Programming Logic Controllers

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 • Red yellow green for states/conditions • Ammeters & Voltmeters • Looking for undervoltageor overcurrent conditions

13. Relays & Contactors • Relay • 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 http://www.techtransfer.com/resources/wiki/entry/1829/#Contacts

17. Electrical Symbols http://www.wadeinstruments.com/ez_schematics/description.htm

18. http://www.wadeinstruments.com/ez_schematics/description.htm

19. http://www.industrial-electronics.com/image/15-5.jpg