3.1.1 Switches 37
3.1.2 Transistor Transistor Logic (TTL) 38
3.1.3 Sinking/Sourcing 39
3.1.4 Solid State Relays 45
3.2.1 Contact Switches 45
3.2.2 Reed Switches 45
3.2.3 Optical (Photoelectric) Sensors 46
3.2.4 Capacitive Sensors 51
3.2.5 Inductive Sensors 55
3.2.6 Ultrasonic 56
3.2.7 Hall Effect 57
3.2.8 Fluid Flow 57