6.1 Introduction to PLCs ................................................................................................... 193
6.2 Modular Construction of a PLC .......................................................................... 200
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Contents
6.3 PLC I/O Components ......................................................................................... 202
6.4 Digital Input Modules ......................................................................................... 204
6.5 Digital Output Modules ...................................................................................... 209
6.5.1 Technical Specifications for Digital Input/Output Modules ....................212
6.6 Analog Input/Output Modules .............................................................................216
6.6.1 Analog Input Modules .............................................................................216
6.6.2 Accuracy in the Conversion of Analog Signals .........................................219
6.6.3 Analog Output Modules ......................................................................... 220
6.7 Special Purpose Input/Output Modules................................................................ 222
6.7.1 Fast Input Response Modules ................................................................... 223
6.7.2 Stepper Motor Control Modules ............................................................. 223
6.7.3 Three Terms (PID) Control Modules ...................................................... 224
6.7.4 Communication Modules......................................................................... 225
6.8 Central Processing Unit ....................................................................................... 225
6.8.1 Memory Organization ............................................................................ 227
6.8.2 Memory Types .........................................................................................231
6.8.2.1 Read Only Memory (ROM) .....................................................231
6.8.2.2 Random Access Memory (RAM) ..............................................231
6.8.2.3 Erasable Programmable Read Only Memory (EPROM) ...........231
6.8.2.4 Electrically Erasable Programmable Read Only Memory
(EEPROM) .............................................................................. 232
6.8.3 Addressing I/Os and Other Internal Elements ...........................................232
6.9 PLC Expansion and I/O Configuration ................................................................233
6.9.1 Local and Peripheral I/O System ............................................................. 234
6.9.2 I/O System Design .................................................................................. 236
6.10 On the Installation of PLCs ................................................................................ 243
6.10.1 Electrical Enclosure for the PLC Installation ..............................................243
6.10.2 Electromagnetic Interference....................................................................245
6.10.3 Grounding ...............................................................................................249
6.10.4 Electromagnetic Shielding of Cables ........................................................251
6.10.5 Lightning Protection ................................................................................252
6.10.6 Input Devices with Leakage Current—Impedance Adjustment of I/Os ....253
6.10.7 Input Impedance Adjustment ..................................................................256
6.10.8 Output Impedance Adjustment ...............................................................257
6.10.9 Parallelizing Digital Outputs of PLCs—Transitional Protection of I/Os ...259
6.10.10 Starting the Operation of a PLC and Fault Detection ..............................261
Review Questions and Problems..................................................................................... 264
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