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

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    Lesson 22 The PLC Hardware Environment Version 2 EE IIT, Kharagpur 2

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    Instructional Objectives After learning the lesson students should be able to A. Describe the physical organization of hardware in the PLC B. State typical components and functionality of the main types of modules C. Describe typical Function modules used in PLC systems Introduction In Lesso...

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    Figure 22.1 shows the typical subsystems found on a PLC system. CPU End User Remote I/O Modules Digital I/O Modules Back Plane Power Supply Printer Programmer UnitMemory Analog I/OModules FunctionModules Communication Processor Fig. 22.1 Typical Subsystems for a PLC system MMI ...

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    Memory Modules Central Processor Co ProcessorIO Processor Data BusCommuni- cation Processor Intelligent IO Module Output Module Input Module Fig. 22.2 Functional hardware organization of a PLC System Central Decentral max. 2 m Expansion Unit Expansion Unit Cent...

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    C. Compact - A compact, all-in-one unit (about the size of a shoebox) that has limited expansion capabilities. Lower cost, and compactness make these ideal for small applications. Usually wall mounts. D. Micro - These units can be as small as a deck of cards suitable for wall mounted or table to...

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    In-rack analog I/O 24 256 Application specific function modules 8 64 Process control loops - 60 Process control channels - 20 Network connection: TCP/IP, Modbus +, Ethernet 1 4 Fieldbus connection 0 2 Internal memory (16-bit words) 32K 176K Memory extension (16-bit words) 64K 512K Table 22.1 ...

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    also house channels that output analog/digital signals, as well as excitation circuitry for sensors such as RTDs. An analog module typically contains: Analog to digital (A/D) converters Analog multiplexers and simultaneous sample-hold (S/H) Analog Signal termination PLC bus ports Synchroni...

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    Module Parameter Typical Values Number of input 16/32 Galvanic isolation yes Nominal input voltage + 24 V DC Input voltage range - “0” signal - “1” signal -33…+7V +13…+33V Input current Typically in mA Delay Typically in μs Maximum cable length Typically within 1000m Table 22.3 Ty...

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    10ms switching is typical), they are bulkier, they cost more, and they wear out after a large number of cycles. Relays can switch high DC and AC voltage levels while maintaining isolation. Transistors are limited to DC outputs, and triacs are limited to AC outputs. Transistor and triac outputs ar...

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    Module Parameter Typical Value 1.Number of outputs 16/32 2.Galvanic isolation yes Rated value of Supply voltage Permissible range + 24 V DC 20-30 V Max. output current for “1” signal 0.5 A Short-circuit protection Yes Max. switching frequency for resistive loads, lamps, inductive loads, resp...

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    Count Module A count module senses fast pulses, from sources such as shaft angle encoders, through several input ports. Counting frequency can be as high as 2 MHz and a typically, a counter of length 16 bit or more can count up and down. Counter modules can often also be applied for time and fre...

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    Loop Controller Module A loop controller module is suitable for solving fast control loop problems. A typical module can process several control loops with sampling times varying between a few milliseconds to several seconds. The process output values are measured via analog input ports and are...

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    Answers, Remarks and Hints to Points to Ponder Point to Ponder: 1 A. What is remote i/o? How is it different from the other kinds of i/o? Ans: Local i/o, as contrasted with remote i/o is where the field terminals of the PLC i/o modules are connected directly to the field devices. Each channel ...

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    Ans: So that the user need not face the trouble of signal conditioning for most of the common sensing devices, such as those providing voltage or current outputs, resistance sensors, thermocouples. These can be easily interfaced with the input modules directly. B. How to select between integrat...

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    Ans: First advantage is that the main processor computational burden is reduced significantly. For example, for a control function, that main processor only has to supply the set point and not compute the control input every sampling time. The second advantage is that the application program deve...

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