and are used to relieve the main CPU from the high computational loads involved in the corresponding tasks. Thes...

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    Answers, Remarks and Hints to Points to Ponder Point to Ponder: 1 A. Categorise the following sensor systems as Discrete or Continuous a) thermostat : Discrete b) clinical thermometer : Continuous c) the infrared sensor in TV sets : Discrete B. Categorise the following actuator systems as Discr...

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    controlled by analog speed control of the fan. In a CNC machine the speed of the spindle is controlled by analog means, while auxiliaries, such as coolant flow are controlled by PLCs. Point to Ponder: 4 A. Name three of the most prominent advantages of the PLCs over hardwired Relay Contactor Lo...

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