PLC
PLC
PLC
TOPICS TO BE COVERED
• Programmable Logic Controllers
• Relay Device components
• Programmable controller architecture
• programming a programmable controller
• Tools for PLC logic design.
PLC DEFINITION
• A programmable Logic Controller (PLC) is a
specialized computer used for the control and
operation of manufacturing process and
machinery.
• It uses a programmable memory to store
instructions and execute functions including
on/off control, timing, counting, sequencing,
arithmetic, and data handling.
• The PLC is a microcontroller based device
with input/output circuitry that monitors the
status of field connected sensor (inputs) and
controls the attached (output) actuators (motor
–starters , Solenoids , Speed drives, Valves
etc.) according to a user created logic program
stored in the memory.
• PLCs are armoured for severe condition (dust ,
moisture, heat, cold, etc.) and have the facility
for extensive input/output (I/O) arrangements.
These connect the PLC to sensors and
actuators.
• PLCs read limit switches, analogue process
variables (such as temperature and pressure),
and the positions of complex positioning
systems.
• PLCs operate electric motors, pneumatic or
hydraulic cylinders, magnetic relays or
solenoids, or analog outputs.
• The input/output arrangements may be built
into a simple PLC, or the PLC may have
external I/O modules attached to a computer
network that plugs into the PLC.
RELAY DEVICE COMPONENTS
• Switches
• Relays
• Counters
• Timers
Switches
P1
P2
Multiple Throw Multiple Pole
Break-before-make Make-before-break
TERMS
Throw - number of states
Pole - number of connecting moving parts (number of individual circuits).
SPDT
DPST
TYPES OF SWITCHES
1. Basic switch, operated by a mechanical level,
2. Push-button switch,
3. Slide switch,
5. Limit switch,
6. Proximity switch, and
7. Photoelectric switch.
Relays
• The relay is an electromechanical switch used as a
protecting device and also as a controlling device
for various circuits, equipments, and electrical
networks in a power system.
• The electromechanical relay can be defined as an
electrically operated switch that completes or
interrupts a circuit by physical movement of
electrical contacts into contact with each other.
Counters
• Counters are used to detect pieces numbers
and events. Controllers frequently need to
operate with counters in practice.
• For example: a counter in circuit is required if
exactly 20 identical components are to be
conveyed to a converyor belt via a sorting
device.
Timers