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