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Basics Concepts of PLC
CPU/ RAM/ Hard disk
Key board, Mouse,Remote station (LAN)
CPU/Memory
Inputs
Monitor, Printer, Projector Etc.,
Outputs
Power Supply
OS: Windows XP /SW: MS OfficeSoftware
220V AC, 1 Ph.
PLCComputer
Calculator etc.,Internal
CPU/ RAM/ Flash Card
Push Button, Selector, Limit Switch, PxS, Bus Interface
Solenoids, Relays, Lamps, Motors, HMI
OS: Firmware / SW: Machine Logic
220V AC / 24V DC
Markers, Timers, Counters, FBs
PLC & PC In Comparison
3
Basics Concepts of PLC
Inputs
Outputs
ControllerMachine
Relays, Solenoids, Power contactors
Actuators: Motors, Cylinders, Heaters, Lamps etc.,
Push Buttons, Selector Switches
Limit Switch, Proximity,Reed Switch etc.,
Command Signals Status Signals
HMI
Machine Automation Over View
Basics Concepts of PLC
5
Basics Concepts of PLC
Power Contactor
Over Load Relay
Aux. Contactor
Relays
Relay Boards
Outputs ‐ Switch Gear Products Over View
9
Basics Concepts of PLC
Before the PLC, control, sequencing, and safety interlock logic for manufacturing automobiles was accomplished using hundreds or thousands of relays, cam timers, and drum
sequencers and dedicated closed‐loop controllers. The process for updating such facilities for the yearly model change‐over
was very time consuming and expensive, as electricians needed to individually rewire each and every relay.
History of PLC
10
Basics Concepts of PLC
The PLC is an industrial computer.
It is capable of storing instructions to implement control functions such as
sequencing, timing, counting, arithmetic, data manipulation and communication.
The I/O interfaces provide the connection between the PLC and the
information providers (inputs like pushbuttons, sensors,…) and the controllable
devices (outputs like valves, relays, lamps,…).
What is a PLC ?
11
Basics Concepts of PLC
The PLC controls industrial machines and processes. In different areas of the
industry PLC are being applied, e.g.: materials handling, packaging, palletizing,
milling, boring, grinding, filling,
sorting, weighing,...etc.
Where is the PLC used ?
12
Basics Concepts of PLC
In the past the movements of industrial machines were controlled by relay
circuits. These relay-controlled systems were replaced by PLC.
The primary function of the PLC was to perform the sequential operations that
were previously implemented with relays.
Before we can talk about the working method of an PLC, we must
understand the function of relay circuits.
How does PLC work ?
13
Basics Concepts of PLC
A relay is an electrical switch.
It contains:
a iron core
a coil a switch
and a iron bar connected to the switch
What is a Relay ?
15
Basics Concepts of PLC
… a magnetic field is produced in the coil and the iron core in the coil
becomes magnetic.
I
How does a Relay work ?
16
Basics Concepts of PLC
The electromagnetic force pulls in the switch and...
I
How does a Relay work ?
18
Basics Concepts of PLC
The answer to this question shall be shown with the following example
circuits, A, B, C, and D.
L1
S1
24V
0V
K1K1
technical symbol of a relay
coil
electro magn. connection
internal switch
A).
How does the PLC replace Relay in an electric circuit ?
19
Basics Concepts of PLC
The answer of this question shall be shown with a little example circuit.
K1 L1
S1
24V
0V
Function of the electrical circuit:
When the user presses button S1, the relay
K1 pulls in its internal switch and the lamp
L1 turns on.
B).
How does the PLC replace Relay in an electric circuit ?
20
Basics Concepts of PLC
The answer of this question shall be shown with a little example circuit.
K1 L1
S1
24V
0V
24V
S1
0V
L1
PLCInput
Output
Power
Power
C).
How does the PLC replace Relay in an electric circuit ?
21
Basics Concepts of PLC
The answer of this question shall be shown with a little example circuit.
K1 L1
S1
24V
0V
S1
24V
0V
L1
PLC logic
D).
How does the PLC replace Relay in an electric circuit ?
22
Basics Concepts of PLC
S1
24V
0V
L1
SPS logic
The PLC logic is not a mechanical part of the controller.
The PLC logic is a software program, which runs on the
processor in the PLC. This program has to be created with a
special programming tool on a PC. After downloading the
the program into the PLC, the control
automatically starts the program.
What is PLC logic ?
23
Basics Concepts of PLC
START PB STOP PB PC
PC
TMR1
TMR1
Ph. N220V AC SUPPLY
LADDER PROGRAMI1 I2
Q1
Q1
M1TMR1
En
M1
Trig
Time
Q
T#5s
Q1
RELAY LOGIC
24
Basics Concepts of PLC
Communication module
Power supply Input modules
Output modules
RAM E-EPROMnetwork
power cord
Machine
Programming tool CPU
PLCHow a PLC works: internal
25
Basics Concepts of PLC
Communication module
Power supply Input modules
Output modules
RAM E-EPROMnetwork
power cord
Machine
Programming tool CPU
Central processing unit
PLCHow a PLC works: internal
26
Basics Concepts of PLC
Communication module
Power supply Input modules
Output modules
RAM E-EPROMnetwork
power cord
Machine
Programming tool CPU
Working- and program memory
PLCHow a PLC works: internal
27
Basics Concepts of PLC
Communication module
Power supply Input modules
Output modules
RAM E-EPROMnetwork
power cord
Machine
Programming tool CPU
Program editor and monitoring
PLCHow a PLC works: internal
28
Basics Concepts of PLC
Communication module
Power supply Input modules
Output modules
RAM E-EPROMnetwork
power cord
Machine
Programming tool CPU
Sensor signal input
PLCHow a PLC works: internal
29
Basics Concepts of PLC
Communication module
Power supply Input modules
Output modules
RAM E-EPROMnetwork
power cord
Machine
Programming tool CPU
Actuator command output
PLCHow a PLC works: internal
30
Basics Concepts of PLC
Communication module
Power supply Input modules
Output modules
RAM E-EPROMnetwork
power cord
Machine
Programming tool CPU
Control communication
PLCHow a PLC works: internal
31
Basics Concepts of PLC
Read input signals, store in table
Determine new output state of output module
Write output commands in table
Set output values on output module
Read user program & Copy to RAM
Start PLC from E-EPROMpr
oces
sing
cyc
le
How PLC works: processing cycle
32
Basics Concepts of PLC
Schematic:
Starting position: vac. off, slide right, up; swivel not used (front position)
Sequence of movements:1) slide left 5) move down
2) move down & switch on vacuum 6) switch off vacuum
3) move up 7) move up
4) slide right
pick
place
shuttlecylinder
swiveldevice
up/down cylindersuction
pad
Pick & Place Unit