Introduction to Industrial Automation

 2 

Hardware Components for Automation and Process Control....................................19

2.1 Actuators ..............................................................................................................19

2.1.1  Electric Motors ................................................................................................20

2.1.2  Pneumatic Actuators ................................................................................. 24

2.1.3  Micro-Electro-Mechanical Systems ........................................................... 24

2.1.4 Relays .........................................................................................................25

2.1.4.1  Relays’ Operation Principle ........................................................25

2.1.5  Power Relays...................................................................................................... 27

2.1.6  General Purpose Relays ............................................................................. 29

2.1.7  Latching Relays ......................................................................................... 30

2.1.8  Pulse Bistable Relays ....................................................................................31

2.1.9  Solid State Relays ........................................................................................ 32

2.1.10  Electric Contact Classification.....................................................................33

2.1.11  Solenoid Linear Actuators ............................................................................35

2.2 Sensors................................................................................................................... 37

2.2.1  Thermal Overload Relay ........................................................................... 38

2.2.2  Proximity Switches .................................................................................... 40

2.2.3  Photoelectric Switches ................................................................................47

2.2.4  Limit Switches ................................................................................................... 50

2.2.5  Level Switches ............................................................................................52

2.2.6  Flow Switches .................................................................................................... 57

2.2.7  Temperature and Pressure Switches ............................................................59

2.3  Timers, Drum Switches, and Special Components ................................................ 64

2.3.1 Timers ......................................................................................................... 64

2.3.2  Cam Timers ...............................................................................................67

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 Contents

2.3.3  Three-Phase Monitoring Relays................................................................. 69

2.3.4  Reed Relays ............................................................................................... 70

2.3.5  Specific Solenoid Actuators ......................................................................... 71

2.3.6  Counters and Hour Meters ......................................................................... 72

2.3.7 Encoders .............................................................................................73

Review Questions ............................................................................................................. 75