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Programming Logic Controllers

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Presentation on theme: "Programming Logic Controllers"— Presentation transcript:

1 Programming Logic Controllers
Input/Output Devices & Motor Controls - Chapter 4

2 PLC Control Output control Turn on/off a circuit
Increase/decrease motor speed or torque Input parameters Temperature Pressure Humidity Time

3 Pushbuttons and Switches
Discrete input devices either on or off Connected to PLC inputs When ON they place a positive voltage When OFF they apply zero voltage to the port (NO) Normally open – on until switched off (NC) Normally closed – off until switched on

4 Pushbuttons Momentary Must hold open/closed
Return to normal position when released Locked-position Latch until state changed again physically

5 Switches Manual Require human intervention Automatic
Mechanical or electrical Thermostat Limit switch

6 Switches cont’d Temperature Switch Pressure Switch Liquid level Switch
Flow Switch Float Switch Foot Switch Proximity Switch Led + phototransistor

7 Sensors Digital – high low voltage Analog – varying voltage levels
Proximity Sensors Inductive Sensor – detects current induced from magnetic fields to detect metal Capacitive Sensor – measures change in sensors dielectric caused by nearby objects Optical sensors Emitter + detector Visible, ultraviolet, infrared, or laser Reflection varies with object type

8 Hall Effect Sensor Reed switch
Switched by magnetic fields pull or push Solid state Resist vibration Relay used wire coil to generate magnetic field Reed switch used permanent magnate

9 Ultrasonic Sensor Above 16kHz sound ping (like submarine)
Time for reflected sound to return proportional to object’s distance Accurate over short distances and cheap Electrostatic up to 50kHz Capacitive Longer range but sensitive to environment Piezoelectric up to 1MHz Rugged Crystal lattice produces voltage

10 RADAR Sensors Radio Detection and Ranging Detect metal objects
Not used in factories

11 Cameras & Object Recognition Software
Can identify defects Detecting which parts Quality assurance Getting better

12 Indicators Pilot lights Ammeters & Voltmeters
Red yellow green for states/conditions Ammeters & Voltmeters Looking for undervoltage or overcurrent conditions

13 Relays & Contactors Relay Contactor Solid state relays
like a reed switch but with a coil energized (magnetized) de-energized (demagnetized) Power relay (contactor) or control relay (relay) Contactor Power relay Uses a small amount of voltage to control a large amount Solid state relays No moving parts to wear out perform well in harsh environments

14 Solenoids Convert electrical energy into mechanical motion
Movable plunger at core with spring When energized plunger is pulled When de-energized spring reverses action

15 Motor Control Motor Starters Constant speed motors (on/off)
Contactors and Overload protection overload relays Temperature or thermal overload relay - common Magnetic overload relay - faster but $$$ Motor Drives Soft start stand still to operating speed Plugging when motor reverses direction

16 Electrical Symbols

17 Electrical Symbols



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